In other species: rock pigeon

Categories: Limbs / fins / digit / tail phene

Links to possible relevant human trait(s) and/or gene(s) in OMIM: 119800 (trait) , 186550 (trait) , 602149 (gene)

Mendelian trait/disorder: yes

Disease-related: no

Key variant known: yes

Year key variant first reported: 2020

Species-specific symbol: Pti-2

History: The first published report of this trait was by Hurst (1905). Other early reports were by Davenport (1906, 1909) and Punnett and Bailey (1918).

Inheritance: Up to three separate loci have been postulated to explain the inheritance of this ptilopody, with the trait being due to dominant alleles at two loci and a recessive allele at the third locus; hence the symbols Pti-1, Pti-2 and pti-3 (Somes, 1990; 1992). If more than one locus is confirmed, separate OMIA entries will be created for each locus. At present, the jury is still out. The preceding text was written before 2020. In 2020, the jury (in the form of Li et al. (2020) and Bortoluzzi et al. (2020)) returned its stunning verdict! Pti-1 is the gene TBX5 (OMIA 000839-9031), corresponding to the GGA15 QTL reported by Sun et al. (2015); and Pti-2 is the gene PITX1 (this entry), corresponding to the GGA13 region reported by Dorshorst et al. (2010) and to the GGA13 QTL reported by Sun et al. (2015).

Mapping: Dorshorst et al. (2010) tentatively mapped one ptilopody locus to 15.6Mb on chromosome GGA13. Sun et al. (2015): "Two QTL with 1% genome-wide significant level for feathered feet trait, one 9-cM/2.80-Mb (48.0-57.0/13.40-16.20 Mb) region on GGA13, and another 12-cM/1.45-Mb (41.0−53.0 cM/11.37−12.82 Mb) region on GGA15 were identified". Whole-genome sequencing of a full-sib family in which leg-feathering was segregating enabled Yang et al. (2019) to identify "a total of 24 promising candidate genes potentially affecting feathered-leg trait, i.e. FGF1, FGF4, FGF10, FGFR1, FRZB, WNT1, WNT3A, WNT11, PCDH1, PCDH10, PCDH19, SOX3, BMP2, NOTCH2, TGF-β2, DLX5, REPS2, SCN3B, TCF20, FGF3, FSTL1, WNT7B, ELOVL2 and FGF8." A GWAS conducted by Bortoluzzi et al. (2020) "revealed two significant signals on chromosome 13 and 15". Li et al. (2020) linkage mapped this trait to similar regions on chromosomes 13 and 15.

Molecular basis: In adjacent papers published on the same day in the same journal, Bortoluzzi et al. (2020) and Li et al. (2020) reported that the feathered variant of Pti-2 is a 17.7kb deletion upstream of PITX1. Intriguingly, this deletion is orthologous to the 44kb deletion upstream of PIX1 that gives rise to the same feathered trait in pigeons (see OMIA 002270-8932)

Associated gene: