Bloomsbury report on mouse embryo phenotyping: recommendations from the IMPC workshop on embryonic lethal screening

Abstract

Identifying genes that are important for embryo development is a crucial first step towards understanding their many functions in driving the ordered growth, differentiation and organogenesis of embryos. It can also shed light on the origins of developmental disease and congenital abnormalities. Current international efforts to examine gene function in the mouse provide a unique opportunity to pinpoint genes that are involved in embryogenesis, owing to the emergence of embryonic lethal knockout mutants. Through internationally coordinated efforts, the International Knockout Mouse Consortium (IKMC) has generated a public resource of mouse knockout strains and, in April 2012, the International Mouse Phenotyping Consortium (IMPC), supported by the EU InfraCoMP programme, convened a workshop to discuss developing a phenotyping pipeline for the investigation of embryonic lethal knockout lines. This workshop brought together over 100 scientists, from 13 countries, who are working in the academic and commercial research sectors, including experts and opinion leaders in the fields of embryology, animal imaging, data capture, quality control and annotation, high-throughput mouse production, phenotyping, and reporter gene analysis. This article summarises the outcome of the workshop, including (1) the vital scientific importance of phenotyping embryonic lethal mouse strains for basic and translational research; (2) a common framework to harmonise international efforts within this context; (3) the types of phenotyping that are likely to be most appropriate for systematic use, with a focus on 3D embryo imaging; (4) the importance of centralising data in a standardised form to facilitate data mining; and (5) the development of online tools to allow open access to and dissemination of the phenotyping data.

Fig. 1.

Three-dimensional visualisation of 48 segmented anatomical structures in an E15.5 mouse embryo atlas. Each volume is shown in its native location within the whole mouse embryo volume (semi-transparent). Note that many of the segmented labels cannot be displayed because they are embedded within other structures, especially in the brain.

Fig. 2.

The TCP lethal screen. Outline of the screening procedure of the University of Toronto’s Center for Phenogenomics (TCP) to identify and phenotype recessive embryonic lethal mutants produced from the NORCOMM2 and KOMP2 projects. Heterozygous KO mice (HET) are crossed, the offspring counted on the day of birth (P0), followed by genotyping of 28 surviving pups 2–3 weeks later (P14–P21) to establish the proportion of wild-type (WT), heterozygous mutant and homozygous mutant (HOM) animals produced. If no homozygote mutants are detected despite the absence of any neonatal pup death, the KO is considered embryonic lethal and ∼five litters (28 embryos) are checked for survival of homozygous embryos to the 12th day of gestation (E12.5). Embryos are imaged by μCT on the 15th day of gestation (E15.5) or OPT on the 9th day (E9.5), depending on whether more or less than 50% of the expected mendelian ratio of homozygotes is detected, respectively.

Fig. 3.

Predicted costs associated with embryo phenotyping. Estimated breakdown of the costs associated with phenotyping a single KO strain, based on existing phenotyping programmes and proposals for phenotyping mouse lines from the IMPC and KOMP2 projects.