Abstract
Impaired migration of primordial germ cells during embryonic development causes hereditary gonadal hypoplasia in both sexes of Northern Finncattle and Swedish Mountain cattle. The affected gonads exhibit a lack of or, in rare cases, a reduced number of germ cells. Most affected animals present left-sided gonadal hypoplasia. However, right-sided and bilateral cases are also found. This type of gonadal hypoplasia prevails in animals with white coat colour. Previous studies indicated that gonadal hypoplasia is inherited in an autosomal recessive fashion with incomplete penetrance. In order to identify genetic regions underlying gonadal hypoplasia, a genome-wide association study (GWAS) and a copy number variation (CNV) analysis were performed with 94 animals, including 21 affected animals, using bovine 777,962 SNP arrays. The GWAS and CNV results revealed two significantly associated regions on bovine chromosomes (BTA) 29 and 6, respectively (P=2.19 x 10-13 and P=5.65 x 10-6). Subsequent cytogenetic and PCR analyses demonstrated that homozygosity of a ~500 kb chromosomal segment translocated from BTA6 to BTA29 (Cs29 allele) is the underlying genetic mechanism responsible for gonadal hypoplasia. The duplicated segment includes the KIT gene that is known to regulate the migration of germ cells and precursors of melanocytes. This duplication is also one of the two translocations associated with colour sidedness in various cattle breeds.
Highlights
Gonadal hypoplasia is characterised by aberrantly small and underdeveloped gonads
We show that Swedish Mountain cattle and Northern Finncattle carry alleles that cause colour-sidedness [15] and that affected individuals are homozygous for the Cs29 allele that includes the ectopic KIT gene
Gonadal hypoplasia in Northern Finncattle and Swedish Mountain cattle is hypothesized to result from pleiotropic effects of a white colour gene because most of the affected animals are predominantly white [6,23]
Summary
Gonadal hypoplasia is characterised by aberrantly small and underdeveloped gonads. Fertility is generally disturbed when both gonads are hypoplastic. Different types of gonadal hypoplasia have been reported in several mammalian species, including cats, dogs [1], sheep [2], horses [3,4] and humans [5]. A few decades later the incidence of gonadal hypoplasia increased heavily and clinical investigations were initiated. Comprehensive health control evaluations were implemented which reduced the incidence of gonadal hypoplasia from 17.3% for Swedish Mountain cattle born before 1937 to 7.3% for animals born between 1952 and 1954 [8]. The Northern Finncattle almost became extinct during the Second World War. considerable introgression of genes from Swedish Mountain cattle took place during the last 65 years and likely introduced gonadal hypoplasia into the Northern Finncattle herd
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