<i>Cis</i>-acting mutation affecting <i>GJA5</i> transcription is underlying the <i>Melanotic</i> within-feather pigmentation pattern in chickens.

Abstract

<i>Melanotic</i> (<i>Ml</i>) is a mutation in chickens that extends black (eumelanin) pigmentation in normally brown or red (pheomelanin) areas, thus affecting multiple within-feather patterns [J. W. Moore, J. R. Smyth Jr, <i>J. Hered.</i> 62, 215-219 (1971)]. In the present study, linkage mapping using a back-cross between Dark Cornish (<i>Ml</i>/<i>Ml</i>) and Partridge Plymouth Rock (<i>ml</i>^<i>+</i><i>/ml</i>^<i>+</i> ) chickens assigned <i>Ml</i> to an 820-kb region on chromosome 1. Identity-by-descent mapping, via whole-genome sequencing and diagnostic tests using a diverse set of chickens, refined the localization to the genomic region harboring <i>GJA5</i> encoding gap-junction protein 5 (alias connexin 40) previously associated with pigmentation patterns in zebrafish. An insertion/deletion polymorphism located in the vicinity of the <i>GJA5</i> promoter region was identified as the candidate causal mutation. Four different <i>GJA5</i> transcripts were found to be expressed in feather follicles and at least two showed differential expression between genotypes. The results showed that <i>Melanotic</i> constitutes a <i>cis</i>-acting regulatory mutation affecting <i>GJA5</i> expression. A recent study established the <i>melanocortin-1 receptor</i> (<i>MC1R)</i> locus and the interaction between the MC1R receptor and its antagonist agouti-signaling protein as the primary mechanism underlying variation in within-feather pigmentation patterns in chickens. The present study advances understanding the mechanisms underlying variation in plumage color in birds because it demonstrates that the activity of <i>connexin 40/GJA5</i> can modulate the periodic pigmentation patterns within individual feathers.