Mother helps set fetal biological clock ^{CEFR B2}

New research shows that maternal signals help set the fetal circadian clock while the fetus is still in the womb. The team, reporting in the Journal of Biological Rhythms and led by researchers at Washington University in St. Louis, used genetically engineered mice with a clock protein tagged to luciferase, a light-producing protein. By mating a tagged male with a normal female, the researchers produced fetuses that carried the tag while the mother did not. They added a chemical to the pregnant mice's drinking water that causes luciferase to emit light, and sensitive cameras recorded pulses of light when the fetal clock protein was active.

Clear day–night rhythms appeared in the pups and synchronized to the mother's rest–activity cycle during the last week of pregnancy, a period equivalent to the third trimester in humans. Daily rhythms were also detected across the placenta before the fetus can sense light, indicating that the mother sends timing cues. The team linked timing to maternal glucocorticoid hormones, which normally rise and fall across the day and cross the placenta. When researchers administered synthetic glucocorticoids to pregnant mice, the pups' clocks synchronized to local time more quickly; the authors point out that such drugs are routinely used in people at risk of preterm birth and that the timing of administration may matter.

Researchers also observed a strong association between absent circadian clock gene activity in fetuses and failure to deliver. They caution that it is not yet known whether lack of rhythms causes developmental problems or simply reflects them, but the link suggests clock activity is connected to healthy fetal development. The study notes that over 80% of the world's population is exposed to artificial light at night, which can disrupt daily rhythms. Funding came from the National Institutes of Health and the March of Dimes Prematurity Research Center; KLN received a McDonnell Center fellowship.