Human Molecular Genetics Advance Access originally published online on May 26, 2004
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Human Molecular Genetics, 2004, Vol. 13, No. 14 1421-1431
DOI: 10.1093/hmg/ddh161
Human Molecular Genetics, Vol. 13, No. 14 © Oxford University Press 2004; all rights reserved
Six5 is required for spermatogenic cell survival and spermiogenesis
Institute for Genetic Medicine, Room 240, University of Southern California, Keck School of Medicine, 2250 Alcazar Street, Los Angeles, CA 90033, USA
Received February 8, 2004; Accepted May 14, 2004
Myotonic dystrophy 1 (DM1) is a multi-system disorder characterized by endocrine defects that include testicular and tubular atrophy, oligospermia, Leydig cell hyperproliferation and increased follicle stimulating hormone (FSH) levels. DM1 results from a CTG expansion that causes transcriptional silencing of the flanking SIX5 allele. Loss of Six5 results in male sterility and a progressive decrease in testicular mass with age. We demonstrate a strict requirement of Six5 for both spermatogenic cell survival and spermiogenesis. Leydig cell hyperproliferation and increased intra-testicular testosterone levels are observed in the Six5/mice. Although increased FSH levels are observed in the Six5+/and Six5/mice, serum testosterone levels and intra-testicular inhibin alpha and inhibin beta B levels are not altered in the Six5 mutant animals when compared with controls. Significantly, steady-state c-Kit levels are reduced in the Six5/ testis. Thus, decreased c-Kit levels could contribute to the elevated spermatogenic cell apoptosis and Leydig cell hyperproliferation in the Six5/ mice. The results support the hypothesis that the reduced SIX5 levels contribute to the male reproductive defects in DM1.
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