Scientists have identified differences between the male and female brain

Scientists are increasingly recording large-scale differences in gene activity in the brains of men and women. Hundreds of genes in male and female brains show different activity levels, and although the functional significance of these differences remains unclear, some of them are associated with diseases that have a pronounced gender bias - for example, Alzheimer's disease and Parkinson's disease. Studies have also proven that these differences form very early, even at the fetal development stage, and are found in other primates, making them evolutionarily ancient. This is reported by The Conversation portal.

Differences in the structure and function of male and female brains have been documented for several decades. However, until recently, it remained unclear how much they were influenced by environment and learning, and how much by genetic factors. Now this can be investigated directly by analyzing gene activity in different brain tissues using transcriptome analysis. By measuring mRNA levels, scientists can assess which genes are activated or suppressed at the time of research.

The first major comparative analysis of transcriptomes in 2017 showed that about a third of the 20 thousand human genes exhibit sex specificity in activity in at least one type of tissue. The most pronounced differences were found in reproductive organs, but other tissues - including muscles and brain - also show significant shifts. Recent work identified 610 genes that are more active in the male brain, and 316 in the female brain.

Interestingly, the vast majority of such genes are located not on the X or Y chromosomes, but on "regular" autosomes, which are identical in men and women. This means that their activity is regulated by sex-specific signals - for example, hormones. However, some differences emerge too early to be explained by the action of testosterone or estrogen. Analysis of 266 embryonic brains showed that even at the earliest stages of development, more than 1800 genes are more active in boys and about 1300 in girls. This pattern indicates the direct influence of sex chromosome genes on the formation of brain networks long before the appearance of sex glands.

The functional consequences of these differences have only been partially studied so far. The female brain more often shows increased activity of genes related to neuronal function, while male brains show higher activity of genes involved in maintaining membranes, nuclear structures, and other basic processes. Many differences are localized in separate brain regions, which may indicate a specific role in the development of individual cognitive or behavioral functions. However, not all differences in mRNA necessarily lead to differences in protein levels - cells can compensate for changes, maintaining the stability of key networks.

Researchers are particularly interested in the possible connection between sex differences in gene expression and the varying prevalence of neurodegenerative diseases. Many genes associated with Alzheimer's disease are more often active in the female brain, which may partially explain the higher risk in women. In experimental models, it was found that the expression of the male SRY gene in the mouse brain exacerbates the course of Parkinsonism.