Gender influences the risk of disease: this is true for hypertension, diabetes, but also for nervous disorders. Thus, after puberty, women are more affected than men by depression and anxiety. In contrast, boys more often suffer from neurodevelopmental disorders: autism, schizophrenia or attention deficit disorder.
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For the latter, the cause may lie in development in utero. Male embryos are more sensitive to prenatal maternal stress. During embryonic life, the placenta provides the nutrients and growth factors necessary for the development of the fetus. The placenta consists of cells that come from the embryo, which means that genes on the X and Y chromosomes can lead to differences in how the placenta works.
The authors’ approach is rather original since it is oriented towards the placenta. This ephemeral organ is sensitive to changes in the maternal environment: the expression of genes, the morphology of the placenta, its weight, can vary depending on the mother’s diet, her alcohol consumption, her infections or her stress. To better understand the differences between male and female embryos, researchers at the University of Maryland looked at an enzyme that plays a role in placental health: OGT, or O-linked N-acetylglucosamine transferase. OGT acts on the expression profile of genes as a function of sex.
OGT would act through epigenetic modifications called H3K27me3, which correspond – as this abbreviation indicates – to a trimethylation (me3) of lysine 27 (K27) of histone H3. Modification of histones is one of the epigenetic mechanisms influencing gene expression. Patterns of gene expression in the placenta contribute to differences in the development of the hypothalamus, an area often involved in neurodevelopmental disorders, such as autism or schizophrenia.
By maintaining high levels of H3K27me3 in the placenta, the female embryo thus obtains better resistance to maternal stress than male embryos. For Tracy Bale, “this path could help explain why we see this profound neurodevelopmental difference in humans.”
The researcher had already shown that in mice, stress affecting the father could affect the development of the offspring’s brain: stress can alter spermatozoa by epigenetics, which has repercussions on the development of the