Epistatic interactions between at least three loci determine the "rat-tail" phenotype in cattle.

Jacqueline Knaust,Frieder Hadlich,Christa Kuehn,Rosemarie Weikard

doi:10.1186/s12711-016-0199-8

Jacqueline Knaust, Frieder Hadlich + Show 2 more

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https://doi.org/10.1186/s12711-016-0199-8

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Abstract

BackgroundThe “rat-tail” syndrome (RTS) is an inherited hypotrichosis in cattle, which is exclusively expressed in diluted coloured hair. The affected animals also suffer from disturbed thermoregulation, which impairs their health and growth performance. Phenotypic features that are similar to RTS are observed in dogs with black hair follicle dysplasia.ResultsWe used a resource cross population between German Holstein and Charolais cattle breeds to prove that epistatic interactions between at least three independent genetic loci are required for the expression of the RTS phenotype. In this population, the RTS is exclusively expressed in animals with a eumelanic background that is due to the dominant ED allele at the melanocortin 1 receptor gene located on Bos taurus autosome (BTA) 18. In addition, only the individuals that are heterozygous at the dilution locus on BTA5 that corresponds to the premelanosome protein or silver gene variant c.64G>A were classified as displaying a RTS phenotype. Linkage and whole-genome association analyses using different models and different pedigrees allowed us to map a third locus (hereafter referred to as the RTS locus) that is essential for the expression of the RTS phenotype to the chromosomal region between 14 and 22 Mb on BTA5. Our findings clearly demonstrate that the RTS and dilution loci are distinct loci on BTA5.ConclusionsOur study provides evidence that the RTS locus has effects on hair conformation and coat colour dilution and that the effect on coat colour dilution is clearly independent from that of the dilution locus. Finally, our results excluded several other loci that were previously reported to be associated with or to underlie hair conformation or pigmentation traits as the causal mutations of RTS and also several major functional candidate genes that are associated with hypotrichosis in humans. Our finding on the identification of a three-locus interaction that underlies RTS provides a prime example of epistatic interaction between several independent loci that is required for the expression of a distinct phenotype.Electronic supplementary materialThe online version of this article (doi:10.1186/s12711-016-0199-8) contains supplementary material, which is available to authorized users.

Highlights

The “rat-tail” syndrome (RTS) is an inherited hypotrichosis in cattle, which is exclusively expressed in diluted coloured hair
In Holstein and Angus cattle, the black coat colour is caused by the black ED allele at the extension locus that corresponds to the melanocortin 1 receptor (MC1R) gene on Bos taurus autosome (BTA) 18; allele ED is dominant over the E+ wild-type allele and the recessive red e allele [6, 7]
Marron and Beever [12] and Markey [13] postulated that mutations in the hephaestin-like 1 (HEPHL1) gene on BTA29 and the keratin 71 (KRT71) gene on BTA5 are causal for variations in hair structure (HS) that are similar to RTS in Belted Galloway and Hereford, respectively

Summary

Introduction

The “rat-tail” syndrome (RTS) is an inherited hypotrichosis in cattle, which is exclusively expressed in diluted coloured hair. There are several reports on mutations that affect hair length and/or structure in Belted Galloway, Hereford and Fleckvieh cattle. A recent study on the Fleckvieh breed reported a causal mutation in the keratin 27 (KRT27) gene on BTA19 for curly hair [14], which is a phenotype that has been associated with RTS. It should be noted that these mutations affect both pigmented and non-pigmented hair, have no effect on hair length, and/or are present on a pheomelanic phenotypic background. These characteristics are clearly distinct from those of RTS. Because of these partly controversial results, the complete genetic mechanism that underlies RTS is still under debate and our aim was to monitor the genetic architecture of RTS and to map one (or several) locus(i) that are involved in epistatic interaction in a German Holstein × Charolais F2 cross population (i.e. SEGFAM population [15]), segregating for RTS

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