Genetic and functional evaluation of MITF as a candidate gene for cutaneous melanoma predisposition in pigs

Abstract

Cutaneous melanoma arises from transformed melanocytes and is caused mainly by environmental effects such as ultraviolet radiation and to a lesser extent by predisposing genetic variants. Only a few susceptibility genes for cutaneous melanoma have been identified so far in human; therefore, animal models represent a valuable alternative for genetic studies of this disease. In a previous quantitative trait locus (QTL) study, several susceptibility regions were identified in a swine biomedical model, the MeLiM (Melanoblastoma-bearing Libechov minipig) pigs. This article details the fine-mapping of a QTL located on SSC13 (Sus scrofa chromosome 13) through an increase in marker density. New microsatellites were used to confirm the results of the first analysis, and MITF (microphthalmia-associated transcription factor) was selected as a candidate gene for melanoma development. A single-marker association analysis was performed with single-nucleotide polymorphisms (SNPs) spread over the locus, but it did not reveal a significant association with diverse melanoma-related traits. In parallel, MITF alternative transcripts were characterized and their expression was investigated in different porcine tissues. The obtained results showed a complex transcriptional regulation concordant with the one present in other mammals. Notably, the ratio between MITF+ and MITF- isoforms in melanoma samples followed the same pattern as in human tumors, which highlights the adequacy of the MeLiM pig as a model for human melanoma. In conclusion, although MITF does not seem to be the causal gene of the QTL initially observed, we do not exclude a prominent role of its transcription and function in the outbreak and evolution of the tumors observed in pigs.

Genome‐wide analysis reveals artificial selection on coat colour and reproductive traits in Chinese domestic pigs

“…According to ENSEMBL annotation and reported transcript information (Bourneuf et al . ), none of these variants are located in gene coding regions.…”

“…At the EDNRB and MITF selected regions detected by sequencing, the homozygosity dramatically dropped in all five white-spotted breeds, but no such reduction was observed in solid black Laiwu pigs (Fig. 3b) According to ENSEMBL annotation and reported transcript information (Bourneuf et al 2011), none of these variants are located in gene coding regions.…”

The MeLiM Minipig: An Original Spontaneous Model to Explore Cutaneous Melanoma Genetic Basis

“…The second QTL analysis highlighted a QTL on the swine chromosome 13, directly above MITF locus. However, subsequent studies showed no association between variants in the gene and melanoma phenotypes ( Bourneuf et al, 2011 ). Also, the authors showed that the locus was not amplified in tumor samples, contrary to what is seen in humans.…”

New susceptibility loci for cutaneous melanoma risk and progression revealed using a porcine model

“…In previous studies, the major predisposition genes for human melanoma were discarded: for example, CDKN2A was excluded thanks to an association and a haplotype analysis [ 21 ]. CDK4 alleles did not segregate with melanoma in a reference population [ 19 ], and lastly an association analysis showed that MITF could not be related to melanoma occurrence in the MeLiM model [ 23 ]. This study used the power of a backcross pedigree to identify 21 genomic regions associated with melanoma occurrence and/or progression phenotypes, ie clinical ulceration and presence of local and/or distant metastasis (superficial lymphadenopathy vs visceral metastasis).…”

“…Also, the most significant linkage peak observed in the genome-wide linkage scan was located on SSC13, at about 77Mb according to the version 10.2 of the porcine genome [ 20 ]. The MITF gene was located in this QTL interval, but was discarded as a susceptibility gene, even though its involvement in porcine melanoma tumors makes no doubt [ 23 ]. Although this first attempt to decipher melanoma predisposition in the porcine model yielded interesting results, the experimental design used a low-density marker panel, with an average of one marker every 20cM, thus preventing a fine-mapping of the linked regions.…”