SUMMARYPlacental trophoblasts (TBs) invade and remodel uterine vessels with an arterial bias. This process, which involves vascular mimicry, re-routes maternal blood to the placenta, but fails in pre-eclampsia. We investigated Notch family members in both contexts, as they play important roles in arterial differentiation/function. Immunoanalyses of tissue sections showed step-wise modulation of Notch receptors/ligands during human TB invasion. Inhibition of Notch signaling reduced invasion of cultured human TBs and expression of the arterial marker EFNB2. In mouse placentas, Notch activity was highest in endovascular TBs. Conditional deletion of Notch2, the only receptor upregulated during mouse TB invasion, reduced arterial invasion, the size of maternal blood canals by 30-40% and placental perfusion by 23%. By E11.5, there was litter-wide lethality in proportion to the number of mutant offspring. In pre-eclampsia, expression of the Notch ligand JAG1 was absent in perivascular and endovascular TBs. We conclude that Notch signaling is crucial for TB vascular invasion.

The proteins termed TLE in humans, Grg in mice and Groucho in Drosophila constitute a family of transcriptional corepressors. In mammalians there are five different genes encoding an even larger number of proteins. Interactions between these TLE/Grg proteins and an array of transcription factors has been described. But is there any specificity? This review tries to make a case for a non-redundant function of individual TLE/Grg proteins. The specificity may be brought about by a tightly controlled temporo-spatial expression pattern, post-translational modifications, and subtle structural differences leading to distinct preferences for interacting transcription factors. A confirmation of this concept will ultimately need to come from genetic experiments.

No abstract

Mechanisms of resource allocation are essential for maternal and fetal survival, particularly when the availability of nutrients is limited. We investigated the responses of feto-placental development to maternal chronic protein malnutrition to test the hypothesis that maternal low protein diet produces differential growth restriction of placental and fetal tissues, and adaptive changes in the placenta that may mitigate impacts on fetal growth. C57BL/6J female mice were fed either a low-protein diet (6% protein) or control isocaloric diet (20% protein). On embryonic days E10.5, 17.5 and 18.5 tissue samples were prepared for morphometric, histological and quantitative RT-PCR analyses, which included markers of trophoblast cell subtypes. Potential endocrine adaptations were assessed by the expression of Prolactin-related hormone genes. In the low protein group, placenta weight was significantly lower at E10.5, followed by reduction of maternal weight at E17.5, while the fetuses became significantly lighter no earlier than at E18.5. Fetal head at E18.5 in the low protein group, though smaller than controls, was larger than expected for body size. The relative size and shape of the cranial vault and the flexion of the cranial base was affected by E17.5 and more severely by E18.5. The junctional zone, a placenta layer rich in endocrine and energy storing glycogen cells, was smaller in low protein placentas as well as the expression of Pcdh12, a marker of glycogen trophoblast cells. Placental hormone gene Prl3a1 was altered in response to low protein diet: expression was elevated at E17.5 when fetuses were still growing normally, but dropped sharply by E18.5 in parallel with the slowing of fetal growth. This model suggests that nutrients are preferentially allocated to sustain fetal and brain growth and suggests the placenta as a nutrient sensor in early gestation with a role in mitigating impacts of poor maternal nutrition on fetal growth.

TLE3 is a transcriptional co-repressor that interacts with several DNA-binding repressors, including downstream effectors of the Notch signaling pathway. We generated Tle3-deficient mice and found that they die in utero and their death is associated with abnormal development of the placenta with major defects in the maternal vasculature. In the normal placenta, maternal blood spaces are lined, not as usual in the mammalian circulation by endothelial cells, but rather by specialized embryo-derived cells of the trophoblast cell lineage named trophoblast giant cells (TGC). Tle3 mRNA is expressed in those specialized TGC and Tle3 mutants show severe defects in differentiation of TGC-lined channels and lacunar spaces that take blood out of the labyrinth zone of the placenta and into the uterine veins. The mutants also show somewhat milder defects on the arterial-side of the maternal vascular circuit in spiral arteries and canals that take blood into the labyrinth. Notch2 and Tle3 expression patterns overlap in several TGC subtypes and we found that Tle3 and Notch2 mutants have some overlapping features. However, they also show differences implying that TLE3 may mediate some but not all of the effects of Notch2 signaling during placenta development. Therefore, formation of the different types of maternal blood spaces by different TGC subtypes is regulated by distinct molecular mechanisms.

SUMMARYPancreatic -cells arise from Ngn3 + endocrine progenitors within the trunk epithelium of the embryonic pancreas. The emergence of endocrine cells requires E-cadherin downregulation, but the crucial steps that elicit such are not clear, yet probably important for ultimately being able to efficiently generate -cells de novo from stem cells. Grg3 (groucho-related gene 3, also known as Tle3), encodes a member of the Groucho/TLE family of co-repressors and its function in various cell contexts is mediated by recruitment to target genes by different transcription factors. Grg proteins broadly regulate the progression of progenitor cells to differentiated cell types, but specific developmental mechanisms have not been clear. We find that Grg3 is expressed in most -cells and a subset of other endocrine cell types in the pancreas. Grg3 is highly expressed in Ngn3 + endocrine progenitor descendants just after transient Ngn3 expression. Grg3-null embryos die at E14.5, which is associated with placental defects, so we explanted E12.5 pancreata to allow endocrine differentiation to occur in culture. Grg3 knockout explants displayed a drastic decrease in the differentiation of all endocrine cell types owing to defects in the delamination of early endocrine progenitors from the trunk epithelium. We find that Grg3 normally suppresses E-cadherin gene expression, thereby allowing delamination of endocrine cells from the trunk epithelium and revealing how this transcriptional co-repressor modulates this crucial step of -cell development.

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Development of the mouse embryo to the blastocyst stage occurs over 3 to 4 days following fertilization of the oocyte. During this time, several molecular and morphological events take place that result in the formation of three distinct cell lineages: the trophectoderm, the epiblast, and the primitive endoderm. Many studies have investigated the processes that control lineage specification in the blastocyst including gene expression, cell signaling, cell-cell contact/positional relationships, and most recently, epigenetics. Here we review, at the molecular level, recent contributions to our understanding of the mechanisms that play a role in formation of these lineages. Additionally, we focus on the next steps in differentiation to highlight processes important in the development of those lineages that contribute to the extraembryonic tissues. In this context, we discuss the establishment of extraembryonic ectoderm and the contributions of parietal and visceral endoderm to yolk sac formation.