MBE Advance Access published online on October 6, 2009
Molecular Biology and Evolution, doi:10.1093/molbev/msp231
Research Article |
Footprints of X-to-Y gene conversion in recent human evolution
1 Dipartimento di Genetica e Biologia Molecolare, Sapienza Università di Roma, 00185, Rome, Italy
2 Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, CA 94304, USA
3 Istituto di Biologia e Patologia Molecolari, Consiglio Nazionale delle Ricerche, 00185, Rome, Italy
* Corresponding Author: Rosaria Scozzari, Dipartimento di Genetica e Biologia Molecolare, Sapienza Università di Roma, P.le Aldo Moro 5, 00185 Rome, Italy, Phone: (39) 06 49912826 (office), Phone: (39) 06 49912924 (lab), Fax: (39) 06 4456866, E-mail: rosaria.scozzari{at}uniroma1.it
Received for publication June 8, 2009. Revision received September 4, 2009. Accepted for publication September 23, 2009.
Different X-homologous regions of the male specific portion of the human Y chromosome (MSY) are characterized by a different content of putative SNPs, as reported in public databases. The possible role of X-to-Y non allelic gene conversion in contributing to these differences remains poorly understood. We explored this issue by analyzing sequence variation in three regions of the MSY characterized by a different degree of X-Y similarity and a different density of putative SNPs: the PCDH11Y gene in the X-transposed (X-Y identity 99%, high putative SNP content); the TBL1Y gene in the X-degenerate (X-Y identity 86%-88%, low putative SNP content) and VCY genes-containing region in the P8 palindrome (X-Y identity 95%, low putative SNP content). Present findings do not provide any evidence for gene conversion in the PCDH11Y and TBL1Y genes; they also strongly suggest that most putative SNPs of the PCDH11Y gene (and possibly the entire X-transposed region) are most likely X-Y paralogous sequence variants, which have been entered in the databases as SNPs. On the other hand, clear evidence for the VCY genes in the P8 palindrome having acted as an acceptor of X-to-Y gene conversion was obtained. A rate of 1.8 x 10-7 X-to-Y conversions/bp/year was estimated for these genes. These findings indicate that in the VCY region of the MSY, X-to-Y gene conversion can be highly effective to increase the level of diversity among human Y chromosomes, and suggest an additional explanation for the ability of the Y chromosome to retard degradation during evolution. Present data are expected to pave the way for future investigations on the role of non-allelic gene conversion in double strand break repair and the maintenance of Y chromosome integrity.
Key Words: gene conversion hotspot • MSY • segmental duplications • human sex chromosomes • dbSNP
These authors contributed equally to this work