Retinal differentiation in Drosophila

Abstract

Drosophila eye development has been extensively studied, due to the ease of genetic screens for mutations disrupting this process. The eye imaginal disc is specified during embryonic and larval development by the Pax6 homolog Eyeless and a network of downstream transcription factors. Expression of these factors is regulated by signaling molecules and also indirectly by growth of the eye disc. Differentiation of photoreceptor clusters initiates in the third larval instar at the posterior of the eye disc and progresses anteriorly, driven by the secreted protein Hedgehog. Within each cluster, the combined activities of Hedgehog signaling and Notch-mediated lateral inhibition induce and refine the expression of the transcription factor Atonal, which specifies the founding R8 photoreceptor of each ommatidium. Seven additional photoreceptors, followed by cone and pigment cells, are successively recruited by the signaling molecules Spitz, Delta, and Bride of sevenless. Combinations of these signals and of intrinsic transcription factors give each ommatidial cell its specific identity. During the pupal stages, Rhodopsins are expressed, and the photoreceptors and accessory cells take on their final positions and morphologies to form the adult retina. Over the past few decades, the genetic analysis of this small number of cell types arranged in a repetitive structure has allowed a remarkably detailed understanding of the basic mechanisms controlling cell differentiation and morphological rearrangement.

Expression and light-triggered movement of rhodopsins in the larval visual system of mosquitoes

“…As a result, the posterior regions contain more mature ommatidial units than the anterior regions. The process appears similar to the extensively studied morphogenesis of the adult Drosophila eye (Treisman, 2013). During ommatidial differentiation, Aaop7 is briefly expressed in ommatidial units at the anterior edge of developing compound eye.…”

The transcription factor glass links eye field specification with photoreceptor differentiation in Drosophila

“…In this sense, we were curious to see whether Ato regulates glass, both because of its expression pattern right before the onset of Glass expression and because of the importance of Ato to induce neural cell fate in PR precursors ( Fig. S11; Jarman et al, 1994;Aerts et al, 2010;Treisman, 2013). However, we found that Glass is still expressed in ato mutant clones in the third instar eye disc, suggesting that both Glass and Ato work in parallel, but independently (Fig.…”

“…At this stage, the RDN member So directly activates the proneural gene ato at the morphogenetic furrow, and Ato induces the formation of PR precursors. Although extensive information is available on the activation of ato, and on how Ato specifies PR precursors to become neurons (Zhang et al, 2006;Tanaka-Matakatsu and Du, 2008;Aerts et al, 2010;Treisman, 2013;Jusiak et al, 2014), little is known about how these neurons become mature PRs. We propose that activation of glass by either the RDN or Ato should be a key step in this process.…”

“…By the end of the third instar, cells contract apically, forming a transient groove termed the morphogenetic furrow, which sweeps across the eye disc. After the passage of the morphogenetic furrow, the proneural transcription factor Atonal (Ato) triggers specification of the R8 PR precursors, which sequentially recruit other PR precursors into the developing ommatidia by EGFR signalling: first R2/R5, then R3/R4, R1/R6 and finally, R7 (Ready et al, 1976;Treisman, 2013). A number of genes that are differentially expressed in the distinct PR subtypes control their subtype identity, and regulate how these cells develop during metamorphosis into adult PRs (Mollereau and Domingos, 2005;Tsachaki and Sprecher, 2012;Treisman, 2013).…”

ESCRT-0 complex modulates Rbf-mutant cell survival by regulating Rhomboid endosomal trafficking and EGFR signaling

“…Photoreceptor differentiation in the developing eye initiates in the morphogenetic furrow (Treisman, 2013). Anterior to the morphogenetic furrow, cells are undifferentiated and asynchronously proliferating.…”