A domestication related mutation in the thyroid stimulating hormonereceptor gene (TSHR) modulates photoperiodic response andreproduction in chickens

The thyroid stimulating hormone receptor gene (TSHR) has been suggested to be a ‘‘domestication locus”in the chicken. A strong selective sweep over TSHR in domestic breeds together with significant effects ofa mutation in the gene on several domestication related traits, indicate that the gene has been importantfor chicken domestication. TSHR plays a key role in the signal transduction of seasonal reproduction,which is characteristically less strict in domestic animals. We used birds from an advanced intercross linebetween ancestral Red Junglefowl (RJF) and domesticated White Leghorn (WL) to investigate effects ofthe mutation on reproductive traits as well as on TSHB, TSHR, DIO2 and DIO3 gene expression duringaltered day length (photoperiod). We bred chickens homozygous for either the mutation (d/d) or wildtype allele (w/w), allowing assessment of the effect of genotype at this locus while also controlling forbackground variation in the rest of the genome. TSHR gene expression in brain was significantly lowerin both d/d females and males and d/d females showed a faster onset of egg laying at sexual maturity thanw/w. Furthermore, d/d males showed a reduced testicular size response to decreased day length, andlower levels of TSHB and DIO3 expression. Additionally, purebred White Leghorn females kept under naturalshort day length in Sweden during December had active ovaries and lower levels of TSHR and DIO3expression compared to Red Junglefowl females kept under similar conditions. Our study indicates thatthe TSHR mutation affects photoperiodic response in chicken by reducing dependence of seasonal reproduction,a typical domestication feature, and may therefore have been important for chickendomestication.Funding agencies: Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning, FORMAS (Formel Excel); Swedish Research Council, VR; European Research Council (ERC) [322206]