A Genomic House of Mirrors

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Science  02 Nov 2001:
Vol. 294, Issue 5544, pp. 959
DOI: 10.1126/science.294.5544.959a

Certain inherited forms of human male infertility are associated with small deletions in the long arm of the Y chromosome, which result in defective sperm production. These deletions occur most often in a genomic region called AZFc (for azoospermia factor c). The putative fertility factors encoded within AZFc are of great interest, but this region of the Y chromosome has posed an enormous challenge to conventional sequencing efforts because it is unusually rich in repetitive DNA.

Kuroda-Kawaguchi et al. have accepted this challenge and now describe the complete nucleotide sequence and extraordinary structural features of AZFc. The region consists of six distinct families of amplicons (very large repeats), organized in three palindromes, including one that spans three megabases and shows almost perfect arm-to-arm identity. Encoded within these palindromes are 27 transcription units that are selectively expressed in the testis. Based on the sequence information, the authors speculate that the AZFc deletions found in infertile men arise by homologous recombination. The scale and precision of the symmetries within AZFc are unprecedented and raise intriguing questions about the evolutionary origin of this genomic region and the selective pressures that maintain it.—PAK

Nature Genet., 10.1038/ng757.

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