Influences of Reduced Expression of Maternal Bone Morphogenetic Protein 2 on Mouse Embryonic Development

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Abstract
Bone morphogenetic protein 2 (BMP2) was originally found by its osteoinductive ability, and recent genetic analyses have revealed that it plays critical roles during early embryogenesis, cardiogenesis, decidualization as well as skeletogenesis. In the course of evaluation of the conditional allele for Bmp2, we found that the presence of a neo cassette, a selection marker needed for gene targeting events in embryonic stem cells, in the 3′ untranslated region of exon 3 of Bmp2, reduced the expression levels of Bmp2 both in embryonic and maternal mouse tissues. Some of the embryos that were genotyped as transheterozygous for the floxed allele with the neo cassette over the conventional null allele (fn/–) showed a lethal phenotype including defects in cephalic neural tube closure and ventral abdominal wall closure. The number of embryos exhibiting these abnormalities was increased when, due to different genotypes, expression levels of Bmp2 in maternal tissues were lower. These results suggest that the expression levels of Bmp2 in both embryonic and maternal tissues influence the normal neural tube closure and body wall closure with different thresholds.