Identification of aquaporins in eggs and early embryogenesis of the sea urchin Paracentrotus lividus.

Sea urchins are echinoderms, marine invertebrates found at the base of the deutorostome lineage, which show separate sexes and are external spawners. In the sea urchin, efficient regulation of water homeostasis is essential for many biological processes such as cellular respiration, normal fertilization and correct embryo growth. In order to clarify some of these processes, the present study reports on the identification and function of aquaporin proteins in the sea urchin. Our results show, by immunoblot, immunoelectron microscopy and immunofluorescence analysis, the presence of aquaporin1- and aquaporin3-like proteins in virgin eggs and in early embryogenesis of Paracentrotus lividus and, by using known inhibitors of aquaporin functions, the functional and relevant role of aquaporin-3 in the fertilization process. AQP3 in particular seems to play a crucial role in high velocity water flux formations involved in the detachment of the vitelline layer during the slow block of polyspermy, while the presence of AQP1 and the increase of AQP3 in the first phase of the P. lividus developmental cycle, suggest their involvement in the appropriate homeostasis for embryo development.