The dragon lizard Pogona vitticeps has ZZ/ZW micro-sex chromosomes
- 684 Downloads
The bearded dragon, Pogona vitticeps (Agamidae: Reptilia) is an agamid lizard endemic to Australia. Like crocodilians and many turtles, temperature-dependent sex determination (TSD) is common in agamid lizards, although many species have genotypic sex determination (GSD). P. vitticeps is reported to have GSD, but no detectable sex chromosomes. Here we used molecular cytogenetic and differential banding techniques to reveal sex chromosomes in this species. Comparative genomic hybridization (CGH), GTG- and C-banding identified a highly heterochromatic microchromosome specific to females, demonstrating female heterogamety (ZZ/ZW) in this species. We isolated the P. vitticeps W chromosome by microdissection, re-amplified the DNA and used it to paint the W. No unpaired bivalents were detected in male synaptonemal complexes at meiotic pachytene, confirming male homogamety. We conclude that P. vitticeps has differentiated previously unidentifable W and Z micro-sex chromosomes, the first to be demonstrated in an agamid lizard. Our finding implies that heterochromatinization of the heterogametic chromosome occurred during sex chromosome differentiation in this species, as is the case in some lizards and many snakes, as well as in birds and mammals. Many GSD reptiles with cryptic sex chromosomes may also prove to have micro-sex chromosomes. Reptile microchromosomes, long dismissed as non-functional minutiae and often omitted from karyotypes, therefore deserve closer scrutiny with new and more sensitive techniques.
Key wordsagamid CGH comparative genomic hybridization heterochromatinization microchromosomes sex chromosomes
Unable to display preview. Download preview PDF.
- Bull JJ (1983) Evolution of Sex Determining Mechanisms. Menlo Park, California: Benjamin/Cummings.Google Scholar
- Cogger HG (1996) Reptiles and Amphibians of Australia. Australia: Reed Books.Google Scholar
- Donnellan (1985) The Evolution of Sex Chromosomes in Scincid Lizards. PhD thesis. Macquarie University, Sydney.Google Scholar
- Ezaz MT, McAndrew BJ, Penman DJ (2004) Spontaneous diploidization of maternal chromosome set in Nile tilapia (Oreochromis niloticus) eggs. Aquaculture Res 35: 271–277.Google Scholar
- Gorman GC (1973) The chromosomes of the Reptilia, a cytotaxonomic interpretation. In: Chiarelli AB, Capanna E, eds. Cytotaxonomy and Vertebrate Evolution. London, New York: Academic Press, pp. 349–424.Google Scholar
- Harlow PS (2001) The ecology of sex-determining mechanisms in Australian agamid lizards. PhD Thesis. School of Biological Sciences. Macquarie University, Sydney.Google Scholar
- Harvey SC, Campos-Ramos R, Kennedy DD et al. (2002) Karyotype evolution in tilapia: mitotic and meiotic chromosome analysis of Oreochromis karongae and O. niloticus × O. karongae hybrids. Genetica 15: 169–177.Google Scholar
- ISCN (1985) An International System for Human Cytogenetics Nomenclature: Birth Defects. Original article series. 1985, vol 21, No. 1. March of Dimes Birth Defects Foundation, NY.Google Scholar
- Olmo E (1986) A. Reptilia. In: John B, ed. Animal Cytogenetics 4 Chordata 3. Gebruder Berlin-Stuttgart: Bortraeger.Google Scholar
- Olmo E, Signorino G (2005) Chromorep: a reptile chromosomes database. Internet references. Retrieved fromhttp://126.96.36.199/professori/chromorep.pdf, 2.10.05.
- Olmo E, Cobror O, Morescalchi A, Odierna G (1984) Homomorphic sex chromosomes in lacertid lizard Takydromus sexlineatus. Heredity 53: 457–459.Google Scholar
- Ray-Chaudhury SP, Singh L, Sharma T (1971) Evolution of sex chromosomes and formation of W chromatin in snakes. Chromosoma 33: 239–251.Google Scholar
- Singh L, Purdom IF, Jones KW (1976) Satellite DNA and evolution of sex chromosomes. Chromosoma 76: 137–157.Google Scholar
- Traut W, Eickhoff U, Schorch J (2001) Identification and analysis of sex chromosomes by comparative genomic hybridization (CGH). Meth Cell Sci 23: 155–161.Google Scholar
- Uetz P (2005) The EMBL reptile database. Internet references. Retrieved from:http://www.reptile-database.org, 2.10.05.
- Verma RS, Babu A (1995) Human Chromosomes: Principles and Techniques, Second Edition. New York: McGraw-Hill, Inc.Google Scholar
- Witten JG (1983) Some karyotypes of Australian agamids (Reptilia: Lacertilia). Austral J Zool 31: 533–540.Google Scholar
- Zeng X-M, Wang Y-Z Liu Z-J et al. (1997) Karyotypes on nine species in the genus Phrynocephalus, with discussion of karyotypic evolution of Chinese Phrynocephalus. Acta Zool Sinica 43: 399–410.Google Scholar