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The Sensitive Y

Researchers from Case Western Reserve University in Ohio report in the Proceedings of the National Academy of Sciences that the human Y chromosome is sensitive to environmental factors. Michael Weiss and his colleagues examined clinical mutations in SRY, the sex-determining region of the Y chromosome, focusing on variants inherited by XY sterile daughters from fertile fathers.

From their analyses, Weiss and his team gather that two variants, V60L and I90M in the high-mobility group box affected nucleocytoplasmic shuttling, leading to decreased levels of activated SRY in the nucleus. In turn, the researchers say, that leads to reduced occupancy of site regulating Sertoli-cell differentiation. "Our results demonstrate that nucleocytoplasmic shuttling of SRY is necessary for robust initiation of testicular development," the group adds.

This sensitivity of SRY leads to a range of testosterone-related male attributes that vary among men and that likely have an evolutionary purpose, Weiss tells the New York Times. "This tenuous switch is what underlies the variability of testosterone secretion in utero," he adds.