Seminario di gruppo in aula- P.Valeria;C.Paolo; A.Simona ( Coordinatrice Prof.ssa Albanese Ninfa)

Realizzato da: Airò Simona

Cina’ Paolo

Prestigiacomo Valeria

Articoli ScientificiArticoli Scientifici:-Genetic and Developmental Mechanisms Underlying the Formation of the Drosophila Compound Eye Maria Tsachaki and Simon G. Sprecher*-Retinal determination genes function along with cell-cell signals to regulate Drosophila eye development Nicholas E. Baker and Lucy C. Firth-Pattern formation in the Drosophila eye disc Jean-Yves Roignant and Jessica E. Treisman*

Seminario in aula: P.Valeria; C.Paolo;A.Simona-UNIPA

Fig. 1. A: Picture of the compound eye of Drosophila. The compound eye consists of 750–800 individual subunits, the ‘‘ommatidia.’’ B: Confocal image of a larval eye-antennal imaginal disc. The disc is subdivided into the ‘‘antennal part’’ (anterior, to the left of the image) and the ‘‘eye’’ part (posterior, to the right of the image). The cells already determined as neurons express the neuronal marker Elav (red). The cells that are specified as photoreceptors express the photoreceptor-specific marker Chaoptin (Chp, green). All the cell nuclei are stained with DAPI (blue). MF, Morphogenetic furrow.

Fig. 2. A: The genes comprising the Retinal Determination Network (RDN). The dotted linesrepresent physical interactions that have not been confirmed in vivo. The genes that control cellproliferation are shown in green and those that control retinal formation in blue. The genes forwhich the relation with the other members has not been determined by genetic interactions areshown in orange (for details see the text). B: Adult fly head exhibiting complete absence ofeyes, caused by mutation in the RDN gene eyes absent (eya). C: Pupa showing ectopic eye formationafter misexpression of eyeless (ey) using the dpp-Gal4 driver line. The arrowheads pointtowards ectopic


Il Solco Morfogenetico (MF) si forma al margine posteriore del disco imaginale, e progredisce in avanti verso la parte anteriore dell’epitelio.

IL MOVIMENTO DEL SOLCO DIPENDE DA HEDGEHOG E DA DECAPENTAPLEGIC



HEDGEHOG è espresso dalle cellule posteriori al MF ed induce l’espressione di DECAPENTAPLEGIC nel solco.

Figure 2. Hh induces long-range and short-range secondary signals that control the precise positionof the MFHh acts over a short range to induce the expression of Dpp, which diffuses over a long rangeto turn off hth and turn on hairy, establishing a preproneural domain (PPN). Hh and Dpp alsoinduce the expression of Delta, a transmembrane ligand that acts on adjacent cells to turn offhairy and allow ato expression, initiating photoreceptor differentiation.Roignant and Treisman Page 17Int J

Gli ommatidi sono formati da 8 PRs: 6 esterni e 2 interni

•I PRs esterni sono omologhi dei bastoncelli nei vertebrati

•I PRs interni sono gli omologhi dei coni nei vertebrati

Il PR R7 esprime la rodopsina UV-sensibileIl PR R8 esprime Rh5 blu sensibile o Rh6 verde sensibile


Fig. 6. A: Schematic representation of ‘‘pale’’ and ‘‘yellow’’ ommatidia. Pale ommatidia express Rh3 in R7 and Rh5 in R8 and yellow ommatidiaexpress Rh4 in R7 and Rh6 in R8. B: Confocal image of a compound eye, showing the mosaic of pale and yellow ommatidia. The pale R8 expressRh5 (red) and the yellow Rh6 (green). The cytoplasm of all the ommatidia is stained with phalloidin that binds to F-actin (blue). C: The choicebetween pale and yellow ommatidia. A part of the R7 starts to express spineless (ss) stochastically, which defines these R7 as yellow. Subsequently,ss sends a signal to the overlying R8 to express warts, which promotes rh6 expression. The R8 that do not turn on warts expression express melt,which activates rh5 expression. warts and melt suppress each other’s expression. D: Overview of the subtype specification of R7 and R8 PRs.


La differenziazione tra ommatidi Yellow e Pale è mediato da R7 che esprime SPINGLESS (SS)

Gli ommatidi Yellow sono il 70% mentre gli ommatidi Pale sono il 30%

SS induce il destino Yellow, ORTHODENTICLE (OTD) il destino Pale


I precursori cellulari pluripotenti che risiedono nel disco imaginale dell’occhio sono trasformati in cellule altamente

specializzate dentro il MF.

Parecchie cascate di segnalazione partecipano in questo processo.

come ad es. EGFR e Notch che regolano il segnale di Hh


Principali protagonisti nello sviluppo dell’occhio

Geni effettori differenziamento

Fattori trascrizionali attivati da unno stimolo esterno

Geni Retinal Determination ( Geni regolatori master)

Sviluppo spazio-temporale specifico


Geni RD

Eyless, sine oculis, eyes absent, teashirt.

Pax 6 omologo di eyless.


Attivazione della trascrizione di hh


Organizzazione dei cluster all’interno di ciascuna colonna

Figure 3. Inhibitory signals control cluster spacing and R8

specification(A) shows that spacing of

intermediate groups is controlled by inhibitory

signals from clustersin the preceding column,

including Sca and a second factor downstream of EGFR

signaling.(B) shows the process of

restriction of Ato expression within the MF from a continuous stripeof cells to intermediate

groups, 3-cell R8 equivalence groups, and

single R8 cells. R8 selectionrequires local lateral

inhibition mediated by Notch and Sca.


Figure 4. Sequential recruitment of ommatidial cells is controlled by the short-range ligands Spiand DlSpi promotes the differentiation of photoreceptors R2, 5, 3, 4, 1 and 6. It also induces theexpression of Dl, which acts together with Spi and Boss to promote R7 differentiation, togetherwith Spi to promote cone cell differentiation, and alone to promote primary pigment celldifferentiation. Cells are added sequentially because Spi and Dl can only act over a shortdistance.

La sequenziale differenziazione all’interno di ciascun gruppo dipende dal raggio di segnalazione Seminario in aula: P.Valeria;

C.Paolo;A.Simona-UNIPA

Figure 5. Hh and Spi signals are transported down the photoreceptor axons to organize the targetregionHh promotes the final division of lamina precursor cells (LPC) posterior to the lamina furrow(LF), and through Sim, their association with photoreceptor axons. Hh also induces the LPCsto express Dac, which activates expression of the EGFR, allowing them to respond to Spi. Cellsthat respond to Hh by expressing Dac and EGFR are colored yellow. Spi then promotes LPCdifferentiation adjacent to retinal axons. Cells that respond to Spi by expressing Elav arecolored red. Release of the same signals from the cell body and the axons coordinatesmorphogenesis of the eye and the lamina.

I fotorecerettori coordinano la differenziazione delle loro cellule bersaglio nelle lamina


Conclusioni

• Ruolo fondamentale dei cicli di autoregolazione positivi

• Intervallo di tempo nella distribuzione dei segnali

• Uso degli stessi segnali in occhio e cervello


Date post:	15-Apr-2017
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Seminario di gruppo in aula- P.Valeria;C.Paolo; A.Simona ( Coordinatrice Prof.ssa Albanese Ninfa)

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