He teamed with Edwin Chapman, a Howard Hughes Medical Institute investigator, fellow SMPH physiology professor and synaptotagmin expert. The UW-Madison researchers conducted high-powered biophysical measurements to understand exactly what Syt IV does in the pituitary. They made a thorough comparison of the pituitaries from normal mice and mice in which Syt IV had been knocked out.
The work showed conclusively that, like other members of the synaptotagmin family, Syt IV resides on vesicles. But unlike the others, Syt IV doesn't trigger neurotransmitter or hormone release.
"It does not simply translate a calcium signal into a command for hormone release," says Jackson. "Unlike other synaptotagmins, Syt IV tunes the triggering command and determines whether the same electrical impulse will let a large or small amount of hormone out of the nerve terminal."
This ability to modulate hormone release may have important implications for pregnancy, birth, lactation and the menstrual cycle, all of which are linked to fluctuations in oxytocin levels.
"Any change in the body that entails releasing more or less of this hormone into the bloodstream could well be a result of the brain's making more or less of this protein," says Jackson, who for two decades has studied the powerful pea-sized pituitary located at the base of the brain.
For example, early release of oxytocin can lead to premature birth, a phenomenon that has intrigued Jackson for a long time.
"It's quite possible that Syt IV levels change during pregnancy, birth and even post partum," he conjectures.
Confirming the possibility will be the next order of business for the Wisconsin researchers and others.
Jackson's interest in the effects of oxytocin, also known as the "love hormone," is not restricted
|Contact: Dian Land|
University of Wisconsin-Madison