Balanced translocations for the analysis of imprinted regions of the mouse genome

miR-126 regulates glycogen trophoblast proliferation and DNA methylation in the murine placenta

A functional placenta develops through a delicate interplay of its vascular and trophoblast compartments. We have identified a previously unknown expression domain for the endothelial-specific microRNA miR-126 in trophoblasts of murine and human placentas. Here, we determine the role of miR-126 in placental development using a mouse model with a targeted deletion of miR-126. In addition to vascular defects observed only in the embryo, loss of miR-126 function in the placenta leads to junctional zone hyperplasia at E15.5 at the expense of the labyrinth, reduced placental volume for nutrient exchange and intra-uterine growth restriction of the embryos. Junctional zone hyperplasia results from increased numbers of proliferating glycogen trophoblast (GlyT) progenitors at E13.5 that give rise to an expanded glycogen trophoblast population at E15.5. Transcriptomic profile of miR-126^-/- placentas revealed dysregulation of a large number of GlyT (Prl6a1, Prl7c1, Pcdh12) and trophoblast-specific genes (Tpbpa, Tpbpb, Prld1) and genes with known roles in placental development. We show that miR-126^-/- placentas, but not miR-126^-/- embryos, display aberrant expression of imprinted genes with important roles in glycogen trophoblasts and junctional zone development, including Igf2, H19, Cdkn1c and Phlda2, during mid-gestation. We also show that miR126^-/- placentas display global hypermethylation, including at several imprint control centers. Our findings uncover a novel role for miR-126 in regulating extra-embryonic energy stores, expression of imprinted genes and DNA methylation in the placenta.

Uniparental disomy and human disease: an overview

Uniparental disomy (UPD) refers to the situation in which both homologues of a chromosomal region/segment have originated from only one parent. This can involve the entire chromosome or only a small segment. As a consequence of UPD, or uniparental duplication/deficiency of part of a chromosome, there are two types of developmental risk: aberrant dosage of genes regulated by genomic imprinting and homozygosity of a recessive mutation. UPD models generated by reciprocal and Robertsonian translocation heterozygote intercrosses have been a powerful tool to investigate genomic imprinting in mice, whereas novel UPD patients such as those with cystic fibrosis and Prader-Willi syndrome, triggered the clarification of recessive diseases and genomic imprinting disorders in human. Newly developed genomic technologies as well as conventional microsatellite marker methods have been contributing to the functional and mechanistic investigation of UPD, leading to not only the acquisition of clinically valuable information, but also the further clarification of diverse genetic processes and disease pathogenesis.

Analysis of mouse conceptuses with uniparental duplication/deficiency for distal chromosome 12: comparison with chromosome 12 uniparental disomy and implications for genomic imprinting

Distal mouse chromosome 12 is imprinted. Phenotypic analysis of mouse embryos with maternal or paternal uniparental disomy for the whole of chromosome 12 has characterized the developmental defects associated with the altered dosage of imprinted genes on this chromosome. Here we conduct a characterization of maternal and paternal Dp(dist12) mice using the reciprocal translocation T(4;12)47H. This limits the region analysed to the chromosomal domain distal to the T47H breakpoint in B3 on mouse chromosome 12. Both MatDp(dist12)T47H and PatDp(dist12)T47H conceptuses are non-viable and the frequency of recovery of Dp(dist12) conceptuses by 10.5 days post coitum (dpc) was lower than expected after normal adjacent-1 disjunction. A subset of MatDp(dist12) embryos can survive up to one day post partum. In contrast to paternal uniparental disomy 12 embryos, no live PatDp (dist12) embryos were recovered after 16.5 days of gestation. Other phenotypes observed in maternal and paternal chromosome 12 uniparental disomy mice are recapitulated in the Dp(dist12) mice and include placental, muscle and skeletal defects. Additional defects were also noted in the skin of both MatDp(dist12) and maternal uniparental disomy 12 embryos. This study shows that the developmental abnormalities associated with the altered parent of origin for mouse chromosome 12 can be attributed to the genomic region distal to the T47H breakpoint.