Diversity of Light Sensing Molecules and Their Expression During the Embryogenesis of the Cuttlefish (Sepia officinalis)

Abstract

Eyes morphologies may differ but those differences are not reflected at the molecular level. Indeed, the ability to perceive light is thought to come from the same conserved gene families: opsins and cryptochromes. Even though cuttlefish (Cephalopoda) are known for their visually guided behaviors, there is a lack of data about the different opsins and cryptochromes orthologs represented in the genome and their expressions. Here we studied the evolutionary history of opsins, cryptochromes but also visual arrestins in molluscs with an emphasis on cephalopods. We identified 6 opsins, 2 cryptochromes and 1 visual arrestin in Sepia officinalis and we showed these families undergo several duplication events in Mollusca: one duplication in the arrestin family and two in the opsin family. In cuttlefish, we studied the temporal expression of these genes in the eyes of embryos from stage 23 to hatching and their expression in two extraocular tissues, skin and central nervous system (CNS = brain + optic lobes). We showed in embryos that some of these genes (Sof_CRY 6 , Sof_reti-1, Sof_reti-2, Sof_r-opsin1 and Sof_v-arr) are expressed in the eyes and not in the skin or CNS. By looking at a juvenile and an adult S. officinalis, it seems that some of these genes (Sof_r-opsin1 and Sof_reti1) are used for light detection in these extraocular tissues but that they setup later in development than in the eyes. We also showed that their expression (except for Sof_CRY 6) undergoes an increase in the eyes from stage 25 to 28 thus confirming their role in the ability of the cuttlefish embryos to perceive light through the egg capsule. This study raises the question of the role of Sof_CRY 6 in the developing eyes in cuttlefish embryos and the role and localization of xenopsins and r-opsin2. Consequently, the diversity of molecular actors involved in light detection both in the eyes and extraocular tissues is higher than previously known. These results open the way for studying new molecules such as those of the signal transduction cascade.

Duplication and losses of opsin genes in lophotrochozoan evolution

“…Our results substantially clarify the evolution of the opsin genes in lophotrochozoans over 600 million years, suggesting a diverging evolutionary history of opsins in this clade (Figure 3). Overall, our phylogenetic tree supports the sister relationship of c-opsins and Group-4 opsins, with r-opsins being sister to this clade, similarly to previous works (Yoshida et al 2015; Vöcking et al 2017; Rawlinson et al 2019; Bonadè et al 2020; Fleming et al 2020). Noteworthy, our tree supports the monophyly of xenopsins and c-opsins similarly to some of the studies (Yoshida et al 2015; Vöcking et al 2017) but differently from others (Ramirez et al 2016; Rawlinson et al 2019; Bonadè et al 2020).…”

“…Previous works have investigated the opsin evolution in lophotrochozoans focusing mostly on individual species or specific clades (Passamaneck et al 2011; Gühmann et al 2015; Yoshida et al 2015; Ramirez et al 2016; Bok et al 2017; Vöcking et al 2017; Rawlinson et al 2019; Bonadè et al 2020; Döring et al 2020); as consequence, the complete view of the evolution and the long-term dynamics of opsin genes in this clade remains poorly understood. Here, we study the evolution of opsin genes in 11 lophotrochozoan phyla using a phylogenomics approach.…”

A single-cell atlas of bobtail squid visual and nervous system highlights molecular principles of convergent evolution

“…We identified two closely related populations of photoreceptors (Photoreceptor_r1 and _r2) based on their expression of photosensitive molecules, phototransduction cascade effectors (Gq, PLC, Arrestin) and retinol recycling markers (Figure 2C). Of the six putative E. berryi photosensitive GPCRs that we identified by phylogenetic analysis – two rhabdomeric opsins (r-opsin1 and 2), two retinochromes (retinochrome 1 and 2) and two xenopsins (xenopsin1 and xenopsin2) (Figure S3B, (Bonadè et al, 2020)) – only the r-opsins and retinochrome-2 showed detectable retinal expression in both scRNA-seq and bulk RNA-seq (Figure S3B). We identify the Photoreceptor_r2 subpopulation as the primary photoreceptor type based on its high expression of r-opsin2, the primary photosensitive molecule in cephalopods (Bonadè et al, 2020).…”

“…First, we observed two populations of photoreceptors, one of which expressed a second r-opsin gene. Although two r-opsin genes have been described in cephalopods, expression of more than one r-opsin in the retina has not been described (Bonadè et al, 2020). The presence of two photoreceptor populations with multiple opsin molecules is curious as cephalopods are not known to rely on color vision, but rather to detect differences in the polarization of light (Marshall and Messenger, 1996; Mäthger et al, 2006; Messenger et al, 1973; Saidel et al, 2005).…”

“…Of the six putative E. berryi photosensitive GPCRs that we identified by phylogenetic analysis -two rhabdomeric opsins (r-opsin1 and 2), two retinochromes (retinochrome 1 and 2) and two xenopsins (xenopsin1 and xenopsin2) (Figure S3B, (Bonadè et al, 2020)) -only the r-opsins and retinochrome-2 showed detectable retinal expression in both scRNA-seq and bulk RNA-seq (Figure S3B). We identify the Photoreceptor_r2 subpopulation as the primary photoreceptor type based on its high expression of r-opsin2, the primary photosensitive molecule in cephalopods (Bonadè et al, 2020). We find that r-opsin2 is also expressed in non-visual tissues in E. berryi (Figure S3C, Figure 2C), consistent with r-opsin expression in other cephalopods (Kingston and Cronin, 2016;Kingston et al, 2015aKingston et al, , 2015b.…”