Identification of regulatory genes for tenderness and lipogenesis by transcriptomic and proteomic approach in beef cattle fed with different diets

Abstract

Brazil plays an enormous and important role in the world beef market and considering the increasing number of animals finished in feedlots further studies on meat quality traits are needed. In feedlots, diets with a high proportion of starch (e 70%) may be used. Alternatively, in order to reduce the costs of the formulations, the reduction of the corn grain (and starch) is possible through the use of co-products such as distillers grains (WDG). However, the impacts of starch reduction by the use of WDG on intramuscular lipogenesis and meat quality traits are unknown, especially in crossbred cattle. In this context, the objectives of the project are to study the effects of reducing starch ratios in the finishing diet by including WDG on lipid metabolism and meat quality characteristics (tenderness, marbling and color aspect) of crossbred cattle, as well the association of the phenotypes with the proteome and transcriptome of the muscle tissue. The experimental trial will be the same as the project approved in FAPESP (process 2016/04478-0), in which will be used 100 male not castrated F1 Angus-Nellore. The animals will be submitted to a finishing diet containing WDG in four levels of inclusion (0, 15, 30 and 45%). After slaughter, longissimus thoracis (LT) muscle samples will be collected and evaluated for quality traits. LT muscle aliquots will be collected immediately at slaughter and stored in liquid nitrogen for subsequent molecular study. We will measure Shear force (SF), cooking loss (CL), backfat thickness (BFT), rib eye area (REA), myofibrillar proteolysis (MFI), visual marbling index (IM), lightness (L*), Chroma (saturation) and Hue (actual color) in LT samples. The molecular approach will use a pool of LT muscle samples from animals fed with control (n = 25) versus those fed with WDG (15, 30 e 45%) (n = 25 each). In these animals, proteomic studies using two-dimensional electrophoresis and mass spectrometry will be conducted. The LT muscle transcriptome from the same animals will be investigated by RNA-Seq technique. In addition, the higher inclusion of WDG coupled with the reduction of the starch ratio may lead to a change in the deposition of intramuscular fat and other characteristics, an effect that may be associated with the role of central proteins of the lipid metabolism. There are no studies in the literature that investigated such hypotheses in crossbred F1 Angus-Nellore cattle, highlighting the importance of the current proposal. In addition, the relationships between the variables SF, CL, BFT, REA, MFI, IM, lightness, Chroma, Hue, proteins, and genes will be studied by principal component analysis, non-hierarchical clustering (K-means) and discriminant analysis. There are few studies with a multivariate approach to meat quality and molecular biology data. It is fundamental to improve characteristics of economic importance for industry and consumers, aiming also the use of this information in breeding programs and nutrigenomics studies. The subject is current and relevant in genetics and animal breeding, which will be studied by an innovative methodological approach that look forward to relate phenotypic characteristics to cellular processes at their molecular level.