Heterochromatin variation and spermatogenesis in Nesokia.

A probable role of heterochromatin variation in male meiosis has been evaluated using fertile and infertile Indian mole rat males (Nesokia) with polymorphic X and/or Y chromosomes. A comprehensive study of tubular histology, meiotic progression, and X-Y chromosome pairing was undertaken. Despite heterochromatin variation, spermatogenesis was found to be complete in all individuals. Patterns of X-Y synaptonemal complex pairing varied considerably from extensive synapsis in individuals with a normal heterochromatin complement, through end-to-end synapsis, to X and Y univalents in those with different degrees of loss of heterochromatin. Changes in the gonadal histology corresponding to heterochromatin variation were also observed. Loss of some coding DNA sequences in polymorphic X-chromosomes otherwise located at specific sites in the X-chromosome heterochromatin have been linked directly to modifications of the reproductive process. This is thought to be mediated by an altered X-chromosome activity during spermatogenesis or regulation of other locus/loci involved in fertility or reproduction.