Male and female brains are different in important ways — not just in generating distinct sexual behaviours, but also in terms of cognition and other key functions. Until recently, these differences were thought to arise from the effects of sex hormones during brain development, but there have been several hints lately that genes in the adult brain have a role in maintaining this male–female divide. Work from Eric Vilain and colleagues now shows that the Y-chromosome gene Sry directly influences the function of the brain in adult males.

Sry is a transcriptional regulator and is best known as the master controller of male sexual development. However, previous studies have shown that, intriguingly, this gene is also expressed in the adult male brain. Vilain and colleagues confirmed this, showing that Sry mRNA is present at a low level throughout the brain cortex in male mice, and at higher levels in two regions: the mammillary bodies and the substantia nigra (SN). Focusing on the SN, which controls voluntary movement, the authors showed that the SRY protein colocalizes with tyrosine hydroxylase (TH), an enzyme that is involved in the synthesis of the neurotransmitter dopamine, which is essential for the functioning of this region.

To investigate the functions of SRY in TH-expressing cells, male rat SNs were microinfused with antisense oligonucleotides targeted against Sry. This led to reduced TH expression in the SN and in regions that are usually innervated by TH-expressing neurons, showing that SRY directly regulates the expression of this enzyme. The authors were also able to show that SRY expression in the SN has a functional consequence. Microinfusion of Sry antisense oligonucleotides into the SN on one side of the brain reduced the stepping activity of rats using the forelimb on the corresponding side of the body.

The fact that SRY functions in the adult male brain in a way that doesn't rely on hormones indicates that we should think differently about sexual dimorphisms in the brain, taking direct genetic effects into account. This will be important for many reasons, not least for understanding the differing susceptibilities of men and women to psychiatric disorders and other neurological diseases.