<i>Ellobius lutescens</i>: Sex Determination and Sex Chromosome

Abstract

The mole vole Ellobius lutescens is an interesting animal, not only concerning its sex determination mechanism without the Y-chromosomal Sry gene, that triggers sex determination in nearly all other mammalian species, but also regarding the karyotype with an odd number of chromosomes, being identical in male and female animals. The odd chromosome represents the X chromosome, and therefore, even males do not have a Y chromosome. We present an overview of a search for candidate genes of male sex determination in the mole vole Ellobius lutescens. A singular X raises questions about the need for X chromosome inactivation in female cells. We present preliminary data that support a hypothesis that the E. lutescensXist gene may be degenerated and thus non-functional.

Did sex chromosome turnover promote divergence of the major mammal groups?

“…Interestingly, the X chromosome in both these groups of Y‐less rodents has not reverted to an autosomal state 77, perhaps because X‐borne genes are upregulated so that two copies are deleterious.…”

Chromatin structural changes around satellite repeats on the female sex chromosome in Schistosoma mansoni and their possible role in sex chromosome emergence

“…The suppression of recombination between the heterochromosome and its homologue would trigger gradual degradation of the heterochromosome (Y in XY systems, or W in WZ systems) because genes that are not essential for males (in XY systems) or females (in WZ systems) show accelerated rates of mutation and deletion. Consequently, the heterochromosome becomes progressively gene-poor (for example, [11]) and in the extreme case the degradation process can lead to the complete loss of the heterochromosome (for example, [12]).…”

Sexual dimorphism in prophase I of meiosis in the Northern mole vole (Ellobius talpinus Pallas, 1770) with isomorphic (XX) chromosomes in males and females

“…There are at least four types of deviations (Veyrunes et al, 2010): (1) typical XY males and different females with XX and XY in Myopus schisticolor Lilljeborg, 1844, Dicrostonyx torquatus Pallas, 1778, Akodon sp. (Fredga, 1983(Fredga, , 1994Hoekstra, Edwards 2000;Ortiz et al, 2009); (2) typical XY males and deviant XO females (single X) in Microtus oregoni Bachman, 1839 (Ohno et al, 1966;Fredga, 1983); (3) females and males with XO karyotypes in Tokudaia osimensis Abe, 1933, T. tokunoshimensis Endo et Tsuchiya, 2006(Arakawa et al, 2002 and Ellobius lutescens Thomas, 1897 (Matthey 1953;Just et al, 1995); (4) males and females with identical isomorphic XX in three sibling species of Ellobius, E. tancrei Blasius, 1884, E. talpinus Pallas, 1770 and E. alaicus Vorontsov et al, 1969(Vorontsov et al, 1980Bakloushinskaya, Lyapunova, 1990;Just et al, 2007;Romanenko et al, 2007).…”