A deletion in exon 9 of the LIPH gene is responsible for the rex hair coat phenotype in rabbits (Oryctolagus cuniculus)

Abstract

The fur of common rabbits is constituted of 3 types of hair differing in length and diameter while that of rex animals is essentially made up of amazingly soft down-hair. Rex short hair coat phenotypes in rabbits were shown to be controlled by three distinct loci. We focused on the "r1" mutation which segregates at a simple autosomal-recessive locus in our rabbit strains. A positional candidate gene approach was used to identify the rex gene and the corresponding mutation. The gene was primo-localized within a 40 cM region on rabbit chromosome 14 by genome scanning families of 187 rabbits in an experimental mating scheme. Then, fine mapping refined the region to 0.5 cM (Z = 78) by genotyping an additional 359 offspring for 94 microsatellites present or newly generated within the first defined interval. Comparative mapping pointed out a candidate gene in this 700 kb region, namely LIPH (Lipase Member H). In humans, several mutations in this major gene cause alopecia, hair loss phenotypes. The rabbit gene structure was established and a deletion of a single nucleotide was found in LIPH exon 9 of rex rabbits (1362delA). This mutation results in a frameshift and introduces a premature stop codon potentially shortening the protein by 19 amino acids. The association between this deletion and the rex phenotype was complete, as determined by its presence in our rabbit families and among a panel of 60 rex and its absence in all 60 non-rex rabbits. This strongly suggests that this deletion, in a homozygous state, is responsible for the rex phenotype in rabbits.

Figure 1. The rex hair trait in rabbit.

(A) A normal rabbit coat (A1), a rex rabbit with a castor coat (A2) and an orylag® with a castor coat (A3). (B) Cross section of a fibre bundle of a normal rabbit coat (B1), a rex rabbit (B2) and an orylag® (B3). (C) Skin cross section of a hair follicle group of a normal rabbit coat (C1), a rex rabbit (C2) and an orylag® (C3). Arrows indicate the differences in shape and diameters of primary central hair follicles and their hair.

Figure 2. Distribution of hair diameters in µm (X-axis) in normal (blue) and rex (red) rabbit coats.

Two diameter sizes ranges are represented on two different graphs to cope with the Y-axis scale (frequencies).

Figure 3. Mapping of the rex coat trait in the rabbit families.

A whole genome scan performed on 187 rabbits for 47 microsatellites localized the rex phenotype (INRAR) on rabbit chromosome 14 within an interval of 40 cM. Fine mapping refined the localization within a 0.5 cM (⊖ = 0 ; LOD = 78) region flanked by microsatellites INRA051and INRA086.

Figure 4. LIPH expression in rabbit skin.

LIPH was detected by RT-PCR (ex 7–10) in rabbit skin of 5 common and 5 rex rabbits. The expected product size is 753 pb.

Figure 5. The 1362delA mutation in exon 9 of LIPH in rex rabbits.

(A) Electropherograms of the LIPH exon 9 sequence from a normal common type rabbit (WT), a rex and a heterozygous are shown. The red line indicates the location of the mutation. In heterozygous rabbits there is an overlap of both allele sequences (purple box). (B) Deduced alignment of LIPH proteins between rex and normal common type rabbits. (C) C-terminal conservation in mammalians.