Ichimura, K., Fukuyo, Y., Nakamura, T., Powell, R., Sakai, T., Janknecht, R., and Obara, T. (2013) Developmental Localization of Nephrin in Zebrafish and Medaka Pronephric Glomerulus. The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society. 61(4):313-324.
Slit diaphragm (SD) is a highly specialized intercellular junction between podocyte foot processes and plays a crucial role in the formation of the filtration barrier. In this study, we examined the developmental localization of Nephrin, an essential component of SD, in the pronephric glomerulus of zebrafish and medaka. In the mature glomerulus of both fish, Nephrin is localized along the glomerular basement membrane like in mammals, indicating that Nephrin is localized at the SD. Interestingly, Nephrin was detected already in immature podocytes before the SD and foot processes start to form in both fish. Nephrin was localized along the cell surface of immature podocytes, but as different localization patterns. In zebrafish, Nephrin signal bordered the lateral membrane of podocytes, which were columnar in shape as are in rat immature podocytes. However, in medaka immature podocytes, Nephrin was localized in a punctate pattern among podocyte cell bodies. These findings suggest that Nephrin is needed to be integrated to the membrane before the formation of SD and then move to the proper site to form SD. Furthermore, a podocyte-specific marker, such as Nephrin, should be a useful tool for the future analysis of pronephric glomerular development in fish mutants and morphants.