Figure 1. The Naked neck phenotype is caused by a cis-regulatory mutation that results in elevated BMP12 expression.

(A) Adult Na/Na. Feathers are absent on the neck and head, excepting the crown. (B) E8.5 embryos hybridized with a β-catenin probe to mark the patterning field and feather primordia. Punctate expression of β-catenin in feather placodes is seen on the body but not the neck of the mutant. WT, wild type; Na/Na, Naked neck. (C) E12.5 embryos showing limited lateral tract expansion (arrows) in Na/Na, reducing body feather coverage. (D) Quantitative RT-PCR determination of BMP12 expression in body and neck skin of E7.5 and E8.5 wild type and Na/Na embryos. (E,F) In situ hybridization detecting BMP12 in wild type and Na/Na embryos at (E) E7.5 and (F) E8.5. Wild type and mutant embryos were hybridized and photographed together. Na/Na embryos have elevated and diffuse expression of BMP12 in the skin. (G) Sequence traces of PCR products from E8.5 Na/+. Genomic DNA PCR products display double peaks following a TA indel polymorphism in the BMP12 3′UTR. RT-PCR products from neck and body skin show a single trace throughout, indicating predominant expression of the Naked neck BMP12 allele, while both alleles are detected in RT-PCR products from other tissues. (H) Schematic showing insertion of chromosome 1 sequences into chromosome 3 at the Naked neck locus. Chromosome coordinates, the Naked neck identical by descent segment, gene names, exons, untranslated regions, and non-coding elements conserved between chicken and human genomes, based on the ENSEMBL genome viewer, are indicated.