IDENTIFICATION AND ANALYSIS OF THE DOG KERATIN-9 (KRT9) GENE

We have identified the gene coding for the canine ortholog of the huma n keratin 9 protein using the inverse-polymerase chain reaction (PCR) strategy. Sequence comparison and structure analysis of the gene show marked similarity with the human gene. This gene spans about 7 kb and spreads over eight exons, In the dog gene, the reading frame is extend ed by 20 codons, the first in-frame stop codon being in exon 8 in the dog rather than in exon 7 as in humans. Alignment of human and dog pre dicted amino acid sequences confirms the high analogy, reaching 75% Id entity and 95% similarity in the rod domain. Interestingly, the glycin e-loop motif number in the C-terminal V2 variable subdomain of the pro tein increases from 19 in human to 43 in dog, generating a size differ ence of 12 kDa between the two proteins. Due to its restricted express ion pattern in mammalian epidermis, dog keratin 9 gene was a good cand idate gene for the genetic palmoplantar hyperkeratosis observed in the Dogue de Bordeaux. However, no polymorphism associated with the patho logy was detected within an affected Dogue de Bordeaux pedigree ruling out this hypothesis.