A genomic duplication is associated with ectopic eomesodermin expression in the embryonic chicken comb and two duplex-comb phenotypes

PLoS Genet. 2015 Mar 19;11(3):e1004947. doi: 10.1371/journal.pgen.1004947. eCollection 2015 Mar.

Abstract

Duplex-comb (D) is one of three major loci affecting comb morphology in the domestic chicken. Here we show that the two Duplex-comb alleles, V-shaped (D*V) and Buttercup (D*C), are both associated with a 20 Kb tandem duplication containing several conserved putative regulatory elements located 200 Kb upstream of the eomesodermin gene (EOMES). EOMES is a T-box transcription factor that is involved in mesoderm specification during gastrulation. In D*V and D*C chicken embryos we find that EOMES is ectopically expressed in the ectoderm of the comb-developing region as compared to wild-type embryos. The confinement of the ectopic expression of EOMES to the ectoderm is in stark contrast to the causal mechanisms underlying the two other major comb loci in the chicken (Rose-comb and Pea-comb) in which the transcription factors MNR2 and SOX5 are ectopically expressed strictly in the mesenchyme. Interestingly, the causal mutations of all three major comb loci in the chicken are now known to be composed of large-scale structural genomic variants that each result in ectopic expression of transcription factors. The Duplex-comb locus also illustrates the evolution of alleles in domestic animals, which means that alleles evolve by the accumulation of two or more consecutive mutations affecting the phenotype. We do not yet know whether the V-shaped or Buttercup allele correspond to the second mutation that occurred on the haplotype of the original duplication event.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Chick Embryo
  • Chickens / genetics
  • Chickens / growth & development
  • Ectoderm / embryology
  • Ectoderm / growth & development
  • Ectoderm / metabolism
  • Embryonic Development / genetics*
  • Gastrulation / genetics*
  • Gene Expression Regulation, Developmental
  • Genes, Duplicate*
  • Genome
  • Genomics
  • Haplotypes
  • Mutation
  • T-Box Domain Proteins / biosynthesis
  • T-Box Domain Proteins / genetics*

Substances

  • T-Box Domain Proteins

Grants and funding

The work was supported by grants from the ERC project BATESON, the Swedish Research Council Formas, the Swedish Research Council and the Knut and Alice Wallenberg foundation. Sequencing was performed by the SNP&SEQ Technology Platform, supported by Uppsala University and Hospital, SciLife Lab—Uppsala and the Swedish Research Council (80576801 and 70374401). Computer resources were supplied by UPPMAX. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.