The SMC5/6 complex is involved in crucial processes during human spermatogenesis.

Genome integrity is crucial for safe reproduction. Therefore, chromatin structure and dynamics should be tightly regulated during germ cell development. Chromatin structure and function are in large part determined by the structural maintenance of chromosomes (SMC) protein complexes, of which SMC5/6 recently has been shown to be involved in both spermatogonial differentiation and meiosis during mouse spermatogenesis. We therefore investigated the role of this complex in human spermatogenesis. We found SMC6 to be expressed in the human testis and present in a subset of type Adark and type Apale spermatogonia, all spermatocytes, and round spermatids. During human meiosis, SMC5/6 is located at the synaptonemal complex (SC), the XY body, and at the centromeres during meiotic metaphases. However, in contrast to mouse spermatogenesis, SMC6 is not located at pericentromeric heterochromatin in human spermatogenic cells, indicating subtle but perhaps important differences in not only SMC5/6 function but maybe also in maintenance of genomic integrity at the repetitive pericentromeric regions. Nonetheless, our data clearly indicate that the SMC5/6 complex, as shown in mice, is involved in numerous crucial processes during human spermatogenesis, such as in spermatogonial development, on the SC between synapsed chromosomes, and in DNA double-strand break repair on unsynapsed chromosomes during pachynema.