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Rab8B GTPase and Junction Dynamics in the Testis

Population Council, Center for Biomedical Research, New York, New York 10021

Address all correspondence and requests for reprints to: Dolores D. Mruk, Ph.D., Population Council, Center for Biomedical Research, 1230 York Avenue, New York, New York 10021. E-mail: mruk{at}popcbr.rockefeller.edu.

Throughout spermatogenesis, germ cells migrate from the basal to the adluminal compartment while remaining attached to Sertoli cells via actin-based adherens and intermediate filament-based anchoring junctions. However, the events that trigger deadhesion and adhesion remain largely unknown. As part of our continued effort in elucidating the mechanism of germ cell movement, we have examined the role of Rab8B, a GTPase probably participating in intracellular trafficking events at the site of the adherens junction. By RT-PCR Rab8B mRNA was found in the brain, testis, heart, kidney, and spleen. Immunohistochemical studies revealed that Rab8B was concentrated predominantly in the basal compartment, localizing to a similar site at which immunoreactive E-cadherin was found. Additional experiments demonstrated that Rab8B associated with the actin, intermediate filament, and microtubule cytoskeletal networks. When Sertoli cells were cultured at high density or germ cells were cocultured with Sertoli cells, Rab8B increased significantly during junction assembly. Moreover, inclusion of germ cell-conditioned medium in Sertoli cell cultures resulted in stimulation of Rab8B expression. Conversely, treatment of adult rats with 1-(2,4-dichlorobenzyl)-indazole-3-carbohydrazide reduced Rab8B mRNA and protein levels, coinciding with the time of germ cell loss from the epithelium. Taken collectively, these studies suggest that Rab8B participates in adherens junction dynamics in the testis.

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