Male mice homozygous for the tw2 haplotype are sterile. Although many of the seminiferous tubules degenerate and are devoid of germ cells, as seen in the tw8 haplotype, other seminiferous tubules have an abnormal phenotype that is distinct from that in tw8/tw8 testes (Fig. 1). Previous studies with tw2/tw2 testes have shown that the nuclear envelope becomes discontinuous in a small proportion of elongating spermatids, allowing direct contact between the cytoplasm and nucleoplasm. These cells lack manchet-tes: either they never formed, or they underwent premature depolymerization. The majority of elongating spermatids contain large numbers of disorganized microtubules and the cells have abnormal head shapes. Abnormal spermatids, as in the tw8 haplotype, are phagocytized by the Sertoli cells prior to spermiation. buy ortho tri-cyclen online
Light microscopy studies examining SPNR staining in tw2/tw2 testes showed the same abnormal proliferation of microtubules that was found in electron micrograph studies (arrow, tw2 panel, Fig. 1). Sertoli cell phagocytosis of SPNR-staining cells was also evident (arrowhead, tw2 panel, Fig. 1). SPNR was found abundantly in rounded cells that were reminiscent of the degenerating spermatids found in hop/hop seminiferous tubules (Fig. 1). Confocal micrographs showed that SPNR and tubulin colocalized on highly abnormal manchette structures, structures that even extended into the lumen of seminiferous tubules, entirely free of a nuclear association (arrows, Fig. 4, I and L). Thus, as in hop testes, spermatogenesis in the tw2 haplotype is characterized by an overproliferation of abnormal microtubules that is followed by premature depolymerization and cell degeneration.