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Men have XY sex chromosomes, and the development of testes is thought to occur after upregulation (an increase in cellular components) on the testicular SOX9 gene pathway.
However, how this testicular SOX9 upregulation occurs has been unclear.
In this new study, Dr Jacqueline Hewitt and colleagues from the Royal Children's Hospital Melbourne, Australia, began by examining the genomes of 30 children with disorders of sex development (DSD).
Nine patients had 46,XX testicular DSD - meaning, although they had XX chromosomes, they had developed as males with testicles; 21 patients had 46,XY gonadal dysgenesis - meaning, although they had XY chromosomes, they had developed as females, without testicles.
In two of the patients with 46,XX testicular DSD, researchers found a small region, outside of the SOX9 gene, which was duplicated. Analysis of this duplicated region showed that it contained an SRY/SOX sequence, a region that may regulate SOX9 gene activity and therefore be involved in testicle formation.
The arrangement of the duplications implies they have either a dosage-related or structural effect on the SOX9 gene. The position of these duplications ties in with previous research in patients with a similar condition, familial 46,XX testicular DSD, which also revealed that this chromosome region may be involved in testes development.
These results help address the complex gene regulation system that controls human sex development, in particular the mechanism by which the SOX9 gene is upregulated and testicles are formed in the embryo.
This new gene regulatory region appears to be a missing link in the testis development system, and it is significant that duplications in this region can initiate the development of testicles in a person who has XX chromosomes.
More studies are needed to determine if testis development can be initiated by switching on this region in growing cells and in developmental animal models.
Researcher Dr Jacqueline Hewitt, from the Royal Children's Hospital Melbourne, Australia:
"We have known for a while that for testes to form in the embryo, a key gene called SOX9 needs to be activated. However, until now, the mechanism by which this activation occurs has been unclear.
"Our research indicates that there is a gene regulatory region on chromosome 17, upstream of the SOX9 gene, which is involved in the initiation of testicle development in the foetus. This regulatory region is sited a distance away from the SOX9 gene itself, but functions to switch the gene on, allowing the formation of testicles.
This illustrates the fundamental importance of not just the actual genes, but also of gene regulation systems in human development.
We are only now beginning to understand the mechanisms of gene regulation, which are essential for the development of a complex organism such as a human child. This research significantly advances our understanding of how the testes develop in the human body."
Original article: http://www.eurekalert.org/pub_releases/2011-09/esfp-ngr092511.php