Evolutionary conservation of a germ cell-specific lamin persisting through mammalian spermiogenesis

We had identified earlier a germ cell-specific lamin of 60 kDa in rat which is related to somatic lamin B. This polypeptide was shown to be the only major component organizing the lamina structure of round spermatids. In the present study, we find that this 60-kDa polypeptide persists in the testicular and epididymal sperms of rat. We also show, by indirect immunofluorescence studies, that the 60-kDa protein is antigenically conserved in the germ cells of grasshopper, rooster, and frog and in plant meiocytes. The distribution of fluorescence among the various germ cell populations shows that the antigen is located around the nuclear cortex of pre- and postmeiotic germ cells, while it is distributed all over the pachytene nuclei. The anti-60-kDa polyclonal antibodies also reacted with a 60-kDa polypeptide in the Western blot analysis of nuclear matrix proteins of grasshopper germ cells. The similar fluorescent localization pattern of the antigen observed in various eukaryotic species strongly suggests that this germ cell-specific lamin may play a very crucial role during meiotic prophase, particularly during homologous chromosome pairing and recombination.