Perceive the world with five arms: opsin diversity and fonctions in the common sea star

In eumetazoans, light is mainly detected through photosensitive
proteins, the opsins, which are involved in both vision and nonvisual
photoreception. Advances in comparative genomics
transformed our understanding of the evolution of opsin-based
photoreception. A picture emerged of a core set of opsin-based
signalling pathways that can be traced back to the common
ancestor of Bilateria, with opsin orthologs being identified in an
increasingly
wide range of phyla! Although echinoderms have neither brain
nor eyes (sensu stricto),
most of the investigated species are light sensitive and up to 7
bilaterian-type opsin groups were identified in these organisms.
Based on transcriptome and genome data, this research focused
on the opsin diversity of the common European sea star Asterias
rubens. In addition, the sensitivity of A. rubens to monochromatic
light was also investigated based on phototactism and color
change assays. The results confirm (i) the ability of the common
sea star to perceive light using both ocellar and extra-ocellar
opsin-based photoreception and (ii) the co-occurrence of various
opsin types, but also (iii) emphasise the complexity of light
perception in these marine invertebrates. Overall, this research
contributes to the understanding of opsin-based extraocular
photoreception in echinoderms, giving precious insights on opsin
evolution and functions, and photoreceptor cell organisation in
these enigmatic organisms that bridge the gap between the
extensively studied vertebrates and protostomian model species.