The document summarizes key aspects of eye development in Drosophila melanogaster. It discusses the genetic networks that pattern the eye imaginal disc, including the retinal determination genes. It describes how the morphogenetic furrow forms and progresses across the disc, mediated by Hedgehog and Decapentaplegic signaling. Individual ommatidial units then form in a sequential, spatially regulated process relying on short-range signaling by Spitz and Delta. Photoreceptor axons also help coordinate lamina development through long-range transport of Hedgehog and Spitz. The stochastic selection of pale versus yellow ommatidial subtypes is regulated by genes like Spineless in the R7 photoreceptor.

1. 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*
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2. 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 lines
represent physical interactions that have not been confirmed in vivo. The genes that control cell
proliferation are shown in green and those that control retinal formation in blue. The genes for
which the relation with the other members has not been determined by genetic interactions are
shown in orange (for details see the text). B: Adult fly head exhibiting complete absence of
eyes, caused by mutation in the RDN gene eyes absent (eya). C: Pupa showing ectopic eye formation
after misexpression of eyeless (ey) using the dpp-Gal4 driver line. The arrowheads point
towards ectopic
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3. 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
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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 position
of the MF
Hh acts over a short range to
induce the expression of Dpp,
which diffuses over a long range
to turn off hth and turn on hairy,
establishing a preproneural domain
(PPN). Hh and Dpp also
induce the expression of Delta, a
transmembrane ligand that acts on
adjacent cells to turn off
hairy and allow ato expression,
initiating photoreceptor
differentiation.
Roignant and Treisman Page 17
Int J

5. 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-sensibile
Il PR R8 esprime Rh5 blu sensibile o Rh6 verde sensibile
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6. Fig. 6. A: Schematic representation of
‘‘pale’’ and ‘‘yellow’’ ommatidia. Pale
ommatidia express Rh3 in R7 and Rh5
in R8 and yellow ommatidia
express 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 express
Rh5 (red) and the yellow Rh6 (green).
The cytoplasm of all the ommatidia is
stained with phalloidin that binds to F-
actin (blue). C: The choice
between 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.
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7. 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
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8. 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
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9. 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
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10. Geni RD
Eyless, sine oculis, eyes absent, teashirt.
Pax 6 omologo di eyless.
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11. Attivazione della trascrizione di hh
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12. 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 clusters
in 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 stripe
of cells to intermediate
groups, 3-cell R8
equivalence groups, and
single R8 cells. R8 selection
requires local lateral
inhibition mediated by
Notch and Sca.
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13. Figure 4. Sequential recruitment of ommatidial cells is controlled by the short-range ligands Spi
and Dl
Spi promotes the differentiation of photoreceptors R2, 5, 3, 4, 1 and 6. It also induces the
expression of Dl, which acts together with Spi and Boss to promote R7 differentiation, together
with Spi to promote cone cell differentiation, and alone to promote primary pigment cell
differentiation. Cells are added sequentially because Spi and Dl can only act over a short
distance.
La sequenziale differenziazione all’interno di ciascun gruppo
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14. Figure 5. Hh and Spi signals are
transported down the photoreceptor
axons to organize the target
region
Hh 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 LPCs
to express Dac, which activates
expression of the EGFR, allowing them to
respond to Spi. Cells
that respond to Hh by expressing Dac and
EGFR are colored yellow. Spi then
promotes LPC
differentiation adjacent to retinal axons.
Cells that respond to Spi by expressing
Elav are
colored red. Release of the same signals
from the cell body and the axons
coordinates
morphogenesis of the eye and the
lamina.
I fotorecerettori coordinano la differenziazione delle loro cellule
bersaglio nelle lamina
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15. Conclusioni
• Ruolo fondamentale dei cicli di
autoregolazione positivi
• Intervallo di tempo nella distribuzione dei
segnali
• Uso degli stessi segnali in occhio e cervello
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