| Polydactyly(Po) is a kind of breed identity in chicken, Which is a common limb defect in vertebrates. Through comparative genomics research, it was found there is a homologous gene and similar mechanism underlying polydactyly among different species. Lmbrl is the candidate gene for PPD in human and mouse, It should be the candidate gene for chicken polydactyly.The coding sequence (CDS) of chicken Lmbrl was cloned and an short splicing form of chicken Lmbrl transcripts was detected which is the result of the complete deletion of exon 4 as C7orf2 in human Acheiropodia (ACHP). In addition, six cSNPs were detected in the CDS of chicken Lmbrl by RT-PCR from five-toed Silkies and four-toed White Plymouth Rock broilers. Two of them were missense mutation, and four for silence mutation. A797G and T1254C polymorphisms show the tendency of special change between silikies and White Plymouth Rock broilers on RNA level.The 10-16 introns of chicken Lmbrl were cloned and found their splicing sites follow the consensus (5'AG/N, 3'N/GT). The size of chicken part Lmbrl genomic gene including 10-17 exons is about one fifth to the corresponding region of human C7orf2 and one third to the corresponding region of mouse Lmbrl. We predict the whole genomic size of chicken Lmbrl is about 50-60kb. Through sequencing, 63 SNPs in the introns of chicken Lmbrl were detected. The ratio of transition and transversion is 1.6:1.Po also behaves as an incomplete dominant in CAU resource reference population established by silkies and White Plymouth Rock broilers. We first reported that T1254C in the coding sequence of chicken Lmbrl is the special mutation site for polydactyly in CAU resource population.Homologous TT for T1254C corresponds to polydactyly, homoogous CC for T1254C corresponds to normal, heterozygote for T1254C corresponds to polydactyly or normal, the penetrance of the Polydactyly in heterozygote for T1254C is 84%. T1254C poymorphism could expain the phenotype variation in digit number,which shows that T1254C has a critical role for polydactyly.In our research, we observed clear association between PCR-SSCP genotypes and breeds (or digit phenotype) in Parents population by three pairs of primers. Silkies have special haplotype in intron 13 and exon 16.Our research showed that the mutations of Lmbrl also have a significant association with some carcass characters .The association analysis on PCR-SSCP genotype related with T1254C polymorphism and carcass characters shows ,the eviscerated yield rate for AA genotype was 62.93%,which was significant lower than that of BB genotype (63.83%) (P<0.05),while the gizzard rate for/L4 genotype was 2.21% ,which was significant higher than that of BB genotype (2.00%) (P<0.05); the shank girth for AA genotype was 4.31cm ,which was significant higher than that of AB genotype(4.17cm) and extremely significant higher than that of BB genotype (4.11cm) (PO.OJ );The shank and claw rate for AA genotype was 6.43% ,which was extremely significant higher than that of BB genotype (5.97%) .Combining with T1254C and G1255A polymorphisms, we also observed an extremely significant association between genotype and the shank and claw rate and shank girth(P<0.01).The close association of chicken Lmbrlpolymorphism with digit phenotype and the shank and claw rate demonstrates that Lmbrl gene has multi-effect or is extremely linked with main QTL for these carcass traiteJLmbr] is the key gene for controling polydactyly in chicken. The close association of chicken Lmbrl gene polymorphism with the shank and claw rate and shank girth also gives us a hint that Lmbrl gene may have an important role not only on polydactyly but also on skeleton development.The chicken Lmbrl gene was mapped to chromosome 2p region near ADL0270 by linkage analysis and RH mapping method(cR=30.6,Lod=8.23), this region is the homology with human 7q36 and mouse 5B1 chromosome including C7orf2/Lmbrl where localized the preaxial polydactyly(PPD) mutant in mouse and human. The mapping results and functional analysis demonstrate that Lmbrl...
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