Architecture of the nuclear periphery of rat pachytene spermatocytes: Distribution of nuclear envelope proteins in relation to synaptonemal complex attachment sites

The nucleus of spermatocytes provides during the first meiotic prophase an interesting model for investigating relationships of the nuclear envelope ( NE) with components of the nuclear interior. During the pachytene stage, me iotic chromosomes are synapsed via synaptonemal complexes (SCs) and attache d through both ends to the nuclear periphery. This association is dynamic b ecause chromosomes move during the process of synapsis and desynapsis that takes place during meiotic prophase. The NE of spermatocytes possesses some peculiarities (e.g., lower stability than in somatic cells, expression of short meiosis-specific lamin isoforms called C2 and B3) that could be criti cally involved in this process. For better understanding of the association of chromosomes with the nuclear periphery, in the present study we have in vestigated the distribution of NE proteins in relation to SC attachment sit es. A major outcome was the finding that lamin C2 is distributed in the for m of discontinuous domains at the NE of spermatocytes and that SC attachmen t sites are embedded in these domains. Lamin C2 appears to form part of lar ger structures as suggested by cell fractionation experiments. According to these results, we propose that the C2-containing domains represent local r einforcements of the NE that are involved in the proper attachment of SCs.