Pattern of X-Y Chromosome Pairing in Microtine Rodents

Sex chromosome evolution in mammals has been extensively investigated through chromosome-painting analyses. In some rodent species from the subfamily Arvicolinae the sex chromosomes contain remarkable features such as giant size, a consequence of heterochromatic enlargement, or asynaptic behaviour during male meiosis. Here, we have made a comparative study of the sex chromosomes in 6 arvicolid species using different probes from the X and Y chromosomes of 3 species, in order to gain knowledge about intra- or interspecific preservation of euchromatic regions. Our results clearly reveal poor conservation of the euchromatic region of the Y chromosome within these species, while the euchromatin on the X chromosome is extremely well preserved. Furthermore, we detected no clear correlation between the synaptic/asynaptic behaviour of the sex chromosomes, and the presence or absence of sequence homology within their euchromatic regions. Notably, our study has shown a new relationship between the giant sex chromosomes of 2 species, Microtus agrestis and Microtus cabrerae, that is, both X and Y share a novel region of common sequences in the euchromatin that is not present in the other species analysed. This interspecific euchromatic conservation, limited to the giant sex chromosomes, could point towards a common evolutionary origin for the heterochromatic enlargement process that has characterized the evolution of the sex chromosomes in some arvicolid species.

Section: Sex Chromosome Pairing and Pseudoautosomal Regions (Pars)mentioning

confidence: 74%

mentioning

confidence: 99%

Comparative Analysis by Chromosome Painting of the Sex Chromosomes in Arvicolid Rodents

Acosta

Romero-Fernández²,

Sánchez³

et al. 2010

“…One of them stated that large heterochromatic regions on sex chromosomes could interfere with synapsis (Solari and Ashley, 1977). However, asynapsis also occurs in species without heterochromatic regions on sex chromosomes (Ashley et al, 1989;Carnero et al, 1991;Borodin et al, 1995;Megías-Nogales et al, 2003). Also, the loss or malfunction of the pairing regions in sex chromosomes has been proposed as the cause of asynapsis Jiménez et al, 1991).…”

Section: Synaptic and Asynaptic Sex Chromosomesmentioning

confidence: 99%

Sex chromosomes, sex determination, and sex-linked sequences in Microtidae

Marchal

Acosta

Bullejos

et al. 2003

The Arvicolidae is a widely distributed rodent group with several interesting characteristics in their sex chromosomes. Here, we summarize the actual knowledge of some of these characteristics. This mammalian group has species with abnormal sex determination systems. In fact, some species present the same karyotype in both males and females, with total absence of a Y chromosome, and hence of SRY and ZFY genes. Other species present fertile, sex-reversed XY females, generally due to mutations affecting X chromosomes. Furthermore, in Microtus oregoni males and females are gonosomic mosaic (the females are XO in the soma and XX in the germ cells, while the males are XY in the soma and OY in the germ cells). Regarding sex chromosomes, some species present enlarged (giant) sex chromosomes because of the presence of large blocks of constitutive heterochromatin, which have been demonstrated to be highly heterogeneous. Furthermore, we also consider the alterations affecting composition and localization of sex-linked genes or repeated sequences. Finally, this rodent group includes species with synaptic and asynaptic sex chromosomes. In fact, several species with asynaptic sex chromosomes have been described. It is interesting to note that within the genus Microtus both types of sex chromosomes are present.

“…In species of the "arvalis" group, the X does not pair with the Y. Lacking a pairing partner, the X often pairs with itself and thereby produces crisscross and foldback configurations (Borodin et al, 1995). The presence of large clusters of repeated or duplicated sequences in the vole X chromosomes would facilitate self-pairing and recombination between X chromosome regions that would result in deletion, duplication or inversion.…”

Section: Discussionmentioning

confidence: 99%

Reorganization of the X chromosome in voles of the genus <i>Microtus</i>

Rubtsov

Rubtsova²,

Anopriyenko³

et al. 2002

Comparative chromosomal analysis is a powerful tool in the investigation of the mechanisms of chromosomal evolution. The accuracy of the analysis depends on the availability of region-specific markers to follow the fate of the particular chromosomal region through the evolution of species. We have assigned 12 unique sequences to the euchromatic part of the vole X chromosome, which serve as reliable markers of chromosomal segments. Together with region-specific libraries and GTG banding, these markers allow us to delineate the homologous regions of the X chromosomes in five species of the genus Microtus. We found that X chromosomes of these species differ by numerous rearrangements and all rearrangements are clustered at specific breakpoints. Moreover, these breakpoints were found to colocalise with repetitive and/or duplicated DNA sequences. We suggest that clusters of repeated and/or duplicated DNA sequences have played a crucial role in the formation of rearrangement hot spots during evolution of the X chromosome in the subgenus Microtus.