Anatomy and chromosomes of two intersexual dasyurid marsupials

Abstract

The intersexual phenotypes of marsupials with XXY and XO chromosome constitutions imply that not all sexual dimorphisms are under the control of testicular hormones and, ultimately, the SRY gene on the Y chromosome. It has been hypothesised that there is a gene on the X chromosome that determines whether either a scrotum will form (one copy of the gene) or a pouch with teats (two copies of the gene). Here, we describe the anatomy and chromosomes of two intersexual dasyurid marsupials. One, a Dasyuroides byrnei, had a pouch, but the reproductive tract was essentially male. The other, a Sminthopsis douglasi, had a hemipouch and a hemiscrotum and the reproductive tract was essentially female. The S. douglasi was a mosaic for cells with an apparently normal 2n = 14, XX female karyotype and cells with 2n = 14 plus (usually) two dot-like supernumerary elements 2n = 14, XX + 2B. The D. byrnei cells examined also had a 2n = 14, XX + 2B karyotype. In fibroblasts from the male and female sides of the S. douglasi, it was possible to assign the 2n = 14, XX karyotype to the male side and the 2n = 14, XX + 2B to the female side.

Isolation of chromosomal regions controlling intersex development in a marsupial

“…Its external features were described previously (Woolley and Graves, 2003). Fibroblast cell lines from skin derived from both sides of the intersex animal, as well as from normal male and female siblings, were available from this animal.…”

“…We reported that cells from the male side had an apparently normal female karyotype (2n = 14, XX) and cells from the female side had a female karyotype plus two extra elements (2n = 14, XX + 2B). Another dasyurid animal (Dasyuroides byrnei) with a similar phenotype, was discovered in 1967 (Woolley et al, 2003). Lymphocytes contained two cell populations, one with an apparently normal female karyotype, and the other with a female 2n = 14, XX karyotype, plus two dot-like chromosomes.…”

“…An intersex dasyurid marsupial (Sminthopsis douglasi) was found recently (Woolley et al, 2003) having a hemi-pouch and teats on the left and a hemi-scrotum on the right side. The reproductive tract was essentially female, with well differentiated ovaries and no sign of testes.…”

“…In the paper by Woolley et al (2003), one of us (JAMG) put forward the hypothesis that the dot-like elements represent material (including PMS) deleted from the X at an early stage of embryogenesis, and segregated unequally so that one daughter cell received two, and the other none. These cells gave rise to lineages with different genotypes on the left and right of the animal (Fig.…”