The Strong Selective Sweep Candidate Gene ADRA2C Does Not Explain Domestication Related Changes In The Stress Response Of Chickens

Abstract

Analysis of selective sweeps to pinpoint causative genomic regions involved in chicken domestication has revealed a strong selective sweep on chromosome 4 in layer chickens. The autoregulatory α-adrenergic receptor 2C (ADRA2C) gene is the closest to the selective sweep and was proposed as an important gene in the domestication of layer chickens. The ADRA2C promoter region was also hypermethylated in comparison to the non-selected ancestor of all domesticated chicken breeds, the Red Junglefowl, further supporting its relevance. In mice the receptor is involved in the fight-or-flight response as it modulates epinephrine release from the adrenals. To investigate the involvement of ADRA2C in chicken domestication, we measured gene expression in the adrenals and radiolabeled receptor ligand in three brain regions comparing the domestic White Leghorn strain with the wild ancestor Red Junglefowl. In adrenals ADRA2C was twofold greater expressed than the related receptor gene ADRA2A, indicating that ADRA2C is the predominant modulator of epinephrine release but no strain differences were measured. In hypothalamus and amygdala, regions associated with the stress response, and in striatum, receptor binding pIC50 values ranged between 8.1–8.4, and the level was not influenced by the genotyped allele. Because chicken strains differ in morphology, physiology and behavior, differences attributed to a single gene may be lost in the noise caused by the heterogeneous genetic background. Therefore an F10 advanced intercross strain between White Leghorn and Red Junglefowl was used to investigate effects of ADRA2C alleles on fear related behaviors and fecundity. We did not find compelling genotype effects in open field, tonic immobility, aerial predator, associative learning or fecundity. Therefore we conclude that ADRA2C is probably not involved in the domestication of the stress response in chicken, and the strong selective sweep is probably caused by selection of some unknown genetic element in the vicinity of the gene.

The DomesticBCO2Allele Buffers Low-Carotenoid Diets in Chickens: Possible Fitness Increase Through Species Hybridization

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Selection on the regulation of sympathetic nervous activity in humans and chimpanzees

“…Eleven of them overlapped neuronal DHSs ( S1 Table ). The genomic region spanning the 12 DHSs was similar to the chicken-domestication sweep in size and relative distance to the gene [ 6 ] ( Fig 2A ). Third, we examined histone modification patterns at these 12 DHSs.…”

“…Because there are no other known genes in the identified region, ADRA2C stands out as the most likely candidate. A follow-up study suggests that the target of selection may be noncoding regulatory regions that are distant from the gene body [ 6 ].…”

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“…NE also reduces pain perception [58][59][60][61][62] . ADRα2A, closely associated with pain response, was mutated in Shamo bred for cockfights 63,64 .…”