Sex-specific consequences of loss-of-imprinting of the maternally expressed gene Pleckstrin Homology-Like Domain Family A Member 2 (Phlda2) on placental development and fetal growth
TL;DR
A striking biological asymmetry is identified whereby female fetuses reduce their demands on the mother in response to Phlda2 loss-of-imprinting, whereas male fetuses do not, which is linked to sex-specific reproductive strategies in mammals in response to prenatal adversity.
Abstract
Imprinted genes are expressed from one parental allele as a result of epigenetic events initiated in the male and female germlines. We previously identified a role for imprinted genes as master regulators of placental endocrine lineage development in mice. We further reported that loss-of-function of the paternally expressed imprinted gene Peg3 resulted in sexually dimorphic placental and behavioural phenotypes, with the male being relatively more impacted in both cases. Here, we asked whether loss-of-imprinting of the maternally expressed imprinted gene Phlda2 similarly had a sexually dimorphic impact on placental endocrine lineages, potentially underlying male-biased behavioural outcomes that arise when this gene is abnormally expressed. C57BL/6 wildtype (WT) female mice were mated with Phlda2 BACx1 transgenic studs to generate WT control and loss-of-imprinting model samples overexpressing Phlda2 . Placental and fetal weight, placental endocrine lineages and hormone gene expression were characterised at embryonic day (E) 14.5, together with fetal and placenta weight data at E18.5. RNAscope-aided identification of the placental endocrine lineages revealed a significant loss of spongiotrophoblast cells from the junctional zone, with a substantially greater impact on female mutant placenta compared to male. Glycogen cell and parietal trophoblast giant cell number was also diminished but without detectable sexual dimorphism. Reverse-transcription quantitative PCR (RT-qPCR) and RNA sequence analysis supported a female-biased reduction in the expression of placental hormones expressed by the spongiotrophoblast in response to Phlda2 “loss-of-imprinting”. Placental changes were associated with reduced fetal growth in females but not in males late in gestation. Phlda2 expression is known to increase in response to maternal adversity, including nutritional deficiencies, thereby reducing placental “demand” signalling by limiting hormone production. Our new findings identify a striking biological asymmetry whereby female fetuses reduce their demands on the mother in response to Phlda2 loss-of-imprinting, whereas male fetuses do not. Such asymmetries may be linked to sex-specific reproductive strategies in mammals in response to prenatal adversity. Our findings also have implications for human pregnancy research. Elevated placental PHLDA2 has repeatedly been linked to fetal growth restriction and low birthweight but without consideration of the sex of the infant. Our findings that this imprinted gene can exert sex-specific effects on fetal growth may therefore be of translational importance.