Previous research has indicated tightly regulated, even spacing of embryos during implantation is the conserved phenotype seen not only in the mouse and rat but also in other species such as the rabbit, pig, cow, sheep, and human. This critical event is described as embryos spaced evenly along each of the uterine horns of these species, and is an important factor in the health of both the pregnancy and the embryos. For some species this spacing can result in abortion, and in the case of cattle, a condition can occur in response to shared placentas in which sharing of placental vasculature by male-female twins can result in the masculinization of the female fetus. The importance of the proper spacing of embryos has also been suggested from human studies concerning ectopic pregnancies, placental previa, and cases where human fetuses sharing the same placenta are at increased risk of perinatal mortality and morbidity due to twin-twin transfusion syndrome, selective intrauterine growth restriction, and a higher incidence of congenital heart malformations.
The purpose of this study is to determine the genetic factors responsible for the uneven spacing in the C3H mice and its implications. This study utilizes both wild type C3HeB/FeJ (C3H) and C57BL/6J (B6) mice for the purpose of comparison, control, and matings. Wild type C3H mice display reproducibly uneven spacing of their embryos immediately before implantation while wild type B6 mice display the typical phenotype. The use of C3H/B6 recombinant inbred lines will allow us to look at which crosses are affected by uneven spacing and to identify candidate genes responsible for this phenotype through regional origination analysis of each line affected. Regulated contraction of the uterus is suggested to be critical to proper embryo spacing in placental mammals and knockout mice models for Lpar3 and Pla2g4a demonstrated uneven embryo spacing.
Embryo transfers using the parental strains will allow for the determination of message origin, embryo-uterine cross talk, and give insight into the control of embryo spacing in the mouse. RNAseq on uterine tissue and embryos collected from parental strains before implantation will allow us to look at differing expression levels between strains and at the expression levels of potential candidate genes.
Finally, in our wild-type C3H mouse model, we will address the possibility of freemartins occurring in embryos with fused placentas as a result of the uneven spacing. Tattooing techniques will be utilized for identification, postnatal, of pups that share or have fused placentas in utero.