Influence of X-chromosome dosage on masculine behaviors

Sex differences in the brain and behavior are primarily attributed to dichotomous androgen exposure between males and females during neonatal development, as well as adult responses to gonadal hormones. Here we tested an alternative hypothesis and asked if sex chromosome complement influences male copulatory behavior, a standard behavior for studies of sexual differentiation. We used two mouse models with non-canonical associations between chromosomal and gonadal sex. In both models, we found evidence for sex chromosome complement as an important factor regulating sex differences in the expression of masculine sexual behavior. Counter intuitively, males with two X-chromosomes were faster to ejaculate and display more ejaculations than males with a single X. Moreover, mice of both sexes with two X-chromosomes displayed increased frequencies of mounts and thrusts. It was also discovered that expression of growth hormone in the preoptic area of the hypothalamus and arcuate in the brain correlates with the frequency of male sex behavior and with differences in total body-weight. We speculate that increased expression levels of genes that escape X-inactivation dosage compensation may affect sexual behavior, neural growth hormone expression, and body-weight in mice, and perhaps in other mammals.