In an online article published on September 9, 2016 in Scientific Reporets, Hokkaido University researchers have revealed that key sex-determining genes continue to operate in a mammalian species that lacks the Y chromosome, taking us one step farther toward understanding sex differentiation. The open-access article is titled “Molecular Mechanism of Male Differentiation Is Conserved in the SRY-Absent Mammal, Tokudaia osimensis.” In most placental mammals, the Y chromosome induces male differentiation during development, whereas embryos without it become female. The sex-determining gene SRY is present on the Y chromosome and induces other regulatory genes that suppress female differentiation. The Amami spiny rat (Tokudaia osimensis) is exceptional as it lacks a Y chromosome and thus the SRY gene, raising the question as to how male differentiation can still occur in this animal. Tomofumi Otake, Ph.D., and Asako Kuroiwa, Ph.D., of Hokkaido University in Japan performed gene mapping to determine the chromosomal locations of sex-related genes in the T. osimensis genome. They then compared T. osimensis nucleotide and amino acid sequences of T. osimensis with those of the mouse and other rats. Furthermore, using cultured cells, the scientists examined how the sex-related genes were regulated. SRY has been well-investigated in previous research and is known to turn on a range of regulatory genes such as Sox9 and AMH that play an important role in male differentiation. The team’s results suggest that, even though there is no SRY gene in T. osimensis , the regulatory genes that SRY normally turns on are present and operate as they do in other placental mammals. “We speculate that there is an unknown gene that acts as a substitute for SRY in T. osimensis,” says Professor Kuroiwa.
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