Copy number expansion of the STX17 duplication in melanoma tissue from Grey horses

Abstract

BackgroundGreying with age in horses is an autosomal dominant trait, associated with loss of hair pigmentation, melanoma and vitiligo-like depigmentation. We recently identified a 4.6 kb duplication in STX17 to be associated with the phenotype. The aims of this study were to investigate if the duplication in Grey horses shows copy number variation and to exclude that any other polymorphism is uniquely associated with the Grey mutation.ResultsWe found little evidence for copy number expansion of the duplicated sequence in blood DNA from Grey horses. In contrast, clear evidence for copy number expansions was indicated in five out of eight tested melanoma tissues or melanoma cell lines. A tendency of a higher copy number in aggressive tumours was also found. Massively parallel resequencing of the ~350 kb Grey haplotype did not reveal any additional mutations perfectly associated with the phenotype, confirming the duplication as the true causative mutation. We identified three SNP alleles that were present in a subset of Grey haplotypes within the 350 kb region that shows complete linkage disequilibrium with the causative mutation. Thus, these three nucleotide substitutions must have occurred subsequent to the duplication, consistent with our interpretation that the Grey mutation arose more than 2,000 years before present.ConclusionsThese results suggest that the mutation acts as a melanoma-driving regulatory element. The elucidation of the mechanistic features of the duplication will be of considerable interest for the characterization of these horse melanomas as well as for the field of human melanoma research.

Regulatory mutations in TBX3 disrupt asymmetric hair pigmentation that underlies Dun camouflage color in horses

“…NimbleGen Sequence Capture Arrays (Roche NimbleGen) were designed to target the 200-kb region on horse chromosome 8 harboring the Dun locus. Targeted resequencing was performed as described 25 . Subsequent to the discovery of the non-dun2 deletion, sequence for the deletion was obtained via Sanger sequencing for these seven individuals.…”

Complex Inheritance of Melanoma and Pigmentation of Coat and Skin in Grey Horses

“…Examination of melanoma tissue revealed copy number variation of the 4.6 kb intron in STX17, with a difference between blood and tumor DNA. The highest copy numbers occurred in tumors classified as aggressive [10]. Grey horses are the only animals to present progressive coat greying, melanoma, vitiligo-like skin depigmentation and coat speckling, making them an excellent model for studying the inheritance of traits with complex genetic background.…”

Ectopic differentiation of melanocyte stem cells is influenced by genetic background

“…For instance, age‐related graying in horses is attributed to an intronic duplication in the syntaxin‐17 gene, yet Connemara horses gray much later than horses of other breeds carrying the same mutation. This suggests that the presence of modifier genes in the Connemara breed provides resistance to this phenotype (Rosengren Pielberg et al., ; Sundström et al., ). As a second example, ionizing radiation (IR) causes hair graying in mice, and susceptibility to IR varies by genetic background; strong F mice show increased depletion of follicular melanocytes after IR in comparison with DBA/1 and C57BL/6 mice (Potten, ).…”