Mother helps set fetal biological clock ^{CEFR B1}

The study, published in the Journal of Biological Rhythms and led by researchers at Washington University in St. Louis, developed a way to observe clock activity in fetuses. The team used genetically engineered mice in which a clock protein was tagged with luciferase, a light-producing protein. When a male carrying the tagged protein mated with an untagged female, the fetuses carried the tag while the mother did not. Pregnant mice drank water with a chemical that made luciferase emit light, and sensitive cameras recorded the fetuses glowing whenever the clock protein was active.

The researchers found clear day–night rhythms in the pups that synchronized to the mother's rest–activity cycle during the last week of pregnancy, a period equivalent to the third trimester in humans. They also detected daily rhythms across the placenta before the fetus can sense light, suggesting the mother sends timing cues. The team linked timing to maternal glucocorticoid hormones, which cross the placenta and may set the fetal clock. Giving synthetic glucocorticoids made pups' clocks synchronize to local time more quickly; the authors note that these drugs are routinely given to pregnant people at risk of preterm birth and that timing may matter.

The study also saw a strong association between failure to develop circadian clock gene activity in fetuses and failure to deliver, though it is not yet clear whether lack of rhythms causes problems or reflects them. The work was supported by the National Institutes of Health and the March of Dimes Prematurity Research Center; KLN received a McDonnell Center fellowship.