Early zebrafish development itis in

Available online at www.sciencedirect.com

Early zebrafish development: It’s in the maternal genesElliott W Abrams and Mary C Mullins

The earliest stages of embryonic development in all animals

examined rely on maternal gene products that are generated

during oogenesis and supplied to the egg. The period of

maternal control of embryonic development varies among

animals according to the onset of zygotic transcription and the

persistence of maternal gene products. This maternal

regulation has been little studied in vertebrates, owing to the

difficulty in manipulating maternal gene function and lack of

basic molecular information. However, recent maternal-effect

screens in the zebrafish have generated more than 40 unique

mutants that are providing new molecular entry points to the

maternal control of early vertebrate development. Here we

discuss recent studies of 12 zebrafish mutant genes that

illuminate the maternal molecular controls on embryonic

development, including advances in the regulation of animal–

vegetal polarity, egg activation, cleavage development, body

plan formation, tissue morphogenesis, microRNA function and

germ cell development.

Address

University of Pennsylvania School of Medicine, Department of Cell and

Developmental Biology, 1211 BRB II/III, 421 Curie Blvd, Philadelphia,

PA 19104-6058, United States

Corresponding author: Mullins, Mary C ([email protected])

Current Opinion in Genetics & Development 2009, 19:396–403

This review comes from a themed issue on

Pattern formation and developmental mechanisms

Edited by Kathryn Anderson and Kenneth Irvine

Available online 14th July 2009

0959-437X/$ – see front matter

# 2009 Elsevier Ltd. All rights reserved.

DOI 10.1016/j.gde.2009.06.002

IntroductionThe zebrafish has emerged as a premiere genetic tool for

studying vertebrate development. In the 1990s forward

genetic screens identified numerous zygotic mutants

defective in key molecules important in early embryonic

development [1–7]. Recently, a major focus has shifted

towards more specialized screens, including the identi-

fication of maternal-effect mutations in adult screens in

the zebrafish. Since the earliest stages of development

are driven primarily by maternal gene products, the

identification of corresponding mutants is crucial to

provide genetic entry points to known maternally con-

trolled processes, which are still poorly understood in

vertebrates.


Maternal-effect screens have identified over 40 mutants

affecting many early developmental processes (Figure 1).

Collectively, these mutants have defects in oocyte de-

velopment [8], egg activation [8,9], embryonic cleavage

[8–11], patterning and morphogenesis [9–11]. New stu-

dies have focused on the molecular identification of the

corresponding mutant genes, a key step to understand-

ing the molecular mechanisms governing the very

earliest stages of embryogenesis. The results have

unveiled novel and known genes with unanticipated

roles in early development. Mutants generated by

reverse genetic TILLING methods in the zebrafish

have also recently revealed important roles for small

noncoding RNA molecules, miRNAs [12] and piRNAs

[13,14], in the regulation of maternal processes in zebra-

fish development.

In this review, we highlight recent contributions to the

molecular regulation of animal–vegetal polarity in the

oocyte and egg, maternal gene regulation of early embryo-

nic patterning, tissue morphogenesis and small noncoding

RNA molecules, which are emerging as important players

in germ line development.

Molecular insights into zebrafish animal–vegetal polarityIn frogs and fish, the first developmental asymmetry of

the embryo is the animal–vegetal axis, which predicts the

anterior–posterior axis of the embryo. This asymmetry is

established during early stages of oogenesis and is first

marked by formation of the Balbiani body (Bb; also

referred to as the mitochondrial cloud) adjacent to the

germinal vesicle (the oocyte nucleus) in stage I oocytes.

The Bb position predicts the location of the vegetal pole,

but its presence is only transient, as it disassembles by

stage II of oogenesis. The Bb is composed of a collection

of mitochondria, ER, germinal granules and several germ

plasm mRNAs (reviewed in [15]). Recently, a thorough

study recapitulated in zebrafish transgenic constructs the

localization pattern of three Bb-localized transcripts. The

30 UTRs of nanos, vasa and dazl directed their localization

initially to the Bb and then to the vegetal cortex of the

oocyte [16�], probably via the METRO pathway

described in Xenopus [17]. The ensuing distribution at

the vegetal cortex differs among these transcripts: dazlpersists at the vegetal cortex, vasa extends around the

cortex, and nanos becomes unlocalized (Figure 2),

suggesting, unexpectedly, that coordinate localization

of germ plasm components is followed by their redistri-

bution to distinct locations. However, after fertilization of

the egg, these germ plasm RNAs reunite in the blastodisc

at the animal pole, where they localize to the germ plasm

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http://dx.doi.org/10.1016/j.gde.2009.06.002

Maternal Zebrafish Development Abrams and Mullins 397

Figure 1

Maternal-effect mutant genes in zebrafish disrupt development at distinct stages. Mutants discussed here are indicated in red. acytokinesis [11],

atomos [9], aura [9], barrette [9], bo peep [9], bedazzled [10], blistered [10], claustro [9], cobblestone [9], emulsion [8], golden gate [9], indivisible [8],

irreducible [8], jumpstart [8], kwai [9], misson impossible [9], nebel [9], over easy [8], poky [10], pollywog [10], pug [10], slow [10], ruehrei [8], souffle [8],

screeching halt [10], sunny side up [8], under repair [9], waldo [9], weeble [9].

Figure 2

mRNA localization during oocyte development. During stage I of oogenesis buc, nanos, vasa and dazl transcripts localize to the Balibani body (Bb,

pink), while cyclinB begins to be localized to the animal pole. By stage II of oogenesis the Bb has disassembled, leaving buc, vasa and dazl mRNAs at

the vegetal cortex, whereas nanos becomes unlocalized, and pou2 becomes localized to the animal pole. Note vasa has a broad vegetal cortical

domain at stage II. By stage III bruno-like and mago nashi become vegetally localized (late pathway); now buc, and Vg1 are localized to the animal pole

and vasa is localized radially at the cortex. Animal (An) pole is to top and vegetal (Ve) to bottom.

www.sciencedirect.com Current Opinion in Genetics & Development 2009, 19:396–403

398 Pattern formation and developmental mechanisms

at the cleavage furrows of the four-cell stage embryo

[16�,18–21].

Three regions within the dazl 30UTR are crucial for (1)

localization to the Bb, (2) anchoring to the vegetal cortex,

and (3) localization to the cleavage furrows in the early

embryo [16�]. Interestingly, although the 30UTR of the

nanos-related gene Xcat2 in Xenopus, also localizes it to

the Bb and vegetal cortex in zebrafish, little sequence

similarity is evident in the 30UTRs of Xcat2, and zebrafish

nanos, dazl and vasa [16�], suggesting either small motifs,

or secondary/tertiary structure of the UTRs are con-

served. Thus, germ plasm mRNA localization occurs in

a stepwise, spatiotemporal fashion, with conserved fea-

tures to the transport systems in Xenopus [16�].

Recent studies have provided genetic access into the

mechanisms of Bb formation and germ plasm assembly

in the oocyte. The maternal-effect mutant bucky ball (buc),identified through its animal–vegetal polarity egg pheno-

type [8], is defective in Bb formation and early oocyte

polarity, as animal pole markers are expanded radially and

vegetal pole markers are unlocalized [22�,23�]. Buc is

required for early vegetal pole mRNA localization that

occurs via the Bb, as well as late vegetal pole localization

that occurs after Bb dissociation, which is postulated to

depend on the early pathway [24,25]. Thus, the failure of

late vegetal pole mRNA localization in buc mutant

oocytes may be secondary to the lack of Bb formation.

Buc functions to promote vegetal and exclude animal

pole identity also in the surrounding follicle cell layer,

preventing the formation of multiple micropylar cells, an

animal pole-specific follicle cell fate. Thus, patterning of

the oocyte and surrounding somatic follicle cell layer

appears to be coordinated through an as yet unknown

signaling mechanism [22�].

Recently the molecular identity of buc was determined to

be a novel 639 amino acid protein [23�], first identified as

XVelo1 in Xenopus [26]. The predicted Buc protein

contains no known functional motifs. The localization

of buc mRNA is dynamic during oocyte development,

initially localizing to the Bb, moving vegetally and then

ultimately localizing to the animal pole during late

oogenesis [23�] (Figure 2). A Buc-GFP fusion also loca-

lizes to the Bb and, interestingly, to the germ plasm of the

embryo and can induce ectopic germ cells in the embryo

[23�]. Buc homologues in other vertebrates have low

predicted amino acid conservation, indicating that it

has evolved at a relatively accelerated rate. Interestingly,

the human version lacks a complete open reading frame,

suggesting that it has lost its function all together in

humans or functions as an RNA. In zebrafish Buc clearly

functions as a protein, since a nonsense mutation trun-

cating it by just 30 amino acids causes a failure in Bb

formation [23�]. However, the buc RNA could have

additional functions in Bb formation and animal–vegetal


polarity, similar to oskar in Drosophila [27], also a germ

plasm component. Future structure-function exper-

iments of the buc RNA/protein, together with the iso-

lation of interacting partners will unravel mechanistically

how this novel gene functions.

Egg activation molecular geneticsIn zebrafish egg activation is marked by cortical granule

exocytosis (CGE), chorion elevation and the segregation

of cytoplasm from the yolk to the animal pole to form the

single cell blastodisc. Embryos derived from brom bones(brb) mutant females are defective in this process [28].

The egg activation defect is a result of failure of inositol

1,4,5-triphosphate (IP3) signaling, which induces a Ca2+

wave crucial for normal egg activation in all animals

examined. The reinstatement of either IP3 or Ca2+ in

brb mutant eggs can rescue the egg activation defect [28].

brb was shown to encode heterogeneous nuclear ribonu-

cleoprotein I (hnRNP I), probably regulating during

oogenesis the production of an egg activation signaling

component. hnRNP I has been previously shown to be

important in a variety of developmental processes in-

cluding translational control in oogenesis [29], spermato-

genesis [30] and RNA localization [31–34]. Thus, brbmutants reveal yet another developmental function for

hnRNP I, that is, a role in egg activation.

Cleavage stage molecular geneticsMaternal-effect screens have yielded a significant num-

ber of mutations affecting cleavage development [8–11],

although most of the mutant genes have yet to be cloned.

cellular atoll (cea) mutants fail to undergo cleavages at the

second cell division and beyond [8,35], and was recently

shown to encode the centriolar component sas-6 [35].

Interestingly, as sperm normally provide the centriole to

the zygote, cea also has a paternal-effect function,

whereby wild-type eggs fertilized with cea mutant sperm

result in inviable tetraploid embryos. Since the cleavage

stage of development is primarily under maternal control,

the eventual molecular identification of other maternal-

effect mutant genes functioning during this period will

enhance our understanding of this important stage of

development.

The maternal-effect cellular island (cei) mutant displays an

early defect in cleavage furrow formation [8]. cei encodes a

hypomorphic allele of Aurora B Kinase [36], a protein

previously shown to be important in several aspects of cell

division in other systems (reviewed in [37]). Aurora B

Kinase function is vital zygotically later in zebrafish

embryogenesis, as a null retroviral insertional allele

reveals furrow defects during this period [36,38]. Inter-

estingly, the maternal-effect cei allele causes a specific

defect in distal furrow formation during the early cleavage

stage, while medially positioned furrows can form, prob-

ably owing to intact mitotic spindle-derived signals med-

iating medial furrow formation [36]. The ability of the cei



Figure 3

The role of BMP and early and late Wnt signaling in dorsoventral patterning. (a) Maternal Pou2 induces early zygotic bmp ligand expression. bmp

expression is initially present throughout the blastoderm (grey). An early maternal Wnt signal from the yolk cell promotes future dorsal organizer (DO)

formation. (b) By the late blastula stage (50% epiboly), a BMP activity gradient (highest ventrally (black)) is established that promotes ventral fates. At

this stage Wnt 8 signaling opposes dorsal fate specification ventrally. Ventral is positioned to the left and dorsal to the right.

mutant Aurora B Kinase protein to mediate all its cyto-

kinesis functions zygotically, but its inability to mediate

distal furrow formation in the cleavage embryo may be

related to unique requirements for astral microtubules

and Aurora B Kinase to divide the large cells of the very

early embryo [36].

Molecular genetic advances in maternalregulated patterning and morphogenesisIn fish and amphibians, the dorsoventral embryonic axis is

established through a maternally regulated Wnt/bcatenin

pathway. Several zebrafish maternal-effect mutants with

defects in dorsoventral axis formation have been ident-

ified. The maternal-effect ventralized mutants hecate and

tokkaebe produce embryos lacking a dorsal organizer and

consequently are radially ventralized. Although hecate and

tokkaebe have not yet been molecular defined, injection/

rescue experiments with Wnt signaling pathway com-

ponents indicates that they act upstream of, or within a

Wnt/bcatenin signaling pathway, respectively, to induce

the dorsal organizer [39–41]. tokkaebe probably corre-

sponds to a novel component of the Wnt pathway, since

no known Wnt components are found within the 0.5 cM

interval containing the tokkaebe mutation [41].

The maternal-effect ventralized mutant ichabod is caused

by a specific loss of maternal bcatenin2 function [42].

Two bcatenin genes have been identified in the zebrafish

genome; however, only bcatenin2 is essential maternally


to induce the dorsal organizer through a Wnt signaling

pathway. Interestingly, the maternal, dorsal organizer

Wnt/bcatenin2 pathway also functions to repress expres-

sion of a later Wnt8/bcatenin pathway that opposes dorsal

specification ventrally [42] (Figure 3). In zebrafish this

late blastula Wnt pathway depends on both bcatenin1 and

bcatenin2 function and is mediated by zygotic Wnt8

signaling ventrally [42–45]. Thus in the absence of both

bcatenin1 and bcatenin2 function, early dorsal organizer

formation fails; however, at later stages the ventral Wnt8

pathway also fails to oppose dorsal fate specification

ventrally. The result is the formation of dorsal tissues

circumferentially. These results show, surprisingly, that

at a late blastula stage circumferential organizer-like

tissue can form in the absence of a maternal Wnt/bcatenin

pathway and independently of Wnt/bcatenin signaling

entirely.

The transcription factor pou2/oct4 also acts maternally in

dorsoventral patterning and morphogenesis [46,47],

revealing additional roles to its described maternal func-

tion in endoderm specification [48,49]. Loss of both

maternal and zygotic (MZ) Pou2 causes severe dorsaliza-

tion owing to failure to induce bmp ligand gene expres-

sion, which functions in ventrolateral tissue specification

[46]. These results demonstrate that ventral specification

via the BMP signaling pathway is not a default pathway,

as previously thought, but instead is initiated by maternal

Pou2/Oct4 in the early embryo [46] (Figure 3). MZPou2



Figure 4

miRNA regulation of germ line development. In the soma miR-430

inhibits expression of germ line specific genes (GLSGs). In the germ line

Dnd blocks miR-430-mediated repression of GLSGs. Note that an

unidentified factor X is required in the soma to silence GLSGs that are

not regulated by miR-430. Soma shown in grey; germ line in purple.

also regulates the morphogenic process of epiboly, the

thinning and spreading of the blastoderm over the yolk

cell, through functions in yolk cell microtubule formation,

cell adhesive properties and blastoderm cell movements

via a cell non-autonomous mechanism [46,47]. Together,

these studies reveal that the renowned pou2/oct4 stem cell

gene in mammals is a key maternal regulator of early

zebrafish development.

The betty boop (bbp) mutant, identified in a maternal-

effect screen, is a strictly, maternally acting gene reg-

ulating the morphogenic process of epiboly [10,50�].Embryos from bbp mothers develop normally until they

reach 50% epiboly at which point the embryo abruptly

bursts via a presumptive premature constriction of the

actin cytoskeleton in the yolk cell [50�]. Interestingly,

bbp was recently shown to encode the zebrafish homol-

ogue of Mitogen Activated Protein Kinase Activated

Protein Kinase 2 (MAPKAPK2), a target of p38 MAP

kinase (MAPK) in cell culture systems [51]. During

zebrafish epiboly, p38 MAPK also appears to activate

MAPKAPK2, as a dominant-negative p38 MAPK causes

the same epiboly defect as loss of bbp [50�]. Neither p38

MAPK, nor MAPKAPK2 have been previously impli-

cated in tissue morphogenesis. Thus, the identification

and cloning of the bbp gene is a model genetic case for an

unexpected pathway being placed in a developmental

process, in this case epiboly, which may not have

been considered in a candidate-gene reverse genetic

approach.

Small RNA molecules in early developmentSmall noncoding RNAs are emerging as important

players in early zebrafish development. Maternal-zygo-

tic (MZ) mutant embryos of the microRNA (miRNA)-

processing enzyme Dicer exhibit early embryonic

defects in gastrulation, somitogenesis, brain morpho-

genesis and heart development [52]. By removing the

strong maternal component of dicer, MZ-dicer mutant

embryos are completely devoid of miRNA processing

and therefore, devoid of all miRNA function. miRNAs

negatively regulate target genes by binding to their

30UTR, promoting deadenylation, translational repres-

sion and/or ultimately degradation of the transcript

(reviewed in [53]). In zebrafish, the predominantly

expressed miRNA during early embryogenesis is miR-

430, which is first expressed at the mid-blastula tran-

sition (MBT), and is not expressed maternally [54]. A

central finding revealed by the loss of miR-430 through

MZ-dicer is its role in the clearance of maternal mRNAs

at the MBT. In MZ-dicer mutant embryos, maternal

mRNAs abnormally persist beyond the MBT [12]. To

date, no maternal miRNAs have been reported in the

zebrafish embryo [54]. Thus, it is unclear whether the

maternal role of dicer is to primarily process miR-430 at

the MBT or in addition, also process unidentified

maternal miRNA(s).


Inhibition of miRNA function plays a role in germ line

development. nanos1 is expressed early in germ line

development and a mutant, generated through TIL-

LING methods, demonstrates its maternal requirement

for PGC survival and a function in the adult in maintain-

ing oocyte production [55]. nanos1 is resistant to miRNA

repression in the germ line, but not in the soma, promot-

ing its specific expression in the germ line [56]. This

resistance is conferred, at least partly, by the maternally

expressed germ cell-localized RNA binding protein Dead

End (Dnd), which interacts with the nanos1 30UTR,

presumably blocking the binding of miR-430 [57�]. Inter-

estingly, this resistance to miRNA repression is also found

in another germ plasm mRNA, Tudor-domain-contain-

ing-7 (Tdrd-7) [56], suggesting a general mechanism

involving Dnd in influencing germ cell-specific gene

expression (Figure 4).

Germ plasm mRNA resistance to miRNA regulation is

not universal, however, as the dnd 30 UTR itself lacks a

miR-430 site and therefore is presumably not repressed in

the soma by miRNAs [58]. Since dnd maternal transcripts

are dramatically eliminated in the soma about one hour

after the MBT [59], independently of miR-430 regula-

tion, it suggests the existence of additional mode(s) of

modulating maternal transcripts at this crucial develop-



mental transition. Likewise, vasa removal from the soma

is also independent of miR-430 regulation [56]. Thus, an

unknown, possibly common additional mechanism elim-

inates dnd and vasa transcripts from the soma.

A Dicer-independent class of small noncoding RNAs,

known as piRNAs or Piwi associated RNAs, appear to

be germ line specific [13,14,60,61]. Piwi proteins are

important for target gene silencing [62]. Presumptive

null, zygotic mutations in either of two piwi homologues

in zebrafish, ziwi and zili, cause the progressive loss of

germ cells between three and seven weeks of age [13,14].

Mutant adults are phenotypically male, consistent with

recent studies demonstrating that zebrafish develop phe-

notypically as male when eliminating the germ line

[13,63,64]. Interestingly, there is a maternal-effect meio-

tic progression defect in zili hypomorphic mutants.

Although mutant eggs can be fertilized, they fail to

undergo meiosis I and II [13]. Piwi proteins in the mouse

function to repress transposon activity in the germ line

[65,66]. The meiotic defects in zili hypomorphs mutants,

however, are not linked to increased transposon activity as

measured by quantitative RT-PCR and in situ hybridiz-

ation [13]. These findings reveal a novel function for

piRNAs, whose function in vertebrates was previously

thought confined to regulating transposon activity in the

germ line [13].

Future outlookA major hindrance to the molecular cloning of chemically

induced mutant genes in zebrafish is the incomplete

assembly of the genomic sequence. This obstacle is

becoming less of an issue with recent improvements to

the assembly (currently Zv8; www.sanger.ac.uk). As exist-

ing gaps are eliminated and the genome sequence is

completed, the molecular cloning of maternal-effect

mutant genes will be greatly accelerated.

The investigation of the maternal functions of essential

zygotic genes will be more difficult to study. Although

germ line chimeric analysis is a successful method to

examine the maternal function of zygotic lethal genes in

zebrafish [67], it is quite labour intensive and would be

impractical for large throughput analysis of such maternal

function. This problem may be overcome by employing

techniques that utilize mitotic recombination, a principle

heavily relied upon in Drosophila genetics [68]. RecQ

helicases are known to prevent recombination during

replication [69]. Induced mitotic recombination through

the suppression of RecQ helicases was recently demon-

strated in zebrafish [70]. This approach can generate

mutant clones from heterozygous cells at a significant

frequency (�1.7–3.4%) [70]. With further improvements

in this technology, mitotic recombination could poten-

tially be used to generate homozygous mutant germ line

clones of zygotic lethal mutations from heterozygous

individuals. Such germ line mosaic females would gen-


erate maternally deficient eggs and embryos, allowing the

study of the maternal gene function.

Reverse genetic techniques are very valuable comp-

lements to forward genetic approaches in the zebrafish.

Antisense morpholino oligos are widely used to block

translation or disrupt splicing [71,72]. However, the func-

tion of maternal protein already present in the egg cannot

be blocked by morpholino injection into the egg,

although advances in oocyte cell culture methods may

make it possible to use this method in the future to

examine maternal gene functions. Reverse genetic

approaches that rely on induction of genomic sequence

alterations are considerably more laborious, but generate

robust loss-of-function reagents. Recently, the TILLING

(Target Induced Local Lesions in Genomes) approach

[13,14,55], as well as the zinc finger nuclease approach

designed to mutate a specific sequence of the genome

[73–75], have been very successful in generating mutants

in zebrafish. Hence, TILLING and zinc finger nuclease

strategies look very promising for eliminating gene func-

tion of suspected maternal-effect genes in zebrafish in the

future.

AcknowledgementsWe thank Lee Kapp for comments on the manuscript, and Eric Weinbergand Mate Varga for helpful discussion. Funding was provided by NIH grantHD050901 to MCM.

References and recommended readingPapers of particular interest, published within the period of review,have been highlighted as:

� of special interest�� of outstanding interest

1. Driever W, Solnica-Krezel L, Schier AF, Neuhauss SC, Malicki J,Stemple DL, Stainier DY, Zwartkruis F, Abdelilah S, Rangini Z et al.:A genetic screen for mutations affecting embryogenesis inzebrafish. Development 1996, 123:37-46.

2. Hammerschmidt M, Pelegri F, Mullins MC, Kane DA, Brand M, vanEeden FJ, Furutani-Seiki M, Granato M, Haffter P, Heisenberg CPet al.: Mutations affecting morphogenesis during gastrulationand tail formation in the zebrafish, Danio rerio. Development1996, 123:143-151.

3. Kane DA, Hammerschmidt M, Mullins MC, Maischein HM,Brand M, van Eeden FJ, Furutani-Seiki M, Granato M, Haffter P,Heisenberg CP et al.: The zebrafish epiboly mutants.Development 1996, 123:47-55.

4. Kane DA, Maischein HM, Brand M, van Eeden FJ, Furutani-Seiki M, Granato M, Haffter P, Hammerschmidt M, Heisenberg CP,Jiang YJ et al.: The zebrafish early arrest mutants. Development1996, 123:57-66.

5. Mullins MC, Hammerschmidt M, Kane DA, Odenthal J, Brand M,van Eeden FJ, Furutani-Seiki M, Granato M, Haffter P,Heisenberg CP et al.: Genes establishing dorsoventral patternformation in the zebrafish embryo: the ventral specifyinggenes. Development 1996, 123:81-93.

6. Solnica-Krezel L, Stemple DL, Mountcastle-Shah E, Rangini Z,Neuhauss SC, Malicki J, Schier AF, Stainier DY, Zwartkruis F,Abdelilah S et al.: Mutations affecting cell fates and cellularrearrangements during gastrulation in zebrafish. Development1996, 123:67-80.

7. Stemple DL, Solnica-Krezel L, Zwartkruis F, Neuhauss SC,Schier AF, Malicki J, Stainier DY, Abdelilah S, Rangini Z,


http://www.sanger.ac.uk/


Mountcastle-Shah E et al.: Mutations affecting development ofthe notochord in zebrafish. Development 1996, 123:117-128.

8. Dosch R, Wagner DS, Mintzer KA, Runke G, Wiemelt AP,Mullins MC: Maternal control of vertebrate development beforethe midblastula transition: mutants from the zebrafish I. DevCell 2004, 6:771-780.

9. Pelegri F, Dekens MP, Schulte-Merker S, Maischein HM, Weiler C,Nusslein-Volhard C: Identification of recessive maternal-effectmutations in the zebrafish using a gynogenesis-basedmethod. Dev Dyn 2004, 231:324-335.

10. Wagner DS, Dosch R, Mintzer KA, Wiemelt AP, Mullins MC:Maternal control of development at the midblastula transitionand beyond: mutants from the zebrafish II. Dev Cell 2004,6:781-790.

11. Kishimoto Y, Koshida S, Furutani-Seiki M, Kondoh H: Zebrafishmaternal-effect mutations causing cytokinesis defect withoutaffecting mitosis or equatorial vasa deposition. Mech Dev2004, 121:79-89.

12. Giraldez AJ, Mishima Y, Rihel J, Grocock RJ, Van Dongen S,Inoue K, Enright AJ, Schier AF: Zebrafish MiR-430 promotesdeadenylation and clearance of maternal mRNAs. Science2006, 312:75-79.

13. Houwing S, Berezikov E, Ketting RF: Zili is required for germ celldifferentiation and meiosis in zebrafish. EMBO J 2008, 27:2702-2711.

14. Houwing S, Kamminga LM, Berezikov E, Cronembold D, Girard A,van den Elst H, Filippov DV, Blaser H, Raz E, Moens CB et al.: Arole for Piwi and piRNAs in germ cell maintenance andtransposon silencing in Zebrafish. Cell 2007, 129:69-82.

15. Kloc M, Bilinski S, Etkin LD: The Balbiani body and germcell determinants: 150 years later. Curr Top Dev Biol 2004,59:1-36.

16.�

Kosaka K, Kawakami K, Sakamoto H, Inoue K: Spatiotemporallocalization of germ plasm RNAs during zebrafish oogenesis.Mech Dev 2007, 124:279-289.

A very thorough analysis of the 30UTR of dazl involving a series oftransgenic animals demonstrates that distinct regions are required forsuccessive steps in dazl localization during early oogenesis and in germplasm localization in the embryo, implicating a more general utility of theearly Xenopus METRO oogenesis localization pathway in zebrafish.

17. Kloc M, Etkin LD: Two distinct pathways for the localization ofRNAs at the vegetal cortex in Xenopus oocytes. Development1995, 121:287-297.

18. Theusch EV, Brown KJ, Pelegri F: Separate pathways of RNArecruitment lead to the compartmentalization of the zebrafishgerm plasm. Dev Biol 2006, 292:129-141.

19. Knaut H, Pelegri F, Bohmann K, Schwarz H, Nusslein-Volhard C:Zebrafish vasa RNA but not its protein is a component of thegerm plasm and segregates asymmetrically before germlinespecification. J Cell Biol 2000, 149:875-888.

20. Koprunner M, Thisse C, Thisse B, Raz E: A zebrafish nanos-related gene is essential for the development of primordialgerm cells. Genes Dev 2001, 15:2877-2885.

21. Yoon C, Kawakami K, Hopkins N: Zebrafish vasa homologueRNA is localized to the cleavage planes of 2- and 4-cell-stageembryos and is expressed in the primordial germ cells.Development 1997, 124:3157-3165.

22.�

Marlow FL, Mullins MC: Bucky ball functions in Balbiani bodyassembly and animal-vegetal polarity in the oocyte and folliclecell layer in zebrafish. Dev Biol 2008, 321:40-50.

This is a study of the first mutant in vertebrates known to be defective inBalbiani formation, the earliest oocyte asymmetric structure in verte-brates, which is conserved from insects to mammals and first describedover 150 years ago. The analysis implicates this gene in setting up theanimal–vegetal axis of early oocytes and shows that patterning of theoocyte and surrounding follicle cell layer is coordinated, probably througha signaling mechanism.

23.�

Bontems F, Stein A, Marlow F, Lyautey J, Gupta T, Mullins MC,Dosch R: Bucky ball organizes germ plasm assembly inzebrafish. Curr Biol 2009, 19:414-422.


This study identifies the molecular nature of the bucky ball gene as anovel, rapidly evolving gene and demonstrates that its overexpressioncan result in ectopic germ cells, implicating it in germ plasm assembly.

24. Kloc M, Larabell C, Etkin LD: Elaboration of the messengertransport organizer pathway for localization of RNA to thevegetal cortex of Xenopus oocytes. Dev Biol 1996, 180:119-130.

25. King ML, Messitt TJ, Mowry KL: Putting RNAs in the right placeat the right time: RNA localization in the frog oocyte. Biol Cell2005, 97:19-33.

26. Claussen M, Pieler T: Xvelo1 uses a novel 75-nucleotide signalsequence that drives vegetal localization along the latepathway in Xenopus oocytes. Dev Biol 2004, 266:270-284.

27. Jenny A, Hachet O, Zavorszky P, Cyrklaff A, Weston MD,Johnston DS, Erdelyi M, Ephrussi A: A translation-independentrole of oskar RNA in early Drosophila oogenesis. Development2006, 133:2827-2833.

28. Mei W, Lee KW, Marlow F, Miller AL, Mullins MC: hnRNP I/brombones is required to generate the Ca2+ signal that causes eggactivation in the zebrafish. Development, in press.

29. Besse F, Lopez de Quinto S, Marchand V, Trucco A, Ephrussi A:Drosophila PTB promotes formation of high-order RNPparticles and represses oskar translation. Genes Dev 2009,23:195-207.

30. Robida MD, Singh R: Drosophila polypyrimidine-tract bindingprotein (PTB) functions specifically in the male germline.EMBO J 2003, 22:2924-2933.

31. Cote CA, Gautreau D, Denegre JM, Kress TL, Terry NA, Mowry KL:A Xenopus protein related to hnRNP I has a role in cytoplasmicRNA localization. Mol Cell 1999, 4:431-437.

32. Kress TL, Yoon YJ, Mowry KL: Nuclear RNP complex assemblyinitiates cytoplasmic RNA localization. J Cell Biol 2004,165:203-211.

33. Czaplinski K, Mattaj IW: 40LoVe interacts with Vg1RBP/Veraand hnRNP I in binding the Vg1-localization element. RNA2006, 12:213-222.

34. Lewis RA, Gagnon JA, Mowry KL: PTB/hnRNP I is required forRNP remodeling during RNA localization in Xenopus oocytes.Mol Cell Biol 2008, 28:678-686.

35. Yabe T, Ge X, Pelegri F: The zebrafish maternal-effect genecellular atoll encodes the centriolar component sas-6 anddefects in its paternal function promote whole genomeduplication. Dev Biol 2007, 312:44-60.

36. Yabe T, Ge X, Lin R, Nair S, Runke G, Mullins MC, Pelegri F: Thematernal-effect gene cellular island encodes aurora B kinaseand is essential for furrow formation in the early zebrafishembryo. PLoS Genet 2009, 5:e1000518.

37. Vader G, Medema RH, Lens SM: The chromosomal passengercomplex: guiding Aurora-B through mitosis. J Cell Biol 2006,173:833-837.

38. Golling G, Amsterdam A, Sun Z, Antonelli M, Maldonado E,Chen W, Burgess S, Haldi M, Artzt K, Farrington S et al.:Insertional mutagenesis in zebrafish rapidly identifies genesessential for early vertebrate development. Nat Genet 2002,31:135-140.

39. Lyman Gingerich J, Westfall TA, Slusarski DC, Pelegri F: hecate, azebrafish maternal effect gene, affects dorsal organizerinduction and intracellular calcium transient frequency. DevBiol 2005, 286:427-439.

40. Lyman Gingerich J, Lindeman R, Putiri E, Stolzmann K, Pelegri F:Analysis of axis induction mutant embryos revealsmorphogenetic events associated with zebrafish yolkextension formation. Dev Dyn 2006, 235:2749-2760.

41. Nojima H, Shimizu T, Kim CH, Yabe T, Bae YK, Muraoka O, Hirata T,Chitnis A, Hirano T, Hibi M: Genetic evidence for involvement ofmaternally derived Wnt canonical signaling in dorsaldetermination in zebrafish. Mech Dev 2004, 121:371-386.

42. Bellipanni G, Varga M, Maegawa S, Imai Y, Kelly C, Myers AP,Chu F, Talbot WS, Weinberg ES: Essential and opposing roles of



zebrafish beta-catenins in the formation of dorsalaxial structures and neurectoderm. Development 2006,133:1299-1309.

43. Erter CE, Wilm TP, Basler N, Wright CV, Solnica-Krezel L: Wnt8 isrequired in lateral mesendodermal precursors for neuralposteriorization in vivo. Development 2001, 128:3571-3583.

44. Lekven AC, Thorpe CJ, Waxman JS, Moon RT: Zebrafish wnt8encodes two wnt8 proteins on a bicistronic transcript and isrequired for mesoderm and neurectoderm patterning. Dev Cell2001, 1:103-114.

45. Varga M, Maegawa S, Bellipanni G, Weinberg ES: Chordinexpression, mediated by Nodal and FGF signaling, isrestricted by redundant function of two beta-catenins in thezebrafish embryo. Mech Dev 2007, 124:775-791.

46. Reim G, Brand M: Maternal control of vertebrate dorsoventralaxis formation and epiboly by the POU domain protein Spg/Pou2/Oct4. Development 2006, 133:2757-2770.

47. Lachnit M, Kur E, Driever W: Alterations of the cytoskeleton in allthree embryonic lineages contribute to the epiboly defect ofPou5f1/Oct4 deficient MZspg zebrafish embryos. Dev Biol2008, 315:1-17.

48. Lunde K, Belting HG, Driever W: Zebrafish pou5f1/pou2,homolog of mammalian Oct4, functions in the endodermspecification cascade. Curr Biol 2004, 14:48-55.

49. Reim G, Mizoguchi T, Stainier DY, Kikuchi Y, Brand M: The POUdomain protein spg (pou2/Oct4) is essential for endodermformation in cooperation with the HMG domain proteincasanova. Dev Cell 2004, 6:91-101.

50.�

Holloway BA, Gomez de la Torre Canny S, Ye Y, Slusarski DC,Freisinger CM, Dosch R, Chou MM, Wagner DS, Mullins MC: Anovel role for MAPKAPK2 in morphogenesis during zebrafishdevelopment. PLoS Genet 2009, 5:e1000413.

This study identifies an unanticipated role for MAPKAPK2 and p38 MAPkinase in modulating a marginal constrictive force acting in zebrafishepiboly, providing novel molecular insight into this still poorly understoodtissue morphogenesis process.

51. Lukas SM, Kroe RR, Wildeson J, Peet GW, Frego L, Davidson W,Ingraham RH, Pargellis CA, Labadia ME, Werneburg BG:Catalysis and function of the p38 alpha, MK2a signalingcomplex. Biochemistry 2004, 43:9950-9960.

52. Giraldez AJ, Cinalli RM, Glasner ME, Enright AJ, Thomson JM,Baskerville S, Hammond SM, Bartel DP, Schier AF: MicroRNAsregulate brain morphogenesis in zebrafish. Science 2005,308:833-838.

53. Bushati N, Cohen SM: microRNA functions. Annu Rev Cell DevBiol 2007, 23:175-205.

54. Schier AF, Giraldez AJ: MicroRNA function and mechanism:insights from zebra fish. Cold Spring Harb Symp Quant Biol2006, 71:195-203.

55. Draper BW, McCallum CM, Moens CB: nanos1 is required tomaintain oocyte production in adult zebrafish. Dev Biol 2007,305:589-598.

56. Mishima Y, Giraldez AJ, Takeda Y, Fujiwara T, Sakamoto H,Schier AF, Inoue K: Differential regulation of germline mRNAs insoma and germ cells by zebrafish miR-430. Curr Biol 2006,16:2135-2142.

57.�

Kedde M, Strasser MJ, Boldajipour B, Oude Vrielink JA,Slanchev K, le Sage C, Nagel R, Voorhoeve PM, van Duijse J,Orom UA et al.: RNA-binding protein Dnd1 inhibits microRNAaccess to target mRNA. Cell 2007, 131:1273-1286.

This study demonstrates that the vertebrate-specific RNA binding proteinDnd, essential for germ line development in zebrafish and mouse, butpreviously of unknown molecular function, acts by blocking miRNA-mediated gene silencing in zebrafish germ cells and in cultured human


cells. Dnd binds to a U-rich site in the 30UTR of regulated transcripts that,in a still unknown manner, blocks miRNA binding.

58. Slanchev K, Stebler J, Goudarzi M, Cojocaru V, Weidinger G,Raz E: Control of dead end localization and activity–implications for the function of the protein in antagonizingmiRNA function. Mech Dev 2009, 126:270-277.

59. Weidinger G, Stebler J, Slanchev K, Dumstrei K, Wise C, Lovell-Badge R, Thisse C, Thisse B, Raz E: dead end, a novel vertebrategerm plasm component, is required for zebrafish primordialgerm cell migration and survival. Curr Biol 2003, 13:1429-1434.

60. Kuramochi-Miyagawa S, Kimura T, Ijiri TW, Isobe T, Asada N,Fujita Y, Ikawa M, Iwai N, Okabe M, Deng W et al.: Mili, amammalian member of piwi family gene, is essential forspermatogenesis. Development 2004, 131:839-849.

61. Cox DN, Chao A, Lin H: piwi encodes a nucleoplasmic factorwhose activity modulates the number and division rate ofgermline stem cells. Development 2000, 127:503-514.

62. Pal-Bhadra M, Bhadra U, Birchler JA: RNAi related mechanismsaffect both transcriptional and posttranscriptional transgenesilencing in Drosophila. Mol Cell 2002, 9:315-327.

63. Siegfried KR, Nusslein-Volhard C: Germ line control of femalesex determination in zebrafish. Dev Biol 2008, 324:277-287.

64. Slanchev K, Stebler J, de la Cueva-Mendez G, Raz E:Development without germ cells: the role of the germ line inzebrafish sex differentiation. Proc Natl Acad Sci U S A 2005,102:4074-4079.

65. Aravin AA, Sachidanandam R, Girard A, Fejes-Toth K, Hannon GJ:Developmentally regulated piRNA clusters implicate MILI intransposon control. Science 2007, 316:744-747.

66. Carmell MA, Girard A, van de Kant HJ, Bourc’his D, Bestor TH, deRooij DG, Hannon GJ: MIWI2 is essential for spermatogenesisand repression of transposons in the mouse male germline.Dev Cell 2007, 12:503-514.

67. Ciruna B, Weidinger G, Knaut H, Thisse B, Thisse C, Raz E,Schier AF: Production of maternal-zygotic mutant zebrafish bygerm-line replacement. Proc Natl Acad Sci U S A 2002,99:14919-14924.

68. Theodosiou NA, Xu T: Use of FLP/FRT system to studyDrosophila development. Methods 1998, 14:355-365.

69. Khakhar RR, Cobb JA, Bjergbaek L, Hickson ID, Gasser SM: RecQhelicases: multiple roles in genome maintenance. Trends CellBiol 2003, 13:493-501.

70. Xie J, Bessling SL, Cooper TK, Dietz HC, McCallion AS, Fisher S:Manipulating mitotic recombination in the zebrafish embryothrough RecQ helicases. Genetics 2007, 176:1339-1342.

71. Nasevicius A, Ekker SC: Effective targeted gene ‘knockdown’ inzebrafish. Nat Genet 2000, 26:216-220.

72. Draper BW, Morcos PA, Kimmel CB: Inhibition of zebrafish fgf8pre-mRNA splicing with morpholino oligos: a quantifiablemethod for gene knockdown. Genesis 2001, 30:154-156.

73. Doyon Y, McCammon JM, Miller JC, Faraji F, Ngo C, Katibah GE,Amora R, Hocking TD, Zhang L, Rebar EJ et al.: Heritabletargeted gene disruption in zebrafish using designed zinc-finger nucleases. Nat Biotechnol 2008, 26:702-708.

74. Meng X, Noyes MB, Zhu LJ, Lawson ND, Wolfe SA: Targetedgene inactivation in zebrafish using engineered zinc-fingernucleases. Nat Biotechnol 2008, 26:695-701.

75. Foley JE, Yeh JR, Maeder ML, Reyon D, Sander JD, Peterson RT,Joung JK: Rapid mutation of endogenous zebrafish genesusing zinc finger nucleases made by Oligomerized PoolENgineering (OPEN). PLoS ONE 2009, 4:e4348.


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