Conserved although Very Different Karyotypes in Gliridae and Sciuridae and Their Contribution to Chromosomal Signatures in Glires

Abstract

Rodents represent the largest order of living mammals. It comprises 5 sub-orders, among which Sciuromorpha (Sciuridae, Gliridae and Aplodontiidae) are assumed to occupy a basal position in rodent evolution. Banded karyotypes of some representatives of the Sciuridae family have been compared to each other, and comparisons with man were performed using chromosome paintings. Sciuridae karyotypes have conserved several eutherian ancestral syntenies. Like Sciuridae, Gliridae possess some chromosomes easily comparable with those of Primates. Comparisons of Gliridae and Sciuridae chromosomes with those of the presumed eutherian ancestor provide information about their chromosomal evolution and their position among Rodentia. Although both Sciuridae and Gliridae karyotypes are relatively conserved, they display many differences, indicating their early divergence. The reconstruction of their chromosomal evolution allowed us to propose the composition of their presumed ancestral karyotypes, with 2n = 48 and 2n = 38 for Gliridae and Sciuridae, respectively. Since rodent emergence, a single rearrangement is common to these 2 families. It formed a chromosome with fragments homologous to human chromosomes 4-8p-4-12-22, not detected in other rodents, and thus characteristic for the Sciuromorpha. This allowed us to reassess the chromosomal signatures of Rodentia. Finally, we show that the speed of chromosomal evolution in Gliridae is intermediate between that of Sciuridae (low) and Muridae (high).

Chromosomal evolution in Rodentia

“…However, the most recent glirid painting data showed the absence of HSA 9/11 and 3/19 in Eliomys. In the light of these findings, we concur with Sannier et al (2011) that the occurrence HSA 9/11 cannot be unequivocally explained. It could be a result of convergence in some lagomorphs, sciurids and myomorphs, or it may represent an ancestral feature that was lost in certain branches.…”

“…The karyotypes of Gliridae are also relatively conserved. Comparison of three Eliomys species made by fluorescence in situ hybridization (FISH) using human probes and RBG-banding (R-bands by BrdU using Giemsa) revealed the retention of several eutherian ancestral syntenies in their genomes (Sannier et al, 2011). As karyotypes of other glirids have not yet been studied, and because the different Eliomys karyotypes are conserved, one might consider the E. melanurus syntenies to reflect the chromosomal signatures for glirids in general.…”

“…Thus, only five fusions are needed to explain the derivation of the Sciuridae Ancestral Karyotype from that of the putative ancestral Sciuromorpha karyotype. Many more rearrangements (12 fissions and 12 fusions) are needed to form a putative ancestral Rodentia karyotype from that of the ancestral Gliridae (Sannier et al, 2011).…”

Low, Complex and Probably Reticulated Chromosome Evolution of Sciuromorpha (Rodentia) and Lagomorpha

“…In contrast, Gliridae have a diploid number varying from 46 (E. munbyanus) to 62 (Glis glis) . There are different cytotypes for some Eliomys species ( table 1 ) with a diploid number varying from 48 to 54 (E. quercinus) or 46-48 (E. melanurus) , following Robertsonian fusion or fission events [Zima et al, 1995;Sannier et al, 2011].…”

“…This number is informative about the speed of chromo- Chromosomes are classified according to Callosciurus sp . karyotype in Sannier et al [2011], and heterochromatic arms were not taken into consideration for chromosome orientation. h = Heterochromatin.…”