A Genomic Imprinting Defect in Mice Traced to a Single Gene

Abstract

Mammalian androgenones have two paternally or sperm-derived genomes. In mice (Mus musculus) they die at peri-implantation due to the misexpression of imprinted genes-the genes that are expressed monoallelically according to the parent of origin. The misexpressions involved are poorly defined. To gain further insight, we examined the causes of midgestation death of embryos with paternal duplication (PatDp) of distal chromosome 7 (dist7), a region replete with imprinted genes. PatDp(dist7) embryos have a similar phenotype to mice with a knockout of a maternally expressed imprinted gene, Ascl2 [achaete-scute complex homolog-like 2 (Drosophila)], and their death at midgestation could result from two inactive paternal copies of this gene. However, other dist7 misexpressions could duplicate this phenotype, and the potential epistatic load is undefined. We show that an Ascl2 transgene is able to promote the development of PatDp(dist7) embryos to term, providing strong evidence that Ascl2 is the only imprinted gene in the genome for which PatDp results in early embryonic death. While some of the defects in perinatal transgenic PatDp(dist7) fetuses were consistent with known misexpressions of dist7 imprinted genes, the overall phenotype indicates a role for additional undefined misexpressions of imprinted genes. This study provides implications for the human imprinting-related fetal overgrowth disorder, Beckwith-Wiedemann syndrome.

Imprinted genes in mouse placental development and the regulation of fetal energy stores

“…We studied Cdkn1c K/C mutants on a 129S2/SvHsd strain background, and while we also observed profound placental overgrowth, the labyrinth of Cdkn1c mutant placentae was severely disrupted at E18.5 with substantial thrombotic lesions, collagen deposits, impaired vascularisation and a severe S-TGC deficit (Tunster et al 2011). Similar thrombotic lesions were also reported in late-gestation PatUPD7 placentae rescued from lethality by restoration of Ascl2 gene expression (Rentsendorj et al 2010). We also observed a reduced junctional zone at E18.5, which we determined reflected a specific loss of the spongiotrophoblast lineage by marker analysis.…”

Chromosome-Wide Analysis of Parental Allele-Specific Chromatin and DNA Methylation

“…S1 and S3E in the supplemental material). The Ascl2 gene was not interpreted, because an Ascl2 transgene was used to rescue the lethality of PatDup.dist7 MEFs and the hybridization signals may come from the P1 clone integrated elsewhere (78). The other imprinted genes of this domain were not expressed in MatDup.dist7 and PatDup.dist7 MEFs (Th, Tspan32, Kcnq1, and Slc22a18) or were expressed equally in these cells (Cd81, Tssc4, Phld2a, Napl14, Tnfrs23, Osbpl15, and Dhcr7) (see Fig.…”

“…MEFs were derived from 13.5-dpc embryos. PatDup.dist7 embryos that would otherwise die at 10.5 dpc were rescued for this purpose with an Ascl2 transgene (78). The injected P1 clone spanned 84 kb (Fig.…”

“…To assess the chromatin of the parental alleles separately, we used MEFs that carried maternal and paternal duplication of distal Chr7, MatDup.dist7 and PatDup.dist7 (10,11,23,55,78), respectively ( Fig. 1B and C).…”

“…The MatDup.dist7 and PatDup.dist7 genotypes are associated with fetal and embryonic lethality, respectively (10,22,31,55), due to misexpression of imprinted genes. To obtain MEFs at 13.5 days postcoitus (dpc), the PatDup.dist7 embryos had been rescued by an Ascl2 transgene (78,91). MEFs provided a sufficient number of cells for ChIP-on-chip experiments.…”