⏰ The impact of the mother's circadian rhythm on the future health of the child

Recent research reveals that a mother's biological clock has an impact on the non-genetic immune variations she transmits to her offspring. This discovery could allow us to better understand why genetically similar individuals exhibit such distinct vulnerabilities to the same pathogens.

This scientific advance sheds light on an unexpected factor of immune diversity. It shows that deep differences in our ability to fight infections are not solely dictated by our DNA or our immediate environment, but could be linked to inherited internal rhythms. To reach these conclusions, researchers conducted experiments on the nematode Caenorhabditis elegans.

A discovery stemming from a model organism

The research team turned to Caenorhabditis elegans, an organism widely studied in biology. Its main advantage lies in the possibility of obtaining genetically identical populations, which allows for the isolation of variations unrelated to heredity. These worms also share fundamental immune pathways with more complex animals, making the observations relevant.

In the laboratory, researchers exposed these worms to the bacterium Pseudomonas aeruginosa. They observed that, despite genetic identity and a rigorously identical environment, the worms showed very disparate immune responses and survival rates when facing infection. This heterogeneity was surprising and indicated a source of variability independent of classic factors.

To identify the origin of these differences, scientists used a fluorescent marker to track the expression of an immune gene, irg-5. They found that individuals with a higher basal level of this biomarker were paradoxically more vulnerable to infections. This simple marker proved to be a reliable predictor of future infection risk.

The central role of the maternal biological clock

The analysis revealed that the variation in the basal level of the immune biomarker was not random. It was directly correlated with the circadian rhythms of each worm's mother. In other words, the mother's internal biological clock influenced the immune "preparedness" of her offspring, establishing a level of risk that persisted throughout its life.

To confirm this link, researchers proceeded with targeted inhibition of the circadian clock regulator genes in the mothers. This manipulation had the effect of completely erasing the differences in vulnerability observed in their offspring. This experiment demonstrated that the maternal circadian rhythm was indeed the primary source of non-genetic immune variability.

The study, published in the journal Science Advances, thus proposes that this transmission of time-related information could be an evolutionary strategy. In a genetically uniform population, this diversity introduced by the maternal clock would increase the chances that at least some individuals would resist an emerging infection, ensuring the survival of the group.

To go further: What is a circadian rhythm?

Circadian rhythms are biological cycles of approximately 24 hours that regulate many functions, from sleep to digestion. They are controlled by a "central clock" in the brain and "peripheral clocks" in the organs. These rhythms are synchronized by environmental signals like light, but continue to function in their absence.

In humans, the disruption of these rhythms, by night work or jet lag, is associated with various health problems. It can disrupt metabolism, cognition and, significantly, the efficiency of the immune system. Studies show that the response to vaccines or the severity of infections can vary depending on the time of day.

These rhythms are therefore much more than a simple sleep clock. They constitute a fundamental temporal regulation system that optimizes the body's functions by anticipating daily cycles. Their role in modulating immune defenses is the subject of a burgeoning field of research, chronoimmunology.