Identification of genetic components in turkey RyRs associated with PSE meat characteristics

The modern turkey industry has been successful in producing fast-growing birds with large breast muscle due to the application of intensive genetic selection. However, these improvements in growth rate and muscling have led to an increased incidence of pale, soft and exudative (PSE) meat. We hypothesized that (1) polymorphism(s) in the turkey skeletal muscle ryanodine receptor beta isoform (beta-RyR) result in channel activity differences associated with PSE incidence and (2) heat stress affects alternative splicing patterns and abundance of the RyR isoforms (alpha- and beta-RyR) as an adaptive response in some birds, leading to differences in meat quality.; Breast muscle tissues from eighty turkeys from two different genetic lines, i.e., genetically improved and random-bred lines, were obtained after exposure to heat stress for 5 or 7 days. The L* values (objective measurement of lightness of color) and pH at 15 min postmortem of breast muscle were measured. To measure the channel activity of beta-RyR in turkeys, the [3H]-ryanodine binding assay was performed. Ryanodine binding activity of beta-RyR of genetically improved turkeys was significantly increased (p=0.0008) as birds were exposed to longer heat stress while that of random-bred birds was not affected by heat stress level. To test the hypothesis that polymorphisms in beta-RyR are associated with altered channel activity, samples from sixteen turkeys were selected for sequence analysis based on the ryanodine binding activity of beta-RyR. As a result of the screening of the entire beta-RyR cDNA of the selected turkeys, ten synonymous single nucleotide polymorphisms (SNPs) were identified. None of the SNPs showed any significant correlation with ryanodine affinity of beta-RyR. Thus, although the channel activity of ryanodine receptors as measured by [3H]-ryanodine binding assay may suggest a mechanistic basis for differences in calcium fluxes, this assay may not be a good phenotype for identification of polymorphisms of the beta-RyR gene.; To investigate the correlation of those SNPs and meat quality traits, ten normal meat (L*<50 and pH15min>5.8) and ten PSE meat turkeys (L*>52 and pH15min<5.8) were selected based on the L* and pH 15min. Although the SNPs did not change the primary structure of the beta-RyR, four SNPs were associated with color (L*). For those SNPs, heterozygous birds have darker color (L*=49.30) than one type of homozygous birds (L*=53.56) (p<0.01). The pH15min between heterozygous and homozygous turkeys was marginally different (pH15min 6.02, 5.78, respectively; p=0.06). Therefore, there appeared to be an association between the four SNPs and meat quality traits, i.e., the heterozygous turkeys for the mutations show better meat quality than one type of homozygous turkeys.; There was no alternative splicing variant detected in cDNA regions of turkey beta-RyR. Ribonuclease protection assay (RPA) was performed for an alternative splicing region in turkey alpha-RyR to study quantitatively the effect of heat stress level on the pattern and abundance of transcript variants. The assay showed that there are differences in expression pattern of two alternative splicing transcript variants, full-length and AS-81, between random-bred and commercial turkeys exposed to prolonged heat-stress.