AUTHOR=Imarazene Boudjema , Andouche Aude , Bassaglia Yann , Lopez Pascal-Jean , Bonnaud-Ponticelli Laure 

TITLE=Eye Development in Sepia officinalis Embryo: What the Uncommon Gene Expression Profiles Tell Us about Eye Evolution

JOURNAL=Frontiers in Physiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2017.00613

DOI=10.3389/fphys.2017.00613

ISSN=1664-042X

ABSTRACT=<p>In metazoans, there is a remarkable diversity of photosensitive structures; their shapes, physiology, optical properties, and development are different. To approach the evolution of photosensitive structures and visual function, cephalopods are particularly interesting organisms due to their most highly centralized nervous system and their camerular eyes which constitute a convergence with those of vertebrates. The eye morphogenesis in numerous metazoans is controlled mainly by a conserved Retinal Determination Gene Network (RDGN) including <italic>pax, six, eya</italic>, and <italic>dac</italic> playing also key developmental roles in non-retinal structures and tissues of vertebrates and <italic>Drosophila</italic>. Here we have identified and explored the role of <italic>Sof-dac, Sof-six1/2, Sof-eya</italic> in eye morphogenesis, and nervous structures controlling the visual function in <italic>Sepia officinalis</italic>. We compare that with the already shown expressions in eye development of <italic>Sof-otx</italic> and <italic>Sof-pax</italic> genes. <italic>Rhodopsin</italic> is the pigment responsible for light sensitivity in metazoan, which correlate to correlate visual function and eye development. We studied <italic>Sof-rhodopsin</italic> expression during retina differentiation. By <italic>in situ</italic> hybridization, we show that (1) all of the RDGN genes, including <italic>Sof-pax6</italic>, are expressed in the eye area during the early developmental stages but they are not expressed in the retina, unlike <italic>Sof-otx</italic>, which could have a role in retina differentiation; (2) <italic>Sof-rhodopsin</italic> is expressed in the retina just before vision gets functional, from stage 23 to hatching. Our results evidence a role of <italic>Sof-six1/2, Sof-eya</italic>, and <italic>Sof-dac</italic> in eye development. However, the gene network involved in the retinal photoreceptor differentiation remains to be determined. Moreover, for the first time, <italic>Sof-rhodopsin</italic> expression is shown in the embryonic retina of cuttlefish suggesting the evolutionary conservation of the role of <italic>rhodopsin</italic> in visual phototransduction within metazoans. These findings are correlated with the physiological and behavioral observations suggesting that <italic>S. officinalis</italic> is able to react to light stimuli from stage 25 of organogenesis on, as soon as the first retinal pigments appear.</p>