Glass confers rhabdomeric photoreceptor identity inDrosophila, but not across all metazoans

Abstract

Across metazoans, visual systems employ different types of photoreceptor neurons to detect light. These include rhabdomeric PRs, which exist in distantly related phyla and possess an evolutionarily conserved phototransduction cascade. While the development of rhabdomeric PRs has been thoroughly studied in the fruit fly Drosophila melanogaster, we still know very little about how they form in other species. To investigate this question, we tested whether the transcription factor Glass, which is crucial for instructing rhabdomeric PR formation in Drosophila, may play a similar role in other metazoans. Glass homologues exist throughout the animal kingdom, indicating that this protein evolved prior to the metazoan radiation. Interestingly, our work indicates that glass is not expressed in rhabdomeric photoreceptors in the planarian Schmidtea mediterranea nor in the annelid Platynereis dumerilii. Combined with a comparative analysis of the Glass DNA-binding domain, our data suggest that the fate of rhabdomeric PRs is controlled by Glass-dependent and Glass-independent mechanisms in different animal clades.

The brachyceran de novo gene PIP82, a phosphorylation target of aPKC, is essential for proper formation and maintenance of the rhabdomeric photoreceptor apical domain in Drosophila

“…As we have described, our results have demonstrated that PIP82 is regulated by a conserved set of transcription factors for rhabdomeric photoreceptor differentiation in insects, found in both open or fused rhabdom configurations [ 19 , 21 , 65 ]. Our data demonstrated the key regulator is the zinc finger protein Glass and a feed forward loop that requires the photoreceptor specific transcription homeodomain transcription factor Pph13 for maximum expression [ 30 ].…”

“…Subsequently, we identified PIP82 in two different transcriptome studies designed to identify genes required for the differentiation of Drosophila photoreceptors [ 24 , 25 ]. In particular, our transcriptome analyses suggested that PIP82 is part of the Glass-Pph13 dependent transcriptional cascade that is essential for photoreceptor cell development [ 19 , 25 , 26 ]. Recent studies revealed that Glass has two temporal roles with respect to retina development, specification and differentiation [ 19 , 25 , 26 ].…”

“…In particular, our transcriptome analyses suggested that PIP82 is part of the Glass-Pph13 dependent transcriptional cascade that is essential for photoreceptor cell development [ 19 , 25 , 26 ]. Recent studies revealed that Glass has two temporal roles with respect to retina development, specification and differentiation [ 19 , 25 , 26 ]. With respect to differentiation, the function of Glass is aided by the Glass mediated transcription of the homeodomain containing transcription factor Pph13 [ 25 , 27 , 28 ].…”

“…Here we evaluate an orphan protein, PIP82, which was nominally mentioned as a potential component or downstream effector molecule of phototransduction [ 18 ]. Our studies indicate PIP82 is a downstream effector molecule of the conserved Glass/Pph13 transcriptional pathway required for rhabdomeric photoreceptor differentiation among Pancrustaceans [ 19 – 21 ]. Nonetheless, the gene is only present in a select group of insects.…”