Abstract
SummaryLarge-scale phenotyping efforts have demonstrated that approximately 25-30% of mouse gene knockouts cause intra-uterine lethality. Analysis of these mutants has largely focussed on the embryo but not the placenta, despite the critical role of this extra-embryonic organ for developmental progression. Here, we screened 103 embryonic lethal and subviable mouse knockout lines from the Deciphering the Mechanisms of Developmental Disorders programme (https://dmdd.org.uk) for placental phenotypes. 68% of lines that are lethal at or after mid-gestation exhibited placental dys-morphologies. Early lethality (E9.5-E14.5) is almost always associated with severe placental malformations. Placental defects strongly correlate with abnormal brain, heart and vascular development. Analysis of mutant trophoblast stem cells and conditional knockouts suggests primary gene function in trophoblast for a significant number of factors that cause embryonic lethality when ablated. Our data highlight the hugely under-appreciated importance of placental defects in contributing to abnormal embryo development and suggest key molecular nodes governing placentation.
Highlights
Placental defects strongly correlate with abnormal brain, heart and vascular development
Even when including the P14 subviable lines, the placental phenotype rate was still 59%, a far higher frequency than the ~10% annotated in Mouse Genome Informatics (MGI) (Fig. 1b)
When scoring the occurrence of placental defects as a function of developmental stage, we found that almost every line that died before E14.5 exhibited placental abnormalities (40/41; Fig. 1d; Extended Data Fig. 1b), compared to only 35% of lines that were viable beyond E14.5 (12/34) (Fig. 1d; Supplementary Table 1)
Summary
The majority of mouse lines were generated using the EUCOMM/KOMP knockout first conditional-ready targeted ES cell resource (http://www.mousephenotype.org/about-ikmc/ eucomm-program/eucomm-targeting-strategies; targeted trap “tm1a” allele and null “tm1b” allele). All lines were produced and maintained on a C57BL/6N genetic background at the Wellcome Trust Sanger Institute (http://www.mousephenotype.org/) as part of the DMDD project[16]. Use of all animals was in accordance with UK Home Office regulations, the UK Animals (Scientific Procedures) Act of 1986 and approved by the Wellcome Trust Sanger Institute’s Animal Welfare and Ethical Review Body. Corresponding cut-off criteria applied to the designation of sub-viability at E14.5. These “DMDD lines” were assessed at embryonic days E14.5 and/or E9.5, counting the day of the vaginal plug as E0.5. Placentas and yolk sacs were harvested; embryos were processed for HREM imaging[19], placentas were fixed in 4% PFA and yolk sacs were used for genotyping
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