Identification and redistribution of lamins during nuclear differentiation in mouse spermatogenesis

Chromatin may be attached to the nuclear envelope through interaction of the nuclear membrane lamins A, B, and C. Such a hypothesis requires that these proteins are present in all cells with chromatin attachment to the nuclear envelope. We have investigated the distribution of the lamins during spermatogenesis in mouse, which exhibits extremes in nuclear envelope structural changes. By immunohistochemical techniques using human auto-antibodies and monoclonal antibodies against these molecules, we found that the lamins persist through all stages of spermatogenesis, though in highly variable amounts. They are also present during meiotic prophase (pachytene) when chromosomes are only locally attached to the nuclear envelope, analogous to the early prophase of somatic cells. Restructuring of the early spermatid nuclear envelope is accompanied by the appearance of a new lamin at the acrosomal fossa. In the epididymal spermatozoon the distribution of different lamins varies markedly over the nucleus suggesting special structural functions. The presence of lamins throughout spermatogenesis supports the concept that they are a general feature of the nuclear envelope structure, even where a lamina is not recognizable ultrastructurally.