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The ZW sex microchromosomes of an Australian dragon lizard share no homology with those of other reptiles or birds

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Abstract

Reptiles show a diverse array of sex chromosomal systems but, remarkably, the Z sex chromosomes of chicken are homologous to the ZW sex chromosomes of a species of gecko, Gekko hokouensis, suggesting an ancient but common origin. This is in contrast to the ZW sex chromosomes of snakes and a species of soft-shelled turtle, Pelodiscus sinensis, which are nonhomologous to those of chicken or each other and appear to have been independently derived. In this paper, we determine what homology, if any, the sex chromosomes of the Australian dragon lizard Pogona vitticeps shares with those of snake and chicken by mapping the dragon homologs of five snake Z chromosome genes (WAC, KLF6, TAX1BP1, RAB5A, and CTNNB1) and five chicken Z chromosome genes (ATP5A1, GHR, DMRT1, CHD1, and APTX) to chromosomes in the dragon. The dragon homologs of snake and chicken sex chromosome genes map to chromosomes 6 and chromosome 2, respectively, in the dragon and that DMRT1, the bird sex-determining gene, is not located on the sex chromosomes of P. vitticeps. Indeed, our data show that the dragon homolog to the chicken Z chromosome is likely to be wholly contained within chromosome 2 in P. vitticeps, which suggests that the sex-determining factor in P. vitticeps is not the sex-determining gene of chicken. Homology between chicken Z chromosome and G. hokouensis ZW chromosome pairs has been interpreted as retention of ancient ZW sex chromosomes in which case the nonhomologous sex chromosomes of snake and dragons would be independently derived. Our data add another case of independently derived sex chromosomes in a squamate reptile, which makes retention of ancient sex chromosome homology in the squamates less plausible. Alternatively, the conservation between the bird Z chromosome and the G. hokouensis ZW chromosomes pairs is coincidental, may be an example of convergent evolution, its status as the Z chromosome having been independently derived in birds and G. hokouensis.

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Abbreviations

BAC:

bacterial artificial chromosomes

DAPI:

4′,6-diamidino-2-phenylindole

dATP:

2′-deoxyadenosine 5′-triphosphate

dCTP:

2′-deoxycytidine 5′-triphosphate

dGTP:

2′-deoxyguanosine 5′-triphosphate

DNA:

deoxyribonucleic acid

dNTP:

deoxynucleotide triphosphate

dUTP:

2′-deoxyuridine 5′-triphosphate

FISH:

fluorescent in situ hybridization

GSD:

genotypic sex determination

HEPES:

4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid

Overgo:

overlapping oligonucleotides

PCR:

polymerase chain reaction

SSC:

standard saline citrate

TSD:

temperature-dependent sex determination

v/v :

volume/volume

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Acknowledgements

We thank Vidushi Patel and Denis O'Meally for the assistance in the laboratory. All experiments were performed with the approval of the University of Canberra Animal Experimentation Ethics Committee (Proposal CEAE 04/04). This work is supported by the Australian Research Council Discovery Grant (DP0881196) awarded to S.S., A.G., and Scott V. Edwards.

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Authors and Affiliations

  1. Institute for Applied Ecology, University of Canberra, Canberra, Australia

    Tariq Ezaz, Arthur Georges & Stephen D. Sarre

  2. Research School of Biology, Australian National University, Canberra, Australia

    Tariq Ezaz, Benjamin Moritz, Paul Waters & Jennifer A. Marshall Graves

  3. Institute for Applied Ecology, University of Canberra, Building 3, Bruce, ACT, 2616, Australia

    Tariq Ezaz

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  1. Tariq Ezaz
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  2. Benjamin Moritz
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  3. Paul Waters
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  4. Jennifer A. Marshall Graves
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  5. Arthur Georges
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  6. Stephen D. Sarre
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Correspondence to Tariq Ezaz.

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Responsible Editor: Herbert Macgregor.

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Ezaz, T., Moritz, B., Waters, P. et al. The ZW sex microchromosomes of an Australian dragon lizard share no homology with those of other reptiles or birds. Chromosome Res 17, 965–973 (2009). https://doi.org/10.1007/s10577-009-9102-6

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  • DOI: https://doi.org/10.1007/s10577-009-9102-6

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