TFAP2 paralogs regulate melanocyte differentiation in parallel with MITF

Abstract

Mutations in the gene encoding transcription factor TFAP2A result in pigmentation anomalies in model organisms and premature hair graying in humans. However, the pleiotropic functions of TFAP2A and its redundantly-acting paralogs have made the precise contribution of TFAP2-type activity to melanocyte differentiation unclear. Defining this contribution may help to explain why TFAP2A expression is reduced in advanced-stage melanoma compared to benign nevi. To identify genes with TFAP2A-dependent expression in melanocytes, we profile zebrafish tissue and mouse melanocytes deficient in Tfap2a, and find that expression of a small subset of genes underlying pigmentation phenotypes is TFAP2A-dependent, including Dct, Mc1r, Mlph, and Pmel. We then conduct TFAP2A ChIP-seq in mouse and human melanocytes and find that a much larger subset of pigmentation genes is associated with active regulatory elements bound by TFAP2A. These elements are also frequently bound by MITF, which is considered the “master regulator” of melanocyte development. For example, the promoter of TRPM1 is bound by both TFAP2A and MITF, and we show that the activity of a minimal TRPM1 promoter is lost upon deletion of the TFAP2A binding sites. However, the expression of Trpm1 is not TFAP2A-dependent, implying that additional TFAP2 paralogs function redundantly to drive melanocyte differentiation, which is consistent with previous results from zebrafish. Paralogs Tfap2a and Tfap2b are both expressed in mouse melanocytes, and we show that mouse embryos with Wnt1-Cre-mediated deletion of Tfap2a and Tfap2b in the neural crest almost completely lack melanocytes but retain neural crest-derived sensory ganglia. These results suggest that TFAP2 paralogs, like MITF, are also necessary for induction of the melanocyte lineage. Finally, we observe a genetic interaction between tfap2a and mitfa in zebrafish, but find that artificially elevating expression of tfap2a does not increase levels of melanin in mitfa hypomorphic or loss-of-function mutants. Collectively, these results show that TFAP2 paralogs, operating alongside lineage-specific transcription factors such as MITF, directly regulate effectors of terminal differentiation in melanocytes. In addition, they suggest that TFAP2A activity, like MITF activity, has the potential to modulate the phenotype of melanoma cells.

Loci associated with skin pigmentation identified in African populations

“…These are in a region with enhancer activity in Europeans (50). For example, SNP rs6497271 (F-test, p-value = 1.8 × 10 −6 ), which is located 437 bp from SNP rs12913832, has been associated with skin color in Europeans (50) and is in a consensus SOX2 motif (a transcription factor which modulates levels of MITF in melanocytes) (57) (Fig. 3).…”

Regulatory Logic Underlying Diversification of the Neural Crest

“…Transcription factor ap2a (Tfap2a) is required for neural crest specification in fish, frog, chick, and mouse [36–39] and has a role in differentiation of melanocytes and sympathetic ganglia (as discussed below) [37,40,41]. In addition, transcription factors Myb, Myc, and Prdm1 are also required for specification [42–44].…”

“…Tfap2a is a pleiotropic transcription factor that has important roles in early neural crest specification as well as many differentiation gene batteries. Recently, Tfap2a will often co-occupy active regulatory elements of melanin synthesis genes with Mitf, including super-enhancers of melanin synthesis genes Dct and Pmel [40]. …”

Discovery of new depigmenting compounds and their efficacy to treat hyperpigmentation: Evidence from in vitro study

“…In general, the medium composition for each culture differs from one to another. Briefly, NHM and NHK were grown in M254, MM4, melanocyte growth medium, Dermal Cell Basal Medium, or MCDB153 . These media contained growth factor which is a vital protein that triggers phosphorylation cascade and stimulates melanoblasts transformation and migration to differentiated functional melanocytes.…”

“…These media contained growth factor which is a vital protein that triggers phosphorylation cascade and stimulates melanoblasts transformation and migration to differentiated functional melanocytes. On the other hand, ETs are important for the adhesion and differentiation of melanocyte, upregulation of MC1R, development of melanocyte dendricity as well as increase MC1R binding activity for α‐MSH, hence increase in TYR activity and TRP1 mRNA expression . Addition of histamine significantly regulates cell proliferation, differentiation, neurotransmission, immunomodulation, dendricity, and TYR protein expression in melanocytes even at a very low dose .…”