Complete Mitochondrial Genome of Three Species of the Genus Microtus (Arvicolinae, Rodentia).

The 65 species of the genus Microtus have unusual sex-related genetic features and a high rate of karyotype variation. However, only nine complete mitogenomes for these species are currently available. We describe the complete mitogenome sequences of three Microtus, which vary in length from 16,295 bp to 16,331 bp, contain 13 protein-coding genes (PCGs), two ribosomal RNA genes, 22 transfer RNA genes and a control region. The length of the 13 PCGs and the coded proteins is the same in all three species, and the start and stop codons are conserved. The non-coding regions include the L-strand origin of replication, with the same sequence of 35 bp, and the control region, which varies between 896 bp and 930 bp in length. The control region includes three domains (Domains I, II and III) with extended termination-associated sequences (ETAS-1 and ETAS-2) in Domain I. Domain II and Domain III include five (CSB-B, C, D, E and F) and three (CSB-1, CSB-2, and CSB-3) conserved sequence blocks, respectively. Phylogenetic reconstructions using the mitochondrial genomes of all the available Microtus species and one representative species from another genus of the Arvicolinae subfamily reproduced the established phylogenetic relationships for all the Arvicolinae genera that were analyzed.

Karyotype Analysis of the New Talpa Species Talpa aquitania (Talpidae; Insectivora) from Northern Spain.

Karyotypes of 3 male Talpa specimens from northern Spain were analyzed. The mesostyles of upper molars and cytochrome b sequence analysis identified these specimens as belonging to Talpa aquitania, a new Talpa species recently described from northern Spain and southern France. We describe here for the first time the karyotype of Talpa aquitania. Its diploid number is 2n = 34 and NFa = 64, and all chromosomes including the sex chromosomes are biarmed, either metacentric or submetacentric. G-banding demonstrated that the karyotypes of T. aquitania and T. occidentalis (the most closely related species) are almost identical. However, the karyotype of T. aquitania differs from the karyotypes of both T. europaea and T. occidentalis in that it has a medium-sized biarmed Y chromosome rather than a dot-like chromosome and that chromosome 16 is submetacentric in T. aquitania but has a small p-arm in both T. europaea and T. occidentalis. Pericentromeric C-bands were scarce and only clearly visible in a few chromosomal pairs. In addition, C-banding demonstrated that half of the 14p, the 16p, and the Y chromosome are all heterochromatic. rDNA genes were located at the secondary constriction in autosomal pair 3, a common feature in the karyotypes of all Talpa species. Hybridization signals for telomeric repeats were found on the telomeres and the pericentric regions of some chromosomes and co-localized in the secondary constriction of pair 3 with the rDNA genes. In conclusion, the karyotype of T. aquitania from northern Spain is very similar to the karyotype of other species belonging to the genus Talpa.

Complete mitochondrial genome of the Iberian Mole Talpa occidentalis (Talpidae, Insectivora) and comparison with Talpa europaea.

The complete mitogenome of Talpa occidentalis, the Iberian mole, was sequenced using a combination of the Illumina and Sanger methods. The 16,962 bp genome obtained contains 13 protein-coding genes, 22 transfer RNAs, 2 ribosomal RNAs, and a control region. Thirty-seven identical repetitions of a 10-nucleotide (CACACGTACG) repeat element were identified in the non-coding control region (D-loop). The number, order, and orientation of the mitochondrial genes are the same as in T. europaea, the only mitogenome published so far for this genus. These two mitogenomes differ only at the repeat element included in the control region. The phylogeny obtained for the Talpidae species using the protein-coding genes of these mitogenomes agrees with the current classification of this family.

Structural and Evolutionary Relationships in the Giant Sex Chromosomes of Three Microtus Species.

The genus Microtus has high karyotypic diversity. The existence of notable differences in the length of its sex chromosomes contributes to this variation. Variations in size are attributed to the enlargement of their heterochromatin content, which is of such magnitude in some species that they are referred to as "giant sex chromosomes". Here, we perform an intra- and interspecific analysis of the molecular composition of the heterochromatic blocks in three species with giant sex chromosomes (Microtus chrotorrhinus, M. cabrerae and M. agrestis). Our results show that the heterochromatic content is very similar in both the X and Y chromosomes of M. chrotorrhinus, and that their molecular composition is more closely related to the heterochromatic blocks of M. agrestis than to the sex heterochromatin of M. cabrerae; however, species-specific differences do clearly exist. Interestingly, the euchromatic regions of the X chromosome of all three of these species share a homologous region composed of heterochromatic-related sequences. Our results therefore reinforce the idea that certain similarities in the original organization of these X chromosomes could have facilitated their later enlargement.