Abstract
BackgroundA pig phenotype characterized by juvenile hairlessness, thin skin and age dependent lung emphysema has been discovered in a Danish pig herd. The trait shows autosomal co-dominant inheritance with all three genotypes distinguishable. Since the phenotype shows resemblance to the integrin β6 -/- knockout phenotype seen in mice, the two genes encoding the two subunits of integrin αvβ6, i.e. ITGB6 and ITGAV, were considered candidate genes for this trait.ResultsThe mutated pig phenotype is characterized by hairlessness until puberty, thin skin with few hair follicles and absence of musculi arrectores pili, and at puberty or later localized areas of emphysema are seen in the lungs. Comparative mapping predicted that the porcine ITGB6 andITGAV orthologs map to SSC15. In an experimental family (n = 113), showing segregation of the trait, the candidate region was confirmed by linkage analysis with four microsatellite markers. Mapping of the porcine ITGB6 and ITGAV in the IMpRH radiation hybrid panel confirmed the comparative mapping information. Sequencing of the ITGB6 and ITGAV coding sequences from affected and normal pigs revealed no evidence of a causative mutation, but alternative splicing of the ITGB6 pre-mRNA was detected. For both ITGB6 and ITGAV quantitative PCR revealed no significant difference in the expression levels in normal and affected animals. In a western blot, ITGB6 was detected in lung protein samples of all three genotypes. This result was supported by flow cytometric analyses which showed comparable reactions of kidney cells from affected and normal pigs with an integrin αvβ6 monoclonal antibody. Also, immunohistochemical staining of lung tissue with an integrin β6 antibody showed immunoreaction in both normal and affected pigs.ConclusionA phenotype resembling the integrin β6 -/- knockout phenotype seen in mice has been characterized in the pig. The candidate region on SSC15 has been confirmed by linkage analysis but molecular and functional analyses have excluded that the mutated phenotype is caused by structural mutations in or ablation of any of the two candidate genes.
Highlights
A pig phenotype characterized by juvenile hairlessness, thin skin and age dependent lung emphysema has been discovered in a Danish pig herd
The only not coinciding features are the distribution of the hairlessness and the macrophage and lymphocyte infiltrations observed in the skin and lungs respectively of the knock-out mice
The interstitial pneumonia detected in the lungs of both young and adult pigs is most likely due to infection with porcine circovirus-2 (PCV-2) which is widespread within the Danish population of pigs [19] including our experimental population
Summary
A pig phenotype characterized by juvenile hairlessness, thin skin and age dependent lung emphysema has been discovered in a Danish pig herd. The trait shows autosomal co-dominant inheritance with all three genotypes distinguishable. A phenotype, characterized by juvenile hairlessness, thin skin and age dependent lung emphysema, has been encountered in a Danish pig herd. A similar phenotype has been described in knock-out mice deficient of the ITGB6 gene (ITGB6-/-) encoding the integrin β6-subunit. These mice display juvenile hairlessness mainly on their neck, head and inner thighs, macrophage infiltration of the dermis and lymphocyte infiltration of the conductive airways of the lung. At the age of puberty, hair growth is resumed [1] and later, age dependent lung emphysema appears [2]
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