MICROTUBULES ARE ORIENTED WITH THEIR MINUS-ENDS DIRECTED APICALLY BEFORE TIGHT JUNCTION FORMATION IN RAT SERTOLI CELLS

We have examined the polarity of microtubules in Sertoli cells of the seminiferous epithelium during testicular development to test the hypo thesis that microtubules change their polarity during tight junction f ormation. Microtubules in a number of polarized epithelial cells, incl uding Sertoli cells, are oriented with their minus-ends directed towar d the apical surface of the cell. Indirect evidence from cultured epit helial cell models suggests that this orientation may be achieved duri ng the relocation of centrioles, reorganization of microtubules, and r epositioning of the Golgi that occurs during tight junction formation. Using the microtubule hook decoration technique, we have determined t he polarity of Sertoli cell microtubules at 5 and 15 days postnatally, prior to the establishment of the tight junctional complex of the blo od testis barrier at 19 days. Our results indicate that, although cent rioles and the Golgi apparatus migrate from an intranuclear location a t 5 days to a supranuclear location by 15 days, the minus-ends of micr otubules are already directed toward the apical surface of the cell by 5 days of age. These data indicate that the establishment of the apic ally directed minus-end orientation of microtubules of mature Sertoli cells precedes rearrangement of the centrioles and Golgi and is not te mporally related to the formation of the tight junctional complex of t he blood testis barrier.