Sex-Specific Abnormalities in Placentae of Conceptuses from DNA-Methyltransferase 1o (Dnmt1o) Deficient Females.

MARTEL, J; FORTIER, A; LANDRY, M; MCGRAW, S; CIRIO, MC; CHAILLET, JR; TRASLER, J

Congreso; Society for the Study of Reproduction (SSR); 2009

The DNA cytosine methyltransferase protein, Dnmt1o, a variantof the larger somatic Dnmt1s methyltransferase is produced inoocytes and present in high concentrations in preimplantationembryos. Dnmt1o, expressed in the nuclei at the 8-cell stage,maintains parental, sex-specific genomic imprints during preimplantationdevelopment. We previously showed that mid-gestation embryosdeveloping in the absence of Dnmt1o have significant delaysin development and a wide range of anatomical abnormalities.The embryos, as well as their placentae, show inappropriatemethylation and variable biallelic expression of imprinted genesat 9.5 dpc. The goal of this study was to further examine theeffect of the Dnmt1o deficiency on extraembryonic tissues. Femalemice lacking oocyte-derived Dnmt1o as well as control femaleswere crossed with wild-type 129/Sv males; embryos and placentaewere collected at 9.5 dpc for gross morphological analysis.Implantation sites were also collected at 9.5 and 10.5 dpc,fixed and subjected to histological analysis. Gross morphologicalassessment was done on 77 placentae from 17 litters (38 femalesand 39 males) of Dnmt1o-deficient females as well as 73 placentaefrom 10 litters (39 females and 34 males) from control females.Extraembryonic hyperplasia was observed in significantly morefemale offspring of Dnmt1o-deficient females than male offspring(47% vs 28%). In both cases, the incidence of extraembryonichyperplasia was greater than for the controls (5% of femaleconceptuses and 12% for males). Further classification of thehyperplastic placentae demonstrated that severe hyperplasiawas more prevalent in the female offspring of Dnmt1o-deficientfemales (24% vs 10% for males); the incidence of severe hyperplasiawas very low in controls (3% for female offspring, 0% for male).Comparison of eosin-hematoxylin stained sections of implantationsites at 9.5 dpc (n=19) and 10.5 dpc (n=32) with controls showedvarying degrees of excessive proliferation of trophoblast giantcells and abnormal branching in the labyrinth despite chorioallantoicattachment occurring in an apparently normal manner. Femaleoffspring displayed the trophoblast giant cell hyperproliferationand aberrant branching phenotypes more frequently than males.Although we did not observe abnormal branching in the controls,we occasionally detected trophoblast giant cell hyperproliferationin these. Further analyses using cell type specific markersare presently underway to further characterize the placentalphenotype. Taken together, these finding indicate that the absenceof the oocyte form of the Dnmt1 protein leads to profound anatomicaland histological abnormalities in the placenta. The increasedincidence of abnormalities in female placenta provides furthersupport for the proposal that the absence of Dnmt1o may alsolead to defects in epigenetic control of genes on the X chromosome.