Identification of a nonsense mutation in FGF20 in scaleless. (A) Sequence traces from WT, sc/+ and sc/sc individuals covering c.526 to c.543 of FGF20, showing the open reading frame, c.535A > T mutation in sc/sc and corresponding p.R179X in the predicted protein sequence. (B) Schematic of the chicken FGF20 protein. Pink bars indicate predicted receptor interaction sites and blue bars indicate HSPG binding motifs (information obtained from NCBI Domains, accessed 17/8/11: http://www.ncbi.nlm.nih.gov/Structure/cdd/wrpsb.cgi). The p.R179X mutation is predicted to cause loss of receptor and HSPG binding sites. (C) Multiple sequence alignment of vertebrate FGF20 sequences to amino acids 170 to 207 of chicken FGF20. The position of the premature termination caused by the scaleless mutation in chicken FGF20 is indicated above the alignment. Sequence divergence is illustrated by shading of amino acids. The residues downstream of chicken FGF20 R179 are highly conserved across species.