Roles of chromosomal and gonadal sex in the fetal and placental responses to maternal food restriction in mice

It is hypothesized that male fetuses are more vulnerable to in utero insults than female fetuses due to different growth strategies, and that the placenta contributes to these sex differences. Using the Four Core Genotypes mouse model, we examined sex differences in the fetal and placental responses to maternal food restriction (~60% of ad libitum) beginning mid-gestation (day 11.5), including the independent roles of chromosomal and gonadal sex. Food restriction reduced fetal and placental weights, but had no effect on the number of viable conceptuses. However, the effect of food restriction did not differ between gonadal male and female conceptuses, or between XX and XY conceptuses. Sex differences in gene expression in both the labyrinth and the combined junctional zone/ decidua, as assessed by RNA sequencing, were due entirely to chromosomal sex, and not to gonadal sex. Food restriction affected the expression of 525 and 665 genes in the labyrinth and the combined junctional zone/ decidua, respectively. However, these effects of food restriction did not differ by gonadal sex or chromosomal sex when assessed for statistical interactions. In contrast, when analysing XX and XY placentas separately, we found hundreds of genes that were affected by food restriction in one sex but not the other, including hundreds of genes not found to be significant in the combined analyses. However, estimated effect sizes were generally similar for XX and XY placentas, suggesting that these sex-stratified analyses greatly exaggerated the extent of sex-dependent responses. Overall, we did not find evidence of the hypothesized sex differences in fetal growth strategy, and found that sex differences in placental gene expression were largely due to chromosomal sex. Overall design: To investigate sex differences in the placental response to maternal food restriction, we mated C57BL/6J females with either wildtype C57BL/6J males of Four Core Genotypes (FCG) males, the latter matings producing pregnancies with XX males, XX females, XY males and XY females. On gestational day 11.5, pregnant females were single-housed, and randomly allocated to either the ad libitum diet (control) group, or the food restriction group, which received ~ 60% of ad libitum. At gestational day 17.5, placentas were collected and dissected to separate the labyrinth from the junctional zone and decidua (i.e., junctional zone and decidua were combined). This series includes the labyrinth samples.