The uterus sustains stable biological clock during pregnancy

Area of Science:

• Chronobiology
• Reproductive Biology
• Developmental Physiology

Background:

• Maternal circadian rhythms influence fetal development, primarily through hormones and nutrition.
• The role of pregnant reproductive organs' intrinsic circadian properties in fetal development remains under-investigated.

Purpose of the Study:

• To investigate the circadian functions of the pregnant rat uterus and placenta.
• To determine if reproductive organs serve as a source of circadian information for the developing fetus.

Main Methods:

• Utilized Period1-luciferase (Per1-luc) reporter rats to monitor molecular clock activity.
• Examined uterine Per1-luc rhythms during non-pregnancy, embryonic day 12 (E12), and E22 under light-dark (LD) and constant darkness (DD) conditions.
• Assessed Per1 mRNA rhythms in placental tissues (decidua and labyrinth) using in situ hybridization.

Main Results:

• The pregnant uterus exhibited clear circadian Per1-luc rhythms, peaking around dusk, irrespective of pregnancy status or light conditions.
• The decidua (maternal placental tissue) displayed circadian Per1 mRNA rhythms, particularly noticeable during nighttime in LD and consistently on E22 in DD.
• The labyrinth (fetal placental tissue) showed no discernible circadian Per1 mRNA rhythms throughout pregnancy in either LD or DD.

Conclusions:

• The maternal uterus and decidua possess functional molecular clocks that can provide circadian information.
• The fetal labyrinth does not exhibit circadian rhythms, indicating it does not contribute to fetal circadian signaling.
• These findings suggest that the maternal reproductive tract, specifically the uterus and decidua, acts as a crucial source of circadian cues for the developing fetus.