Neurosensory and neuromuscular organization in tube feet of the sea urchin Strongylocentrotus purpuratus

Abstract

Several behavioral and electrophysiological studies indicate that all classes of echinoderms, including Echinoidia, the class to which sea urchins belong, are photosensitive and exhibit complex behavioral responses to light or changes in light intensity. However, no discrete photosensitive structure has been identified in sea urchins. The purpose of this study was to provide new insights into eye evolution by determining whether distinct photosensory structures are present in adult sea urchins. Recently, we showed that the Strongylocentrotus purpuratus genome contains orthologs of many mammalian retinal genes and that these genes are expressed in tube feet, suggesting the presence of photoreceptor neurons. To determine whether this is so, we identified several features of tube feet that relate to a possible invertebrate phototransduction system. We show that rhabdomeric opsin is expressed severalfold higher within the disk region of the tube feet and is the most abundant opsin. Immunostaining identified βIII-tubulin-expressing cells at the periphery of disk in the vicinity of the synaptotagmin-expressing nerve fibers. We also showed that Pax6 expression in the disk was restricted to the periphery, where small clusters of putative sensory neurons reside. Our results reveal neuromuscular organization of the tube foot neuromuscular system. They further support earlier studies suggesting the presence of a photosensory system in tube feet.

Novel markers identify nervous system components of the holothurian nervous system

“…It is expressed during the gastrula stage and in the podia of adult sea urchins (Czerny and Busslinger 1995). In the adult tube feet, Pax6 is expressed exclusively in photoreceptors cells, suggesting that its main function, as a key transcription factor required for the differentiation of photosensory cells, is conserved in echinoderms (Agca et al 2011; Lesser et al 2011; Ullrich-Luter et al 2011). However, some of our results suggest that the epitopes being recognized by these two markers in H. glaberrima might differ from those of which they were designed against.…”

Calbindin-D32k Is Localized to a Subpopulation of Neurons in the Nervous System of the Sea Cucumber Holothuria glaberrima (Echinodermata)

“…Our findings provide new markers for a subpopulation of neurons and fibers in the echinoderm nervous system. The availability of these new markers make feasible the study of the evolutionary aspects of the calcium-binding proteins family, as has been done recently with other gene family, the retinal genes in S. purpuratus [26]. Furthermore, we identified the presence of calbindin-D32k in H. glaberrima and L. variegatus , supporting its presence in at least two classes of echinoderms Our data also supports the evolutionary conservation of the calbindin subfamily, which seems to have evolved from two primitive EF-hand domain-containing CBP.…”

Synaptotagmin1 is required for spindle stability and metaphase-to-anaphase transition in mouse oocytes

“…For example, βIII-tubulin was expressed at the periphery of the disk in the vicinity of Syt-expressing nerve fibers in tube feet of the sea urchin Strongylocentrotus purpuratus. 35 Synaptotagmin 9 is a member of Syts, and it was localized to the pericentriolar ERC (endocytic recycling compartment), which was clustered around the centrosome. Furthermore, Syt 9 was co-localized with tubulin at the MTOC and remained at tubulin clusters after taxol treatment of RBL (rat basophilic leukemia) cells.…”