A frameshift mutation in GON4L is associated with proportionate dwarfism in Fleckvieh cattle

Abstract

Background: Low birth weight and postnatal growth restriction are the most evident symptoms of dwarfism. Accompanying skeletal aberrations may compromise the general condition and locomotion of affected individuals. Several paternal half-sibs with a low birth weight and a small size were born in 2013 in the Fleckvieh cattle population.

Results: Affected calves were strikingly underweight at birth in spite of a normal gestation length and had craniofacial abnormalities such as elongated narrow heads and brachygnathia inferior. In spite of a normal general condition, their growth remained restricted during rearing. We genotyped 27 affected and 10,454 unaffected animals at 44,672 single nucleotide polymorphisms and performed association tests followed by homozygosity mapping, which allowed us to map the locus responsible for growth failure to a 1.85-Mb segment on bovine chromosome 3. Analysis of whole-genome re-sequencing data from one affected and 289 unaffected animals revealed a 1-bp deletion (g.15079217delC, rs723240647) in the coding region of the GON4L gene that segregated with the dwarfism-associated haplotype. We showed that the deletion induces intron retention and premature termination of translation, which can lead to a severely truncated protein that lacks domains that are likely essential to normal protein function. The widespread use of an undetected carrier bull for artificial insemination has resulted in a tenfold increase in the frequency of the deleterious allele in the female population.

Conclusions: A frameshift mutation in GON4L is associated with autosomal recessive proportionate dwarfism in Fleckvieh cattle. The mutation has segregated in the population for more than 50 years without being recognized as a genetic disorder. However, the widespread use of an undetected carrier bull for artificial insemination caused a sudden accumulation of homozygous calves with dwarfism. Our findings provide the basis for genome-based mating strategies to avoid the inadvertent mating of carrier animals and thereby prevent the birth of homozygous calves with impaired growth.

Fig. 1

Phenotypic manifestation of dwarfism in Fleckvieh cattle. a–c A 20-week old Fleckvieh calf with a crooked back, structural abnormalities of the muzzle and brachygnathia inferior. d A 15-month old Fleckvieh bull with dwarfism and a healthy coeval. Note the skin flaps in the neck area. e, f The same animal as in d compared with a 6-month old healthy animal. Note the disproportionately large head of the affected animal (left) (e) although its height (right animal, height at withers: 112 cm) is similar to the nine-month younger healthy animal (left) (f). g An 18-month old animal with dwarfism with excessive skin in the neck area. h The weight of the animal shown in d (blue) is compared to the weight of 74,422 Fleckvieh calves (grey boxes). The upper dotted line represents the growth of Fleckvieh bulls observed in Geuder et al. [46]. The lower dotted line is a growth curve assuming an average weight gain of 1000 g/day, i.e., a lower bound estimate for the growth of Fleckvieh bulls

Fig. 2

Mapping of the genomic region associated with dwarfism. a Association of 787,232 haplotypes with dwarfism in 27 affected and 10,454 unaffected animals. P values were obtained by calculating Fisher exact tests of allelic association. b Autozygosity mapping in 27 animals with dwarfism. Blue and pale blue represent homozygous genotypes (AA and BB), heterozygous genotypes (AB) are displayed in light grey. The solid grey bars represent segments of extended homozygosity in 27 animals with dwarfism. The red bar indicates the shared segment of homozygosity

Fig. 3

A 1-bp deletion in GON4L induces a premature stop codon. a Genomic structure of the bovine Gon-4-like encoding gene GON4L. Grey and light grey boxes represent exons and untranslated regions, respectively. The red triangle represents a 1-bp deletion (rs723240647, g.15079217delC) in exon 20 of GON4L. b The Gon-4-like protein consists of 2239 amino acids and contains highly conserved paired amphipathic helix (PAH) repeat and caspase 8-associated protein 2 myb-like (CASP8AP2) domains. The red star indicates the premature stop codon resulting from the 1-bp deletion

Fig. 4

Retention of intron 20 of the GON4L gene in a Fleckvieh calf with dwarfism. a RT-PCR products were separated by 2 % agarose gel electrophoresis. Lanes 1, 2, and 3 show 348 bp RT-PCR products from lung, lymph nodes, and liver of a wild type animal. Lanes 4, 5, and 6 show 348 and 1488 bp RT-PCR products from lung, lymph nodes, and liver of a homozygous calf. M size marker, N negative RT-PCR control. b Schematic representation of exons 19–22 of wild type GON4L. c Schematic representation of exons 19–22 of the mutant GON4L. Blue arrows represent forward (1F) and reverse primers (1R, 2R). The red ‘X’ displays the premature translation termination at amino acid position 1492 resulting from the retention of intron 20. The light grey colour (c) displays intron 20