MC1R diversity and its role in skin pigmentation variation in West Maharashtra, India

MC1R polymorphisms have been reported to be under a selective constraint in populations inhabiting high UVR regions such as Africans; however, these patterns are not consistent. Here we analyze the MC1R gene in West Maharashtra, India to see if sequence diversity corresponds to their diverse pigmentary profiles and if MC1R is constrained in dark skinned tribal as compared to lighter skinned caste populations.

A 2648 bp region of this gene was sequenced in 102 individuals and the data was compared for π, ϴ diversity indices. Tajima's D was assessed for signatures of purifying selection and MC1R variants were associated with MI measures using the additive, dominant, and recessive models. Pairwise F_ST was tested among study populations and between study populations and 1000 Genomes regional samples.

MC1R diversity was not uniquely patterned among castes and tribes. Non-synonymous variants rs2228479A, rs1805007_T, and rs885479_A showed low variability in these populations. Selection tests did not indicate any constraint on MC1R and pairwise F_ST were also low among the study populations (-0.0163 to 0.06112). The SNP rs3212359 was significantly associated with MI measures when tested using different association models.

We do not find evidence of a selective constraint on MC1R. The presence of a large number of unique haplotypes and low F_ST values at this locus suggests that MC1R polymorphisms may not be influencing pigmentation variation among castes and tribes in this region. Observed associations between rs3212359 and MI measures need to be validated through studies on larger samples and in-vitro functional studies.