CHANGE OF KARYOSKELETON DURING MAMMALIAN SPERMATOGENESIS - EXPRESSIONPATTERN OF NUCLEAR LAMIN C2 AND ITS REGULATION

Nuclear lamins are a multigene family of major karyoskeletal proteins. The expression pattern of members of the lamin family has been shown to be developmentally regulated. Of particular interest have been the findings that mammalian spermatogenic cells express two small lamin is oforms (B3 and C2) which are shorter splicing variants of their somati c counterparts (the lamins B2 and C, respectively). Although lamins B3 and C2 appear to be specific for the germ line, the expression patter n and localization of these proteins is not known. In the present stud y, we present evidence that during rat spermatogenesis lamin C2 is sel ectively expressed in spermatocytes, i.e., the cells undergoing meiosi s. As in the case of other members of the family, lamin C2 was detecte d at the nuclear periphery. Northern blotting and in situ hybridizatio n indicate that meiotic expression of lamin C2 is regulated at the tra nscriptional level. This is in contrast to the situation during amphib ian oogenesis, where lamin expression is largely posttranscriptionally regulated. Interestingly, the expression pattern of lamin Ca temporal ly coincides with that of structural protein components of another mei osis-specific karyoskeletal structure, the synaptonemal complex (SC). Taken together, we conclude that pairing and recombination of homologo us chromosomes during meiotic prophase is accompanied by significant c hanges in the organization of the karyoskeleton which are accomplished by the expression of stage-specific proteins. (C) 1996 Academic Press , Inc.