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Introduction The placenta performs a range of functions to support fetal growth. In addition to facilitating nutrient transport, the placenta also stores glucose as glycogen, which is thought to maintain fetal glucose supply during late gestation. However, evidence to support such a role is currently lacking. Similarly, our understanding of the dynamics of placental glycogen metabolism in normal mouse pregnancy is limited. Methods We quantified the placental glycogen content of wild type C57BL/6JOlaHsd mouse placentas from mid (E12.5) to late (E18.5) gestation, alongside characterising the temporal expression pattern of genes encoding glycogenesis and glycogenolysis pathway enzymes. To assess the potential of the placenta to produce glucose, we investigated the spatiotemporal expression of glucose 6-phosphatase by qPCR and in situ hybridisation. Separate analyses were undertaken for placentas of male and female conceptuses to account for potential sexual dimorphism. Results Placental glycogen stores peak at E15.5, having increased over 5-fold from E12.5, before declining by a similar extent by E18.5. Glycogen stores were 17% higher in male placentas than in females at E15.5. Expression of glycogen branching enzyme (Gbe1) was reduced ~40% towards term. Expression of the glucose 6-phosphatase isoform G6pc3 was enriched in glycogen trophoblast cells and increased towards term. Discussion Reduced expression of Gbe1 suggests a decline in glycogen branching towards term. Expression of G6pc3 by glycogen trophoblasts is consistent with an ability to produce and release glucose from glycogen stores. However, the ultimate destination of the glucose generated from placental glycogen remains to be elucidated.

BAHD1 is a vertebrate protein that promotes heterochromatin formation and gene repression in association with several epigenetic regulators. However, its physiological roles remain unknown. Here, we demonstrate that ablation of the Bahd1 gene results in hypocholesterolemia, hypoglycemia and decreased body fat in mice. It also causes placental growth restriction with a drop of trophoblast glycogen cells, a reduction of fetal weight and a high neonatal mortality rate. By intersecting transcriptome data from murine Bahd1 knockout (KO) placentas at stages E16.5 and E18.5 of gestation, Bahd1-KO embryonic fibroblasts, and human cells stably expressing BAHD1, we also show that changes in BAHD1 levels alter expression of steroid/lipid metabolism genes. Biochemical analysis of the BAHD1-associated multiprotein complex identifies MIER proteins as novel partners of BAHD1 and suggests that BAHD1-MIER interaction forms a hub for histone deacetylases and methyltransferases, chromatin readers and transcription factors. We further show that overexpression of BAHD1 leads to an increase of MIER1 enrichment on the inactive X chromosome (Xi). In addition, BAHD1 and MIER1/3 repress expression of the steroid hormone receptor genes ESR1 and PGR, both playing important roles in placental development and energy metabolism. Moreover, modulation of BAHD1 expression in HEK293 cells triggers epigenetic changes at the ESR1 locus. Together, these results identify BAHD1 as a core component of a chromatin-repressive complex regulating placental morphogenesis and body fat storage and suggest that its dysfunction may contribute to several human diseases., Author Summary The importance of epigenetics in regulation and dysfunction of metabolic pathways is increasingly recognized but the underlying mechanisms and molecular actors involved remain incompletely characterized. Here, we provide evidence that the heterochromatinization factor BAHD1 cooperates with MIER proteins to assemble chromatin-repressive complexes that control a network of metabolic genes involved in placental and fetal growth and in cholesterol homeostasis.

The gap junction gene Connexin31.1 has been reported to be expressed predominantly in the epidermis of murine skin. To study the function of this gene, we generated mice in which the coding DNA of the Connexin31.1 gene was replaced by lacZ reporter coding DNA. Using β-galactosidase staining, we have shown that lacZ/Connexin31.1 was expressed in the spinous and granular layers of the epidermis, in cells of olfactory epithelium and in the vomeronasal organ. During embryogenesis, Connexin31.1 was co-expressed with another isoform, Connexin31, in the post-implantation trophoblast cell lineage and, later in gestation, in placental glycogen cells. Although homozygous Connexin31.1-deficient mice were fertile and showed no morphological or functional defects in adult organs expressing this gene, 30% of the offspring expected according to Mendelian inheritance were lost between embryonic days 11.5 and 14.5 and surviving embryos were significantly reduced in weight near the end of pregnancy. Placentas of Connexin31.1-deficient embryos were reduced in weight and showed altered morphology of the spongiotrophoblast and labyrinth layer. The spongiotrophoblast formed a compact barrier at the decidual border that might restrict the maternal blood supply. We conclude that Connexin31.1 is critical for normal placental development but appears to be functionally compensated by other connexin isoforms in the embryo proper and adult mouse.

Background: Stereology is an established method to extrapolate three-dimensional quantities from two-dimensional images. It was applied to placentation in the mouse, but not yet for other rodents. Herein, we provide the first study on quantitative placental development in a sigmodontine rodent species with relatively similar gestational time. Placental structure was also compared to the mouse, in order to evaluate similarities and differences in developmental patterns at the end of gestation. Methods: Fetal and placental tissues of Necromys lasiurus were collected and weighed at 3 different stages of gestation (early, mid and late gestation) for placental stereology. The total and relative volumes of placenta and of its main layers were investigated. Volume fractions of labyrinth components were quantified by the One Stop method in 31 placentae collected from different individuals, using the Mercator (R) software. Data generated at the end of gestation from N. lasiurus placentae were compared to those of Mus musculus domesticus obtained at the same stage. Results: A significant increase in the total absolute volumes of the placenta and its main layers occurred from early to mid-gestation, followed by a reduction near term, with the labyrinth layer becoming the most prominent area. Moreover, at the end of gestation, the total volume of the mouse placenta was significantly increased compared to that of N. lasiurus although the proportions of the labyrinth layer and junctional zones were similar. Analysis of the volume fractions of the components in the labyrinth indicated a significant increase in fetal vessels and sinusoidal giant cells, a decrease in labyrinthine trophoblast whereas the proportion of maternal blood space remained stable in the course of gestation. On the other hand, in the mouse, volume fractions of fetal vessels and sinusoidal giant cells decreased whereas the volume fraction of labyrinthine trophoblast increased compared to N. lasiurus placenta. Conclusions: Placental development differed between N. lasiurus and M. musculus domesticus. In particular, the low placental efficiency in N. lasiurus seemed to induce morphological optimization of fetomaternal exchanges. In conclusion, despite similar structural aspects of placentation in these species, the quantitative dynamics showed important differences.