Sparse distribution of constitutive heterochromatin and its variation in two species of mongooses (Carnivora) with exact G-band homology

The cryptic Y-autosome translocation in the small Indian mongoose, Herpestes auropunctatus, revealed by molecular cytogenetic approaches

In initial studies of the eutherian small Indian mongoose (Herpestes auropunctatus), the Y chromosome could not be identified in somatic cells. The male chromosome number is uniquely odd, 2n = 35, whereas that of females is 2n = 36. Previous reports indicated that this unique karyotype resulted from a translocation of the ancestral Y chromosome to an autosome. However, it has been difficult to identify the chromosomes that harbor the translocated Y chromosomal segment because it is an extremely small euchromatic region. Using a Southern blot analysis, we detected four conserved Y-linked genes, SRY, EIF2S3Y, KDM5D, and ZFY, in the male genome. We cloned homologues of these genes and determined their sequences, which showed high homology to genes in two carnivore species, cat and dog. To unambiguously identify the Y-bearing autosome, we performed immunostaining of pachytene spermatocytes using antibodies against SYCP3, γH2AX, and the centromere. We observed trivalent chromosomes, and the associations between the distal ends of the chromosomes were consistent with those of Y and X1 chromosomes. The centromere of the Y chromosome was located on the ancestral Y chromosomal segment. We mapped the complementary DNA (cDNA) clones of these genes to the male chromosomes using fluorescence in situ hybridization (FISH), and the linear localization of all genes was confirmed by two-colored FISH. These Y-linked genes were localized to the proximal region of the long arm of a single telomeric chromosome, and we successfully identified the chromosome harboring the ancestral Y chromosomal segment.

Identification and patterns of synapsis of the autosomally translocated Y-chromosome of the Indian mongoose, Herpestes auropunctatus (Hodgson)

The multiple sex chromosome system, X1X2Y male/X1X1X2X2 female, in the small Indian mongoose, Herpestes auropunctatus, results from a translocation of a part of Y chromosome to an autosome. It is not possible to distinguish the autosome which harbours the Y chromosome element in the somatic complement. By employing the surface-spreading technique to prophase I meiocytes we have identified the region to which the Y chromosome has been translocated as the short arm of chromosome 9 which is a subtelocentric chromosome. This Y chromosome component lacks heterochromatin and no sex vesicle is organised during meiotic prophase. This suggests to us that Y heterochromatin in mammals may be required for the production of a sex vesicle.