Next Article in Journal
HiCNN2: Enhancing the Resolution of Hi-C Data Using an Ensemble of Convolutional Neural Networks
Previous Article in Journal
Transcriptional Structure of Petunia Clock in Leaves and Petals
Open AccessArticle

ZW Sex Chromosomes in Australian Dragon Lizards (Agamidae) Originated from a Combination of Duplication and Translocation in the Nucleolar Organising Region

1
Institute for Applied Ecology, Faculty of Science and Technology, University of Canberra, Canberra ACT 2617, Australia
2
Department of Genetics, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand
*
Author to whom correspondence should be addressed.
Current Address: Department of Biomedical Chemistry, Kwansei Gakuin University, Hyogo 669-1337, Japan.
Genes 2019, 10(11), 861; https://doi.org/10.3390/genes10110861
Received: 23 September 2019 / Revised: 22 October 2019 / Accepted: 29 October 2019 / Published: 30 October 2019
(This article belongs to the Section Population and Evolutionary Genetics and Genomics)
Sex chromosomes in some reptiles share synteny with distantly related amniotes in regions orthologous to squamate chromosome 2. The latter finding suggests that chromosome 2 was formerly part of a larger ancestral (amniote) super-sex chromosome and raises questions about how sex chromosomes are formed and modified in reptiles. Australian dragon lizards (Agamidae) are emerging as an excellent model for studying these processes. In particular, they exhibit both genotypic (GSD) and temperature-dependent (TSD) sex determination, show evidence of transitions between the two modes and have evolved non-homologous ZW sex microchromosomes even within the same evolutionary lineage. They therefore represent an excellent group to probe further the idea of a shared ancestral super-sex chromosome and to investigate mechanisms for transition between different sex chromosome forms. Here, we compare sex chromosome homology among eight dragon lizard species from five genera to identify key cytological differences and the mechanisms that may be driving sex chromosome evolution in this group. We performed fluorescence in situ hybridisation to physically map bacterial artificial chromosome (BAC) clones from the bearded dragon, Pogona vitticeps’ ZW sex chromosomes and a nucleolar organising region (NOR) probe in males and females of eight Agamid species exhibiting either GSD or TSD. We show that the sex chromosome derived BAC clone hybridises near the telomere of chromosome 2q in all eight species examined. This clone also hybridises to the sex microchromosomes of three species (P vitticeps, P. barbata and Diporiphora nobbi) and a pair of microchromosomes in three others (Ctenophorus pictus, Amphibolurus norrisi and Amphibolurus muricatus). No other chromosomes are marked by the probe in two species from the closely related genus Physignathus. A probe bearing nucleolar organising region (NOR) sequences maps close to the telomere of chromosome 2q in all eight species, and to the ZW pair in P. vitticeps and P. barbata, the W microchromosome in D. nobbi, and several microchromosomes in P. cocincinus. Our findings provide evidence of sequence homology between chromosome 2 and the sex chromosomes of multiple agamids. These data support the hypothesis that there was an ancestral sex chromosome in amniotes that gave rise to squamate chromosome 2 and raises the prospect that some particular property of this chromosome has favoured its role as a sex chromosome in amniotes. It is likely that the amplification of repetitive sequences associated with this region has driven the high level of heterochromatinisation of the sex-specific chromosomes in three species of agamid. Our data suggest a possible mechanism for chromosome rearrangement, including inversion and duplication near the telomeric regions of the ancestral chromosome 2 and subsequent translocation to the ZW sex microchromosomes in three agamid species. It is plausible that these chromosome rearrangements involving sex chromosomes also drove speciation in this group. View Full-Text
Keywords: chromosome rearrangements; NOR; evolution; BAC; gene mapping; FISH (fluorescence in situ hybridisation); comparative genomics chromosome rearrangements; NOR; evolution; BAC; gene mapping; FISH (fluorescence in situ hybridisation); comparative genomics
Show Figures

Figure 1

MDPI and ACS Style

Matsubara, K.; O’Meally, D.; Sarre, S.D.; Georges, A.; Srikulnath, K.; Ezaz, T. ZW Sex Chromosomes in Australian Dragon Lizards (Agamidae) Originated from a Combination of Duplication and Translocation in the Nucleolar Organising Region. Genes 2019, 10, 861.

Show more citation formats Show less citations formats
Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here.

Article Access Map by Country/Region

1
  • Supplementary File 1:

    ZIP-Document (ZIP, 398 KB)

  • Externally hosted supplementary file 1
    Doi: 10.5281/zenodo.3457628
    Link: https://zenodo.org/deposit/3457628
    Description: Please attached supplementary tables because reviewer 1 was unable to access the online version. Response: added as zip files under supplementary file section.
Back to TopTop