Characterization of a Mouse Model for Bovine Developmental Duplications

Developmental duplications is a genetic condition recently discovered in Angus cattle. It is a congenital abnormality where duplication of neural crest derived tissues occurs during embryonic development. A common phenotypic presentation of the condition includes calves born with polymelia having frequent duplication of the front limbs originating from the neck or shoulder region. Genome-wide association studies have identified a single locus associated with this disease phenotype. Further investigation has indentified the mutation as a nonsynonymous substitution in exon 5 of the NHLRC2 gene. TALENs targeting exon 5 were used for gene-editing of the orthologous locus in mice to further investigate the role of NHLRC2 in development. Three mouse lines were generated having mutations with varying impacts on the NHLRC2 protein. Two mutations (-2 bp and -19 bp) are predicted to cause a prematurely truncated protein and one mutation (-12 bp) the deletion of four amino acids adjacent to the corresponding bovine substitution. Heterozygous mice for each line were mated to phenotypically characterize homozygous progeny. Genotyping of the offspring revealed absence of homozygous individuals suggesting embryonic lethality. Initiation of neural tube closure in mice occurs at day E8.5. Thus, the developmental stage for embryonic death was assessed by harvesting embryos from heterozygous matings at day E8.5 with subsequent genotyping. Yolk sacs containing no embryos were observed, however the number of yolk sacs exceeded the number of live births by 41% (9.5 vs. 6.7), indicating embryonic lethality of homozygous individuals occurs between fertilization and E8.5. Earlier embryonic developmental stages are being analyzed.