Effects Of Comb Pendulous/upright And RNA-seq Analysis In Rhode Island White Layer

Comb,sexual epidermal appendages on the head,is an important phenotypic trait in chicken.The comb size and colour can be used as an indicator of sexual maturity and production performance.One of attractive comb traits,pendulous comb(PC,comb flops down along one side of the head),is commonly exist in single comb chicken breeds.However,the genetic basis underlying PC still largely unknown.In the present studies,a total of 100 birds(20 roosters and 30 hens for each comb shape,respectively)of D3-line(egg type,300 d)were used to measure the egg number,body weight,body size and comb size.For each comb shape hens,60 eggs were collected for egg quality determination.Moreover,we combined analyzed the concentration of chemical components(e.g.Collagen,hyaluronan and keratan sulfate)and differentially expressed genes in pendulous/upright(PC/UC)comb to reveal the genetic mechanism underlying this phenotype.The results showed that,1)The body weight of roosters with PC was heavier by approximately 6.6% when compared with the UC roosters(P < 0.05).However,there was no significant difference in body weight between hens with two comb shapes(P > 0.05).No significant difference was found of 300 d egg numbers between two comb shapes,in spite of PC hens produced 1.3 eggs more than UC hens.The comb length,height and thickness and body length of PC birds were higher when compered with those of bird with UC(P < 0.05).PC roosters exhibited greater keel length and breast width(P < 0.05),while,UC hens produced darker yolk color eggs(P < 0.05).In addition,the concentration of collagen,hyaluronan and keratan sulfate in UC was higher by 15.4%?29.4% and 16.7% than that of PC.2)The edgeR R package was used to screen for differentially expressed genes(DEGs)between PC and UC.By taking a FDR < 0.05 and |log2(fold change)| > 1 as the cutoff,a total of 31 DEGs were identified.In PC,25 genes were up-regulated and 6 genes were down-regulated when compared with UC.For example,EDN2,FSHR,PSME1,PACAP,SPP1.Enrichment analyzes found that these DEGs enriched in GO terms of the biological process,cellular components and molecular function such as ‘cell part',‘extracellular region',‘developmental process',‘metabolic process',‘signal transducer activity',‘response to stimulus' and ‘immune system process'.Studying by gene function,EDN2 was in connection with collagen synthesis,may lead to PC phenotype in D3-line.