Novel markers identify nervous system components of the holothurian nervous system

Echinoderms occupy a key position in the evolution of deuterostomes. As such, the study of their nervous system can shed important information on the evolution of the vertebrate nervous system. However, the study of the echinoderm nervous system has lagged behind when compared to that of other invertebrates due to the lack of tools available. In this study, we tested three commercially available antibodies as markers of neural components in holothurians. Immunohistological experiments with antibodies made against the mammalian transcription factors Pax6 and Nurr1, and against phosphorylated histone H3 showed that these markers identified cells and fibers within the nervous system of Holothuria glaberrima. Most of the fibers recognized by these antibodies were co-labeled with the well-known neural marker, RN1. Additional experiments showed that similar immunoreactivity was found in the nervous tissue of three other holothurian species (Holothuria mexicana, Leptosynapta clarki and Sclerodactyla briareus), thus extending our findings to the three orders of Holothuroidea. Furthermore, these markers identified different subdivisions of the holothurian nervous system. Our study presents three additional markers of the holothurian nervous system, expanding the available toolkit to study the anatomy, physiology, development and evolution of the echinoderm nervous system.