A gene essential to the growth and development of most organ systems in the body also is vital to female but not male embryonic sexual development, scientists report this month.
The study, from researchers at the University of Illinois and the University of Texas, appears in Human Molecular Genetics. The findings lend support to a controversial hypothesis about mammalian sexual development.
In the beginning in terms of their sexual organs all embryos look alike, said Illinois veterinary biosciences professor Humphrey Yao, who led the study.
"They have a common primordium, the foundation for both testis and ovary," he said. "Only at a certain stage of development does this primordium start to follow a different path."
In the early days of research into sexual development, it was thought that all females had two X chromosomes, all males had an X and a Y, and that the Y made all the difference. Unless it had a Y chromosome, an embryo developed ovaries and became female, more or less by default, scientists thought. They even found a specific gene on the Y chromosome, called SRY (for sex-determining region of the Y chromosome) that appeared to be essential for testes formation.
But when researchers discovered some rare cases of individuals who developed testes even though they had two X chromosomes and no Y chromosome or SRY gene, they realized that the mechanisms of sex determination were more complex than previously thought.
This led to a new theory, called the "Z" hypothesis, which proposed that testes development was actually the default pathway. According to this theory, an unknown gene or process, called "Z," could disrupt this pathway and lead to the development of ovaries.
The "Z" hypothesis explained why SRY appeared essential for testes development. When it is present, SRY suppresses "Z" and allows the default option (development of testes) to occur.
This theory was comp
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University of Illinois at Urbana-Champaign