Sex‐linked barring in chickens is controlled by the CDKN2A /B tumour suppressor locus

Abstract

SummarySex-linked barring, a common plumage colour found in chickens, is characterized by black and white barred feathers. Previous studies have indicated that the white bands are caused by an absence of melanocytes in the feather follicle during the growth of this region. Here, we show that Sex-linked barring is controlled by the CDKN2A ⁄ ⁄ B locus, which encodes the INK4b and ARF transcripts. We identified two non-coding mutations in CDKN2A that showed near complete association with the phenotype. In addition, two missense mutations were identified at highly conserved sites, V9D and R10C, and every bird tested with a confirmed Sex-linked barring phenotype carried one of these missense mutations. Further work is required to determine if one of these or a combined effect of two or more CDKN2A mutations is causing Sex-linked barring. This novel finding provides the first evidence that the tumour suppressor locus CDKN2A ⁄ ⁄ B can affect pigmentation phenotypes and sheds new light on the functional significance of this gene. IntroductionThe diversity of pigmentation in both natural populations and domesticated animals is one of the most studied traits in biology. Pigmentation diversity became a subject for scientific studies in the beginning of the 20th century after the rediscovery of Mendelian genetics (Bateson, 1902;Haldane et al., 1915). Hundreds of genes have been discovered that influence pigmentation in a range of species. In just the mouse, 159 genes affecting pigmentation have been reported (Montoliu et al., 2009). Many of the described causative mutations alter the coding sequence and thus have been straightforward to pinpoint. However, the genetic basis for the bewildering diversity of pigmentation patterns among species, particularly among birds, is poorly understood and is unlikely to be determined by simple loss-of-function mutations. Plumage colour and patterning show great variation among breeds of chickens. To date, five loci controlling SignificanceThe CDKN2A ⁄ B locus has a key role in cell cycle regulation. It encodes both the ARF protein, which binds the p53-stabilizing protein MDM2, and the INK4 protein, a cyclin-dependent kinase inhibitor. Loss-of-function mutations in CDKN2A are responsible for familiar forms of human melanoma. Our study establishes a new animal model for functional studies of CDKN2A because it provides conclusive evidence that mutation(s) in this gene underlies the Sex-linked barring plumage colour in chickens. A barred feather pattern is very common among birds, and to our knowledge, this is the first time that a gene controlling such a pigmentation pattern has been identified.ª

The evolution of Sex-linked barring alleles in chickens involves both regulatory and coding changes in CDKN2A

“…We have previously demonstrated that Sex-linked barring is controlled by dominant alleles at the CDKN2A locus, which encodes the alternate reading frame protein (ARF) [3]. We identified four SNPs located within a 12 kb region including CDKN2A exon 1 (Fig 1B).…”

Topology of Feather Melanocyte Progenitor Niche Allows Complex Pigment Patterns to Emerge

“…2A) is a classical model for pigment patterning (13, 14). This fascinating sex-linked trait is semi-dominant; homozygous males have wider white bands than heterozygous males, and previous work has implicated both coding and non-coding variation at the CDKN2A/B tumor suppressor locus as a potential cause (14). When the growing feather follicle cylinder was cut open vertically from the posterior side, a chevron-shaped barring pattern was revealed (fig.…”

“…The results are consistent with a gain-of-function alteration in the CDKN2A/B tumor suppressor locus that causes premature melanocyte progenitor differentiation in a temporally and topologically restricted manner. The genetic defect in Barred Plymouth Rock chickens may cause aberrant feedback control that displays as repetitive stripes (14, fig. S11).…”

DNA Methylation Analysis of the Gene CDKN2B in Gallus gallus (Chicken)

“…This may be then followed by a new wave of melanocytes recruited from a pool of stem cells, which migrate, colonize the feather follicle, produce melanin and form the next black stripe. Thus, the mutations causing sex-related striation in chickens may have an opposite effect than mutations associated with familiar forms of melanoma in humans (HELLSTRÖM et al 2010).…”

“…As one of the locus bar genes, CDKN2B is responsible for melanin activity in melanocytes (CAMPO 1991: DORSHORST & ASHWELL 2009HELLSTRÖM et al 2010). The present study not only extends the knowledge of the epigenetic regulation of autosexing in Polbar chickens but can also contribute information on neoplastic transformations in human melanocytes.…”