A Novel Mutation in the Maternally Imprinted PEG3 Domain Results in a Loss of MIMT1 Expression and Causes Abortions and Stillbirths in Cattle (Bos taurus)

Congenital malformations resulting in late abortions and stillbirths affect the economic wellbeing of producers and the welfare of cattle in breeding programs. An extremely high incidence of stillbirths of "half-sized" calves of normal karyotype and uninflated lungs was diagnosed in the progeny of the Finnish Ayrshire (Bos taurus) bull--YN51. No other visible anatomical abnormalities were apparent in the stillborn calves. We herein describe the positional identification of a 110 kb microdeletion in the maternally imprinted PEG3 domain that results in a loss of paternal MIMT1 expression and causes late term abortion and stillbirth in cattle. Using the BovineSNP50 BeadChip we performed a genome-wide half-sib linkage analysis that identified a 13.3 Mb associated region on BTA18 containing the maternally imprinted PEG3 domain. Within this cluster we found a 110 kb microdeletion that removes a part of the non-protein coding MER1 repeat containing imprinted transcript 1 gene (MIMT1). To confirm the elimination of gene expression in calves inheriting this deletion, we examined the mRNA levels of the three maternally imprinted genes within the PEG3 domain, in brain and cotyledon tissue collected from eight fetuses sired by the proband. None of the fetuses that inherited the microdeletion expressed MIMT1 in either tissue. The mutation, when inherited from the sire, is semi-lethal for his progeny with an observed mortality rate of 85%. The survival of 15% is presumably due to the incomplete silencing of maternally inherited MIMT1 alleles. We designed a PCR-based assay to confirm the existence of the microdeletion in the MIMT1 region that can be used to assist cattle breeders in preventing the stillbirths.