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. 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.有假说指出，由于生长策略存在差异，雄性胎仔相较于雌性胎仔对宫内损伤更易感，且胎盘是介导此类性别差异的关键因素。本研究采用四核心基因型（Four Core Genotypes, FCG）小鼠模型，探究了妊娠中期（妊娠第11.5天）开始的母体食物限制（饲喂量为自由采食水平的约60%）对胎仔及胎盘应答的性别差异，同时分析了染色体性别与性腺性别各自的独立作用。食物限制可降低胎仔与胎盘的重量，但对存活孕体的数量无显著影响。然而，食物限制的效应在性腺雄性与性腺雌性孕体之间，或XX与XY型孕体之间均未表现出显著差异。通过RNA测序（RNA sequencing）分析发现，胎盘迷路层以及联合接合带/蜕膜中的基因表达性别差异，完全由染色体性别导致，而非性腺性别。食物限制分别影响了迷路层与联合接合带/蜕膜中的525个和665个基因的表达。但在进行统计交互效应分析时，食物限制的这些效应并未因性腺性别或染色体性别而存在显著差异。与之相反，当单独分析XX型与XY型胎盘时，我们发现了数百个仅在单一性别中受食物限制调控的基因，其中包括数百个在联合分析中未达到显著水平的基因。不过，XX型与XY型胎盘的效应量估计值总体相似，这表明此类按性别分层的分析极大地夸大了性别依赖性应答的程度。总体而言，本研究未发现支持“胎仔生长策略存在性别差异”这一假说的证据，同时发现胎盘基因表达的性别差异主要由染色体性别导致。为探究母体食物限制下胎盘应答的性别差异，我们将C57BL/6J雌性小鼠分别与野生型C57BL/6J雄性小鼠或四核心基因型雄性小鼠交配，后者可产生携带XX雄性、XX雌性、XY雄性及XY雌性的妊娠个体。在妊娠第11.5天时，将单笼饲养的孕鼠随机分配至自由采食对照组，或食物限制组（饲喂量为自由采食水平的约60%）。于妊娠第17.5天采集胎盘并解剖，将迷路层与接合带及蜕膜分离（即接合带与蜕膜合并为一组样本）。本数据集包含迷路层样本。