Caltech researchers have discovered rare types of brain cells that are unique to male mice and others that are unique to female mice. These sex-specific cells were found in a region of the brain that governs both aggression and mating behaviors. The research was published yesterday in Cell.
“The results show that there are differences between male and female mammalian brains at the level of cellular composition as well as gene expression but that those differences are subtle, and their functional significance remains to be explained,” says senior author David Anderson.
There are many different types of cells within the brain, such as neurons that transmit signals and glial cells that support neural functions. Although all of these cells contain the same set of genes, each type of cells differs in how it express those genes.
The hypothalamus is a fundamental region of the brain found in all vertebrates, including humans. Previous studies have shown that a specific anatomic subdivision in the hypothalamus, called the ventrolateral subdivision of the ventromedial hypothalamus (VMHvl), contains cells that control aggression and mating behaviors. In these studies, strong stimulation of these neurons in male and female mice immediately caused the animals to become aggressive, even in the absence of any threat. However, weak stimulation caused the mice to begin mating behaviors.
In the new work, the researchers examined gene expression in individual VMHvl cells using advanced transcriptomic techniques, and they discovered that there are seventeen different types of brain cells in this tiny region alone. What’s more, an examination of the patterns of gene expression revealed that some of these seventeen cell types are much more abundant in males than females, and others are more abundant in females than males.
It was known that different genes are expressed in the two mouse sexes—indeed, a genetic test can tell you whether a mouse is male or female—but this is the first discovery of sex-specific cell types in a mammalian brain. Future work will try to determine the functions of these differing cell types.