Random/nonrandom X-chromosome inactivation in <i>Nesokia indica: </i>possible influence of heterochromatin

Abstract

Five types of X chromosomes with different amounts of heterochromatin have been observed in Nesokia indica, the Indian mole rat. They have been found in both mosaic and non-mosaic individuals. The influence, if any, of heterochromatin on the kinetics of X-chromosome DNA replication was evaluated in bone marrow cells and peripheral blood lymphocytes of Nesokia females with variant X chromosomes. In bone marrow cells of nonmosaic females a random X-chromosome inactivation (XCI) pattern was observed, except when there was a total loss of heterochromatin from the variant X chromosome, resulting in predominantly early replication. A nonrandom pattern was observed, however, in blood and bone marrow cells of all individuals with mosaic genotypes. In these females the X chromosome with the lesser amount of heterochromatin was predominantly the active one. The amount of heterochromatin per se or, more likely, specific sequences contained in the heterochromatic region seem to influence the XCI pattern in a cis-acting manner. The observations also seem to support a process of cell selection in individuals with variant X chromosomes.

Polymorphic karyotypes and sex chromosomes in the tufted deer <i>(Elaphodus cephalophus)</i>: cytogenetic studies and analyses of sex chromosome-linked genes

“…Five different types of X chromosomes have been observed in Nesokia indica, the predominant type being a large metacentric (16 % of the total chromosome length), consisting of a short euchromatic arm and a long heterochromatic arm. In this species by deletion of different amounts of heterochromatin at specific sites and random/ nonrandom X chromosome inactivation, body size, weight, and the events which ultimately result in reproductive inability or reduced fertility of individuals are influenced (Juyal et al, 1989;Thelma et al, 1991). Polymorphic sex chromosomes were also observed in the South American rice rats of the genus Oryzomys (Volobouev and Aniskin, 2000) and in the species of Arvicanthis (Garagna et al, 1999).…”