Maternal food-derived signals oscillate in the fetal suprachiasmatic nucleus before its circadian clock develops

The ontogenesis of the circadian clock in the suprachiasmatic nuclei of the hypothalamus (SCN) and its sensitivity to maternal signals are not fully understood. Here, we investigated the development of the clock in the rat SCN from the fetal to the postweaning period and identified rhythmic metabolic signals from the mother to the fetal SCN. We determined daily expression profiles of clock genes (Per2, Nr1d1, Bmal1) and clock- and metabolism-related genes (Dbp, E4bp4) and performed time-resolved analysis of the metabolome and lipidome in the SCN and plasma of 19-day-old embryos (E19) and 2-, 10-, 20-, and 28-day-old pups (P02-28). Our data show that rhythms in the expression of canonical clock genes are absent at E19 and develop gradually until P10, but the Dbp rhythm was still developing between P20 and P28. Expression of the metabolism-sensitive gene E4bp4 and levels of essential amino acids and other metabolites supplied by maternal food are rhythmic in the fetal SCN, which is lost after birth at P02 and reappears later in the postnatal period. Maternal food-derived metabolites were also rhythmic in fetal plasma. The temporal coherence of the fetal SCN metabolome and lipidome declines markedly and its rhythmicity disappears immediately after birth. The results revealed previously unforeseen pathways by which the fetal SCN may receive rhythmic information from the mother before its clock develops.