Genomic Characterization of the Human Type I Cuticular Hair Keratin hHa2 and Identification of an Adjacent Novel Type I Hair Keratin Gene hHa5

Hair keratins, a subset of the keratin multigene family expressed in hard keratinizing structures, previously have been thought to comprise four members of each subfamily, designated Ha1-4 (type I) and Hb1-4 (type II), which are differentially expressed in the cuticle and cortex of the hair follicle. This report describes the genomic cloning and sequencing of the human type I cuticular hair keratin hHa2, as well as the identification of a previously unknown human type I hair keratin gene. The 12.5-kilobase pair genomic clone ghkI2.12, obtained by hybridization of a human genomic deoxyribonucleic acid library with a 3'–complementary deoxyribonucleic acid probe of hHa2, as well as the partially overlapping 14.4-kilobase pair genornic clone ghk12.17, isolated using a 5'-fragment of clone ghk12.12, allowed the characterization of the entire hHa2 genes The gene displays the same exon/intron structure as two previously characterized type I mouse and sheep hair/wool keratin genes with strict positional conservation of the six introns in the region coding for the central α-helix, At the 5'-extremity of clone ghk12.17, approximately 8.0 kilobase pairs upstream of the hHa2 gene and oriented in the same transcriptional direction, lies the gene for a hitherto unknown human type I hair keratin, Clone ghkl2.17 contains partial sequence information for this gene beginning with introit 5 and extending to the end of the gene. Screening of a human scalp complementary deoxyribonucleic acid library with a 3'-fragment of the gene yielded a full length complementary deoxyribonucleic acid clone of the new hair keratin, which in continuation of the current nomenclature for hair keratins was termed hHa5. Remarkably, the hHa5 gene, which contains an additional 7th intron in its 3'-noncoding region, is expressed mainly in supramatricial cells and lowermost cortical cells of the hair bulb and thus constitutes a very early component of hair morphogenesis. Our results confirm the type specific clustering of keratin genes and indicate that the human type I hair keratin subfamily contains more members than previously assume

The Region Coding for the Helix Termination Motif and the Adjacent Intron 6 of the Human Type I Hair Keratin Gene hHa2 Contains Three Natural, Closely Spaced Polymorphic Sites

Mutations in distinct sites of epidermal keratins, in particular in the helix initiation and termination regions, cause human genodermatoses due to faulty intermediate filament formation. Extension of this observation to human hereditary hair and nail diseases includes population analyses of human hair keratin genes for natural sequence variations in the corresponding sites. Here we report on a large-scale genotyping of the short helix termination region (HTR) of the human type I cortical hair keratins hHa1, a3-I, and a3-II, and the cuticular hair keratin hHa2. We describe two polymorphic loci, P1 and P2, exclusively in the cuticular hHa2 gene, both creating dimorphic protein variants. P1 is due to a C→T mutation in a CpG element leading to a threonine→methionine substitution; P2 concerns a serine codon AGT that also occurs as an asparagine coding variant AAC. A third polymorphism, P3, is linked with a C→T point mutation located at the very beginning of intron 6. The three polymorphic sites are clustered in a 39-nucleotide sequence of the hHa2 gene. Both allelic frequency calculations in individuals of different races and pedigree studies indicate that the two-allelic hHa2 variants resulting from P1 and P2 occur ubiquitously in a ratio of about 1:1 (P1) and 2:1 (P2) respectively in our survey, and are clearly inherited as Mendelian traits. A genotype carrying both mutations simultaneously on one allele could not be detected in our sampling, and there was no association of a distinct allelic hHa2 variant with the known ethnic form variations of hairs. Sequence comparisons of the HTR of hHa2 with those of other type I hair keratins including the hHa2-ortholog from chimpanzee provide evidence that the P1- and P2-linked mutations must have occurred very early in human evolution and that the two P2-associated codon variations may be the result of two independent point mutations in an ancestral AGC serine codon. These data describe natural polymorphisms in the HTR of a member of the keratin multigene family