ANIMAL DEVELOPMENT

Chapter 47

I) Stages of Early Embryonic Development 1) preformation vs.

epigenesis

A) Fertilization 1) The acrosomal

reactiona) enzymes released by acrosomeb) acrosomal process penetrates the jelly coat

c) proteins on tip of process bind to receptors on vitelline layer, just outside of plasma membranec1) lock and key: only sperm from that species will fit

d) membrane of sperm fuses with membrane of eggd1) ion channels open in egg, allowing Na into eggd2) this polarizes egg, blocking entry of any more sperm = fast block to polyspermy

2) The Cortical Reactiona) egg releases Ca2+ from ER at site of sperm entryb) this spreads throughout cytosol, causing release of more Ca2+

c) Ca causes cortical granules to fuse with membrane and release contents into perivitelline space

d) vitelline layer separates from membrane and hardens, creating a fertilization envelope = slow block to polyspermy

http://www.youtube.com/watch?v=9zv3TRlctTY

http://worms.zoology.wisc.edu/urchins/phasecal.html

3) Activation of the egga) transport of H+ out raises pH, allowing an increase in metabolism and protein synthesisa1) some protein synthesis occurs even without nucleus, so mRNA was stockpiled in egg

a2) activation can be artificial and without nucleus, showing that molecules involved in activation were also present in cytoplasm

4) Fertilization in mammalsa) similar to invertebratesb) zona pellucida surrounds the egg, which hardens after the cortical reaction to be the slow block to polyspermy

B) Cleavage 1) rapid division of

embryo with no cellular growth between divisionsa) small cells called blastomeres

2) the following occurs except for mammalsa) High amounts of yolk are stored in vegetal pole

b) animal pole has little yolk, and divides faster

c) in amphibians, animal pole is dark gray. c1) cytoplasm rotates toward point of sperm entry, leaving a grey crescent

**sperm can only enter in the animal pole along the animal/vegetal border

3) first two rounds of cleavage occur along animal-vegetal pole axis

4) next round divides perpendicular to this, mainly in animal pole because vegetal pole is too thick.a) holoblastic cleavage: complete division of cells(sea urchin and frog)

b) meroblastic cleavage:b1) incomplete division from large concentration of yolk* birds: yolk is an egg cell, with small disc of yolk free cytoplasm at top of animal pole.

5) Morula: solid ball of cells

6) blastula: has a fluid filled cavity called blastocoel

C) Gastrulation 1) production of 3

(germ) cell layersa) ectoderm: skin, hair, nervous systemb) endoderm: digestive tractc) mesoderm: muscles, bones, blood

2) gastrulation of sea urchina) invagination: mesenchyme cells at vegetal pole migrate toward animal pole and pull vegetal plate up

b) pouch formed is called archenteron (primitive gut)

c) blastopore: opening of archenteron

3) gastrulation in froga) invagination of cells forms a dorsal lip at the blastopore (at gray crescent)

b) cells migrate around embryo toward blastopore, until a full circle is formed, creating a yolk plug.

http://www.youtube.com/watch?v=ojqXV062CNIanimation

D) Organogenesis 1) Notochord

a) dorsal mesoderm condenses

2) Neural tubea) dorsal ectoderm folds downward and pinches off, creating a tube

video

3) Somitesa) clusters of mesoderm that surround the neural tube and turn into vertebrae/muscles

E) Amniote embryos 1) amniotic sac: fluid

filled sac surrounding the embryo

2) birds a) early cleavage

creates a blastodisc, a cap of cells on the yolk that create the embryo

a1) epiblasta2) hypoblasta3) blastocoel

b) cells of upper layer roll down and into blastocoel

b1) forms a primitive streak on top of blastodisc (shows anterior-posterior alignment)

b2) embryo only comes from epiblast

b3) germ layers outside of embryo become extra -embryonic membranes

* yolk sac: nutrients * amnion: fluid filled

sac around embryo * allantois: uric acid

storage/ gas exchange

* chorion: shock support/ gas exchange

3) Mammals a) blastocyst: circle of

cells with an inner cell mass

b) inner cell mass: cells that will become embryo and extra-embryonic membranes

c) trophoblast: outer cells that form fetal half of placenta

d) follows similar gastrulation as birdd1) epiblast and hypoblast form

d2) yolk sac forms and creates blood cells that migrate into embryod3) allantois turns into umbilical chord

II) Cellular and Molecular Basis of Differentiation A) changes in cell

shape, position, and adhesion1) microtubules shorten or elongate to change the shape of the cell

2) Convergent extensiona) cells wedge in between each other, making the region narrower, but longer

3) Extracellular matrixa) glycoproteins secreted by cells to control their, and other cells’, movements

4) Cell Adhesion Molecules(CAMs)a) glycoproteins on the surface of a cell that bind to other CAMs

b) cadherins: CAM that requires Ca to function properly

B) Fate Mapping 1) cells and their

progeny can be traced using dyes or other markers

C) Cytoplasmic Determinants 1) Polarity and body

plana) bilaterally symmetrical organisms have:a1) anterior-posterior axisa2) dorsal-ventral axisa3) left and right sides

b) established by positioning of materials in the egg

2) Restriction of cellular potencya) cleavage can divide materials evenly or unevenly

a1) inclusion of grey crescent allows full development

D) Inductive signals drive differentiation 1) The “organizer” of

Spemann and Mangolda) found that the dorsal lip of blastopore controls neurulation

a1) called this region the “primary organizer”