ABOVE: While still in utero, rat pups pick up on their mother’s metabolic rhythms, which are orchestrated by a molecular clock in her brain and synched to her feeding patterns. © iStock.com, Kseniia Glazkova

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Within the hypothalamus, dual structures called the suprachiasmatic nuclei (SCN) act as a central clock for the circadian system, setting daily rhythms that in mature individuals are largely coordinated by genes known as clock genes. This clock doesn’t fully mature in mammals until after birth, but despite this, previous studies have noted early signs of circadian rhythms in the SCN of gestating rat pups. 

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Physiologist Alena Sumová of the Czech Academy of Sciences in Prague wanted to understand what was driving these early signals, so her team designed an experiment using pregnant rats kept in constant darkness. Rats in one group had functioning SCN and were fed a standard diet ad libitum, while the other group had their SCN surgically removed but were fed on a strict schedule. 

Transcriptomics and proteomics revealed daily rhythmicity in genes that are expressed in the pups’ SCN, including genes that are functionally linked to brain development and cell-cell signaling, in both groups. When the mother’s SCN are intact, they contribute to these expression patterns in the pups even in the absence of light or feeding cues. When the mothers lack SCN, a strict feeding schedule still seems to create its own metabolic rhythm that triggers daily cycles in pups, says Urs Albrecht, a biochemist at the University of Fribourg in Switzerland who was not involved in the work. “Due to that rhythmic metabolism, the pups get information in a metabolic manner . . . which then induces a rhythmicity of gene expression,” he tells The Scientist.

Sumová notes that although the data come from animal research, “they underscore the importance of a regular daily regime” during pregnancy, as the disruption or absence of circadian signaling has been linked to premature births and other poor health outcomes.

P. Greiner et al., “Early rhythmicity in the fetal suprachiasmatic nuclei in response to maternal signals detected by omics approach,” PLOS Biol, 20:e3001637, 2022.