In mice, older fathers alter embryo brain genes, differently by sex

In a mouse study, two groups of embryos differ in one way that matters: the age of the father. On one side, embryos conceived by young fathers, 3 months old. On the other, embryos conceived by fathers who were 19 months old. Researchers at Tohoku University looked inside the developing brains of both groups and found that the father's age did not act the same way on males and females.

The team worked on the telencephalon, the part of the embryonic brain that gives rise to structures such as the cerebral cortex. Its cells multiply and specialize very quickly, so a small difference in developmental stage can change which genes are active. The researchers therefore selected embryos whose stage, judged from limb morphology, fell within a window of about four hours. They then read the genetic activity of each brain with RNA sequencing and analyzed males and females separately. Among females, embryos from aged fathers showed a distinct gene expression profile and a tendency toward increased expression levels.

The gap with autism is the heart of the question. ASD is much more common in men than in women, as lead author Noriko Osumi of Tohoku University points out, and research on women has been lacking until now. Studying how biological processes differ by sex is therefore a way to find pathways that a study on one sex alone would miss. The authors are careful, however: their results cannot say whether these sex-dependent differences directly increase the risk of ASD.

What changes, and for whom? For now, mainly for researchers. The full transcriptomic dataset, published in Scientific Data, is a shared resource that other teams can use to examine how paternal aging may shape early brain development in males and females. The next step, according to the team, is to check which genes and gene sets show altered expression and how they may connect to ASD and other conditions, and how these changes might relate to health, behavior and development after birth. Integrating the data with other ASD datasets could help clarify the molecular pathways linking paternal age, brain development and sex differences. No timeline for those results is given. These are mouse results at the stage of gene measurements, and human relevance remains to be established.