The Evolution of Sex-linked Barring Alleles in Chickens Involves Both Regulatory and Coding Changes in CDKN2A

PLoS Genet. 2017 Apr 7;13(4):e1006665. doi: 10.1371/journal.pgen.1006665. eCollection 2017 Apr.

Abstract

Sex-linked barring is a fascinating plumage pattern in chickens recently shown to be associated with two non-coding and two missense mutations affecting the ARF transcript at the CDKN2A tumor suppressor locus. It however remained a mystery whether all four mutations are indeed causative and how they contribute to the barring phenotype. Here, we show that Sex-linked barring is genetically heterogeneous, and that the mutations form three functionally different variant alleles. The B0 allele carries only the two non-coding changes and is associated with the most dilute barring pattern, whereas the B1 and B2 alleles carry both the two non-coding changes and one each of the two missense mutations causing the Sex-linked barring and Sex-linked dilution phenotypes, respectively. The data are consistent with evolution of alleles where the non-coding changes occurred first followed by the two missense mutations that resulted in a phenotype more appealing to humans. We show that one or both of the non-coding changes are cis-regulatory mutations causing a higher CDKN2A expression, whereas the missense mutations reduce the ability of ARF to interact with MDM2. Caspase assays for all genotypes revealed no apoptotic events and our results are consistent with a recent study indicating that the loss of melanocyte progenitors in Sex-linked barring in chicken is caused by premature differentiation and not apoptosis. Our results show that CDKN2A is a major locus driving the differentiation of avian melanocytes in a temporal and spatial manner.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alleles
  • Animals
  • Cell Differentiation / genetics
  • Chickens
  • Cyclin-Dependent Kinase Inhibitor p16 / genetics*
  • Evolution, Molecular*
  • Feathers / growth & development
  • Feathers / metabolism
  • Female
  • Genetic Linkage*
  • Genotype
  • Mutation
  • Phenotype
  • Pigmentation / genetics*

Substances

  • Cyclin-Dependent Kinase Inhibitor p16

Grant support

This work was supported by the Swedish Research Council (http://www.vr.se) and the Knut and Alice Wallenberg Foundation (https://www.wallenberg.com/kaw/en). DST benefited from an Erasmus-Mundus fellowship and a grant by the Swedish Research Council within the framework of the European Graduate School in Animal Breeding and Genetics (http://www.egsabg.eu/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.