Rodent of the Week: How labor begins

The start of labor has always been something of a mystery. How does the body know when it’s time to send junior out of his or her watery cocoon and into the real world? Clues have trickled in over the last several decades. A study published this week identifies another piece of the puzzle.

Hormones are known to be involved as a trigger to labor. But researchers at the University of Texas Southwestern Medical Center discovered that small molecules called microRNAs work with hormones to control the onset of labor. The scientists measured the levels in the uteri of mice in mid-pregnancy and again when they were near labor.

As the time of labor drew nearer, a particular group of microRNA controlled by the hormone progesterone -- called the miR-200 family -- increased. The miR-200s block the production of two proteins, ZEB1 and ZEB2 that normally rise in response to progesterone. So when the ZEB1 and ZEB2 proteins are suppressed, progesterone action decreases and the genes that control contractions turn on, researchers found. In contrast, as long as progesterone is present, contractions are prevented.

The research could help doctors create RNA-based drugs that could prevent preterm labor, said the senior author of the study, Dr. Carole Mendelson of Southwestern Medical Center.

“We’ve been struggling for a long time to understand how progesterone keeps the uterus from contracting during most of pregnancy,” Mendelson said in a news release. “With these findings, we understand better the system that controls labor, so with future research we might have the potential to manipulate it and prevent preterm birth.”

The study appears online Monday in the Proceedings of the National Academy of Sciences.

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