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New master switch found in the brain that regulates appetite and reproduction
Date:8/31/2008

insulin resistant. "Their hormones and blood sugar resembled that seen in humans with these disorders," Montminy says.

They also discovered, to their surprise, that mice of both sexes were infertile; the uteri and ovaries in female mice were anatomically dysfunctional, for example. "We don't study infertility, but we put two and two together," he says. "We knew leptin is the critical hormone for regulating body weight, and that it is also very important for regulating reproduction."

Altarejos discovered that TORC1, which is found within nerve cells, responds to signals from leptin, which binds to receptors on the outside of the same cells. TORC1 then turns on a spate of genes, two of which are well known. One is the CART (Cocaine and Amphetamine Regulated Transcript) gene that is known to stifle appetite. The other, KISS1 (named by its discoverers at the Penn State Hershey Medical Center) is required for reproduction; mutations in the gene produce human infertility.

So when leptin binds with its receptor on brain cells, it turns on TORC1, which, in turns activates CART to suppress appetite, because more food is not needed, and KISS1, signaling reproduction can now commence in this well-fed body. Conversely, when leptin is not activating brain receptors, TORC1 is turned off, as are CART and KISS1.

They also discovered that when mice inherit only one TORC1 gene (instead of the normal two, one from each parent), fertility is restored but the mice gain more weight than normal mice. "This suggests that half of the dose of TORC switch is enough to cause problems in leptin signaling in the brain, and it may be that subtle mutations in TORC1 in humans could be responsible for an inheritable risk factor for gaining weight," Montminy says.

Tweaking mutated and inefficient TORC genes may be possible through drug therapy, he adds. "TORC1 is regulated by phosphate handling enzymes called kinases, and kinases often make for very good drug targ
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Contact: Gina Kirchweger
Kirchweger@salk.edu
858-453-4100 x1340
Salk Institute
Source:Eurekalert

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