Rates of sex chromosome loss during development in differen tissues of the bandicoots perameles nasuta and isoodon macrourus (marsupialia: Peramelidae)

Abstract

An X chromosome disappears from female cells and the Y chromosome from male cells of some somatic tissues of all peramelid bandicoots, leaving cells with a 2n = 13 (i.e. XO) chromosome complement. The patterns of loss, which differ among tissues and species, were studied during development of specimens of P. nasuta and I. macrourus. In the lung, kidney and heart of both species, most cells retained both sex chromosomes for as late in development as mitoses could be found; yet therewas much individual variation among littermates in the percentage of XO cells present. No differences in chromosome counts between species or sexes were apparent. Cells from intestinal epithelium ofI. macrourus had begun to lose a sex chromosome before 19 days of pouch life whereas corneal epithelium of female I. macrourus remained 2n = 14 (XX) until the animals were more than 12 months old. By contrast, all corneal cells in male I. macrourus aged more than 6 months were 2n = 13 (XO). Cultured fibroblasts of I. macrourus remained 2n = 14 after 4 weeks of culture. All the results obtainedin this study and those reported in studies of petaurid species can be explained ifsex chromosome loss in marsupials is an incidental by-preduct of dosage compensation. The mitotic error underlying sex chromosome loss could then be triggered or influenced by one or a combination of several characteristics such as mitotic rate, state of differentiation, or the age of the cell line. Every cell line in each tissue, species and sex is likely to have different set of such characteristics which would then lead to different patterns of sex chromosome loss. © 1984 ASEG.