ACTIN-RELATED INTERCELLULAR-JUNCTIONS IN THE GERMINAL COMPARTMENT OF THE TESTIS IN POECILIA-RETICULATA (TELEOSTEI, POECILIIDAE)

In this paper we present evidence for the presence of actin-related ju nctions between neighboring Sertoli cells and between Sertoli cells an d spermatids in the testis of the guppy (Poecilia reticulata). In the guppy, spermatogenesis occurs in spermatocysts that are lined by a sim ple squamous to cuboidal epithelium formed of Sertoli cells. At a cert ain stage of differentiation, elongate spermatids occur in Sertoli cel l recesses in the apical surface of Sertoli cells. When evaluated by e lectron microscopy, junctions occur between Sertoli cells and spermati ds situated in the recesses. In these regions, obvious linkages occur between the plasma membrane of Sertoli cell recesses and the adjacent spermatids. Moreover, large concentrations of microfilaments occur in the Sertoli cell cytoplasm immediately underlying the crypts. Also, ju nctional complexes are apparent between neighboring Sertoli cells near the apical surface of the epithelium. These complexes consist of micr ofilament-related components (probably contributing to both tight and adhesion junctions), which occur closest to the lumen, and intermediat e-filament related desmosomes, which occur more basally. In fixed froz en sections of guppy testis, probes for filamentous actin (rhodamine p halloidin) and myosin II (polyclonal antisera raised against human pla telet myosin II) react with junction regions between neighboring Serto li cells and between Sertoli cells and spermatids. We conclude that ac tin-related junctions occur at both these sites and that the actin net works have contractile properties because they contain myosin II.