Remnant of Unrelated Amniote Sex Chromosomal Linkage Sharing on the Same Chromosome in House Gecko Lizards, Providing a Better Understanding of the Ancestral Super-Sex Chromosome

Abstract

Comparative chromosome maps investigating sex chromosomal linkage groups in amniotes and microsatellite repeat motifs of a male house gecko lizard (Hemidactylus frenatus, HFR) and a flat-tailed house gecko lizard (H. platyurus, HPL) of unknown sex were examined using 75 bacterial artificial chromosomes (BACs) from chicken and zebra finch genomes. No massive accumulations of microsatellite repeat motifs were found in either of the gecko lizards, but 10 out of 13 BACs mapped on HPL chromosomes were associated with other amniote sex chromosomes. Hybridization of the same BACs onto multiple different chromosome pairs suggested transitions to sex chromosomes across amniotes. No BAC hybridization signals were found on HFR chromosomes. However, HFR diverged from HPL about 30 million years ago, possibly due to intrachromosomal rearrangements occurring in the HFR lineage. By contrast, heterochromatin likely reshuffled patterns between HPL and HFR, as observed from C-positive heterochromatin distribution. Six out of ten BACs showed partial homology with squamate reptile chromosome 2 (SR2) and snake Z and/or W sex chromosomes. The gecko lizard showed shared unrelated sex chromosomal linkages—the remnants of a super-sex chromosome. A large ancestral super-sex chromosome showed a correlation between SR2 and snake W sex chromosomes.

Cytogenetic Analysis of Seven Species of Gekkonid and Phyllodactylid Geckos

“…The topology of ITRs differs significantly among species, e.g., even between the congeneric Gekko badenii, Gekko hokouensis, and Gekko cf. lionotum, a pattern previously observed in other reptilian lineages [59][60][61]. Comparative chromosome painting or comparison of chromosome-level genome assemblies is required to identify the origin of these ITRs.…”

“…In addition, telomeric-like repeats often form a part of the centromeric microsatellite content, and these are not necessarily connected to chromosome rearrangements [58]. ITRs have been detected in many vertebrate taxa, including more than 100 species of lizards, snakes, and turtles (reviewed in [59,60]), including the gekkonids Agamura persica, Cyrtopodion scabrum, Gekko hokouensis, Hemidactylus platyurus, Paroedura bastardi, and Paroedura stumpffi, and the phyllodactylid Gymnodactylus amarali [7,59,61]. In the current study, we identified ITRs in an additional five gekkonid species: Blaesodactylus boivinii, Gekko badenii, Gekko cf.…”