Basigin is a highly glycosylated transmembrane protein with two immunoglobulin-like domains. We generated mutant mice lacking the basigin gene (Bsg) by gene targeting. Bsg (-/-) embryos developed normally during preimplantation stages. However, the majority of Bsg (-/-) embryos died around the time of implantation. At this time, basigin mRNA was strongly expressed in the trophectoderm, embryo proper, and uterine endometrium of Bsg (+/+) mice. These results suggest that basigin is involved in intercellular recognition during implantation. Embryos which survived the critical period yielded Bsg (-/-) mutant mice. Half of the mutant mice died before 1 month after birth, due to interstitial pneumonia. The surviving adult mutant mice were small and sterile. Spermatogenesis was arrested in the mutant mice. Most of the spermatocytes in the Bsg (-/-) mouse were arrested and degenerated at the metaphase of the first meiosis, and only a small number differentiated to step 1 spermatids. In the female mutants, the ovaries and genital tract were morphologically normal, and the defect was probably in the capability of implantation of the uterus. In conclusion, basigin is an important cell-surface molecule involved in early embryogenesis and reproduction.

The distribution of intermediate filament (IF) subunits during maturation of skeletal myotubes in vitro was examined by immunofluorescence, using antibodies against two different types of chick IF subunits: (a) 58-kdalton subunits of fibroblasts (anti-58K), and (b) 55-kdalton subunits of smooth muscle (anti-55K) . Anti-58K bound to a filament network in replicating presumptive myoblasts and fibroblasts, as well as in immature myotubes. The distribution in immature myotubes was in longitudinal filaments throughout the cytoplasm . With maturation, staining of myotubes by anti-58K diminished and eventually disappeared . Anti-55K selectively stained myotubes, and the fluorescence localization underwent a drastic change in distribution with maturation-from dense, longitudinal filaments in immature myotubes to a cross-striated distribution in mature myotubes that was associated with the I-Z region of myofibrils . However, the emergence of a cross-striated anti-55K pattern did not coincide temporally with the emergence of striated myofibrils, but occurred over a period of days thereafter. KEY WORDS intermediate filaments myogenesis " muscle differentiation immunofluorescenceReports from this laboratory and from others have demonstrated that the intermediate or 100-A filament (IF) subunits from different cell types and organisms are not all identical, and can be distinguished immunologically and biochemically (I,2,9, 11a, IIb,21,29) . We demonstrated that antibodies against the 58-kdalton chick fibroblast IF subunit (anti-58K) stained filaments in many different kinds of cultured chick cells, including fibroblasts, chondroblasts, melanocytes, neurons, glia, cardiac and smooth muscle myoblasts, and both replicating presumptive skeletal myoblasts and postmitotic myoblasts and myotubes. Contrastingly, antibodies against the 55-kdalton chick smooth muscle IF subunit (anti-55K) were highly selective and stained only definitive smooth, cardiac, and skeletal muscle cells. Replicating pre-J . CELL BIOLOGY

We cloned a testis-specific cDNA from mice that encodes a histone H1-like, haploid germ cell-specific nuclear protein designated HANP1/H1T2. The HANP1/H1T2 protein was specifically localized to the nuclei of murine spermatids during differentiation steps 5 to 13 but not to the nuclei of mature sperm. HANP1/H1T2 contains an arginine-serine-rich domain and an ATP/GTP binding site, and it binds to DNA, ATP, and protamine. To investigate the physiological role of HANP1/H1T2, we generated Hanp1/H1T2-disrupted mutant mice. Homozygous Hanp1/H1T2 mutant males were infertile, but females were fertile. Although a substantial number of sperm were recovered from the epididymides, their shape and function were abnormal. During sperm morphogenesis, the formation of nuclei was disturbed and protamine-1 and -2 were only weakly detectable in the nuclei. The chromatin packaging was aberrant, as demonstrated by electron microscopy and biochemical analysis. The mutant sperm exhibited deficient motility and were not competent to fertilize eggs under in vitro fertilization conditions; however, they were capable of fertilizing eggs via intracytoplasmic sperm injection that resulted in the birth of healthy progeny. Thus, we found that HANP1/H1T2 is essential for nuclear formation in functional spermatozoa and is specifically involved in the replacement of histones with protamines during spermiogenesis. At the time of submission of the manuscript, we found an independent publication by The complex process of spermatogenesis includes three major events: proliferation and differentiation of the spermatogonia, meiotic prophase in the spermatocytes, and drastic morphological changes during differentiation from the haploid round spermatids to the mature sperm (24). These events begin after birth, and approximately 35 days are required for the development of mature sperm in the mouse. The differentiation of the haploid germ cells (spermiogenesis) begins at 17 days of age in the mouse. Spermiogenesis involves diverse and complex processes, such as packaging and remodeling of the haploid germ cell nucleus, rearrangement of mitochondria, development of the flagellum, and formation of the acrosome. During this phase, the composition of the chromatin is altered dramatically (29). The changes in the nuclear proteins occur in association with the displacement of general nucleohistones by transition proteins (TNP) and other proteins, including a number of testis-specific histones and nonhistone chromosomal proteins (3,12,13,17,31) that are subsequently replaced with protamines to form nucleoprotamines (2, 20). The transition from histones to protamines in the chromatin of the haploid germ cells is accompanied by epigenetic changes (19) and the specific formation of nuclei in the sperm (25); these changes are associated with chromosome condensation and the shaping of the nucleus. Recently, mice with null mutations in TNP1 or TNP2 were found to be subfertile (32, 33), and mice with null mutations in both TNP1 and TNP2 were infertile (34). The nuclei of...

The haploid germ cell-specific Tektin-t protein is a member of the Tektin family of proteins that form filaments in flagellar, ciliary, and axonemal microtubules. To investigate the physiological role of Tektin-t, we generated mice with a mutation in the tektin-t gene. The homozygous mutant males were infertile, while the females were fully fertile. Sperm morphology and function were abnormal, with frequent bending of the sperm flagella and marked defects in motility. In vitro fertilization assays showed that the defective spermatozoa were able to fertilize eggs. Electron microscopic examination showed that the dynein inner arm structure was disrupted in the sperm flagella of tektin-t-deficient mice. Furthermore, homozygous mutant mice had functionally defective tracheal cilia, as evidenced by altered dynein arm morphology. These results indicate that Tektin-t participates in dynein inner arm formation or attachment and that the loss of Tektin-t results in impaired motility of both flagella and cilia. Therefore, the tektin-t gene is one of the causal genes for immotilecilium syndrome/primary ciliary dyskinesia.

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