The First Identification of Homomorphic XY Sex Chromosomes by Integrating Cytogenetic and Transcriptomic Approaches in Plestiodon elegans (Scincidae).

The sex chromosomes of skinks are usually poorly differentiated and hardly distinguished by cytogenetic methods. Therefore, identifying sex chromosomes in species lacking easily recognizable heteromorphic sex chromosomes is necessary to fully understand sex chromosome diversity. In this paper, we employed cytogenetics, sex quantification of genes, and transcriptomic approaches to characterize the sex chromosomes in Plestiodon elegans. Cytogenetic examination of metaphases revealed a diploid number of 2n = 26, consisting of 12 macrochromosomes and 14 microchromosomes, with no significant heteromorphic chromosome pairs, speculating that the sex chromosomes may be homomorphic or poorly differentiated. The results of the sex quantification of genes showed that Calumenin (calu), COPI coat complex subunit γ 2 (copg2), and Smoothened (smo) were at half the dose in males as in females, suggesting that they are on the X chromosome. Transcriptomic data analysis from the gonads yielded the excess expression male-specific genes (n = 16), in which five PCR molecular markers were developed. Restricting the observed heterozygosity to males suggests the presence of homomorphic sex chromosomes in P. elegans, XX/XY. This is the first breakthrough in the study of the sex chromosomes of Plestiodon.

Complete sequence and organization of the mitochondrial genome of Cyclemys atripons (Testudines, Geoemydidae)

The Black Bridged Leaf Turtle, Cyclemys atripons (Testudines; Cryptodira; Geoemydidae), is a poorly known species within the genus Cyclemys. We determined the complete nucleotide sequence of the Cyclemys atripons mitochondrial genome (mtDNA) and found it to be 16,500 base pairs (bp) in length, with the genome organization, gene order and base composition being identical to that of the typical vertebrate. However, unlike for most turtle mtDNA so far reported, an extra base was not found in the NADH3 gene. The C. atripons control region of mtDNA was 981 bp long. Comparisons with three other geoemydids showed that the C. atripons control region contained a highly variable region at the 3' end composed of AT enriched tandem repeats containing a fifteen-unit 5'-A (AT)3-3' variable number of tandem repeats (VNTRs).

Isolation and sequencing of doublesex/male abnormal 3 (DM) related transcription factor (Dmrt) genes from the Asian toad Bufo gargarizans (Cantor, 1842)

The doublesex/male abnormal 3 (dsx/mab-3 or DM) domain gene family involved in sexual development encodes putative transcription factors including a DNA-binding homology motif, the DM domain. We used highly degenerate primers to clone and sequence seven distinct DM related transcription factor (Dmrt) genes from the Asian toad (Bufo gargarizans Cantor, 1842). A database search for the cloned sequences revealed the following percentage identity with the homologous Dmrt genes of the human: BgDmrt1 = 97 percent, BgDmrt2 = 97 percent, three isoforms of BgDmrt3 (BgDmrt3a = 93 percent, BgDmrt3b = 95 percent, BgDmrt3c = 100 percent) and two isoforms of BgDmrt5 (BgDmrt5 = 97 percent, BgDmrt5 = 91 percent). Based on DM domain amino acid sequence similarities we constructed a phylogenetic tree which grouped vertebrate and invertebrate Dmrt genes into seven distinct subfamilies. The DM domains of both human and the newly-discovered Bufo gargarizans genes contained two conserved zinc-chelating sites (CCHC and HCCC), except BgDmrt3b, which contained the CCRC and HCCC sites.

Isolation and sequencing of seven Sox genes from the lacertid lizard Eremias breuchleyi

The Sox family of genes shares a high sequence similarity with the HMG box region of the human Y chromosomal gene, SRY. We used highly degenerate primers to clone and sequence seven Eremias breuchleyi Sox genes (EbSox2, EbSox3, EbSox4, EbSox11, EbSox12, EbSox14 and EbSox21). A database search for the cloned sequences revealed the following percentage identity with the homologous human SOX genes: EbSox2 = 96 percent, EbSox3 = 88 percent, EbSox4 = 94 percent, EbSox11 = 99 percent, EbSox12 = 96 percent, EbSox14 = 98 percent, EbSox21 = 97 percent. Cluster analysis indicates that they seem to belong to group B and group C of Sox gene family, respectively.