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

Dorshorst B, Harun-Or-Rashid M, Bagherpoor AJ, Rubin CJ, Ashwell C, Gourichon D, Tixier-Boichard M, Hallböök F, Andersson L

PLoS Genet. 11 (3) e1004947 [2015-03-00; online 2015-03-19]

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.

NGI Uppsala (SNP&SEQ Technology Platform)

National Genomics Infrastructure

PubMed 25789773

DOI 10.1371/journal.pgen.1004947

Crossref 10.1371/journal.pgen.1004947

pii: PGENETICS-D-14-02046
pmc: PMC4366209