Sandrine Lagarrigue

Messenger RNA levels and transcription rates of hepatic lipogenesis genes in genetically lean and fat chickens

Levels of body fat content in commercial meat chickens have prompted research in order to control the development of this trait. Based on experimentally selected divergent lean and fat lines, many studies have shown that liver metabolism has a major role in the fatness variability. In order to identify which genes are involved in this variability, we investigated the expression of several genes implicated in the hepatic lipid metabolism. The studied genes code for enzymes of fatty acid synthesis [ATP citrate-lyase (ACL), acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), malic enzyme (ME), stearoyl-CoA desaturase (SCD1)], for an apolipoprotein [apolipoprotein A1 (APOA1)], and for the CCAAT/enhancer binding protein α (C/EBPα), which is a transcription factor implied in the regulation of several genes of lipid metabolism. The results show that the fat-line chickens display significantly higher hepatic transcription rates and mRNA levels than the lean-line chickens for the ACL, ME and APOA1 genes. This suggests that these genes could be responsible for the phenotypic fatness variability.

Hepatic lipogenesis gene expression in two experimental egg-laying lines divergently selected on residual food consumption.

Two Rhode Island Red egg-laying lines have been divergently selected on residual food intake (low intake R- line, high intake R+ line) for 19 generations. In addition to direct response, correlated responses have altered several other traits such as carcass adiposity and lipid contents of several tissues, the R+ animals being leaner than the R- ones. In a search for the biological origin of the differences observed in fat deposit, the hepatic mRNA amounts of genes involved in lipid metabolism were investigated. No difference was found between lines for mRNA levels of ATP citrate-lyase, acetyl-CoA carboxylase, fatty acid synthase, malic enzyme and CCAAT/enhancer binding protein α, a transcription factor acting on several lipogenesis genes. The genes coding for stearoyl-CoA desaturase and apolipoprotein A1 displayed significantly lower mRNA levels in the R+ cockerels compared to the R-. All together these mRNA levels explained 40% of the overall variability of abdominal adipose tissue weight, suggesting an important role of both genes in the fatness variability.

Thermal manipulation of the chicken embryo triggers differential gene expression in response to a later heat challenge

BackgroundMeat type chickens have limited capacities to cope with high environmental temperatures, this sometimes leading to mortality on farms and subsequent economic losses. A strategy to alleviate this problem is to enhance adaptive capacities to face heat exposure using thermal manipulation (TM) during embryogenesis. This strategy was shown to improve thermotolerance during their life span. The aim of this study was to determine the effects of TM (39.5xa0°C, 12xa0h/24 vs 37.8xa0°C from d7 to d16 of embryogenesis) and of a subsequent heat challenge (32xa0°C for 5xa0h) applied on d34 on gene expression in the Pectoralis major muscle (PM). A chicken gene expression microarray (8u2009×u200960xa0K) was used to compare muscle gene expression profiles of Control (C characterized by relatively high body temperatures, Tb) and TM chickens (characterized by a relatively low Tb) reared at 21xa0°C and at 32xa0°C (CHC and TMHC, respectively) in a dye-swap design with four comparisons and 8 broilers per treatment. Real-time quantitative PCR (RT-qPCR) was subsequently performed to validate differential expression in each comparison. Gene ontology, clustering and network building strategies were then used to identify pathways affected by TM and heat challenge.ResultsAmong the genes differentially expressed (DE) in the PM (1.5xa0% of total probes), 28 were found to be differentially expressed between C and TM, 128 between CHC and C, and 759 between TMHC and TM. No DE gene was found between TMHC and CHC broilers. The majority of DE genes analyzed by RT-qPCR were validated. In the TM/C comparison, DE genes were involved in energy metabolism and mitochondrial function, cell proliferation, vascularization and muscle growth; when comparing heat-exposed chickens to their own controls, TM broilers developed more specific pathways than C, especially involving genes related to metabolism, stress response, vascularization, anti-apoptotic and epigenetic processes.ConclusionsThis study improved the understanding of the long-term effects of TM on PM muscle. TM broilers displaying low Tb may have lower metabolic intensity in the muscle, resulting in decreased metabolic heat production, whereas modifications in vascularization may enhance heat loss. These specific changes could in part explain the better adaptation of TM broilers to heat.