Liver and muscle metabolic changes induced by dietary energy content and genetic selection in rainbow trout (Oncorhynchus mykiss)

We combined genetic selection and dietary treatment to produce a model to study metabolic pathways involved in genetic and nutritional control of fat deposition in fish muscle. Two experimental lines of rainbow trout, selected for a lean (L) or fat (F) muscle, were fed with diets containing either 10 or 23% lipids from the first feeding, up to 6 mo. At the end of the feeding trial, trout were distinguished by very different muscle fat content (from 4.2 to 10% wet weight), and line x diet interactions were observed for parameters related to fat storage. We analyzed the activity and gene expression of key enzymes involved in lipid metabolism (fatty acid synthase, hydroxyacyl-CoA dehydrogenase, carnitine palmitoyltransferase 1 isoforms, and peroxisome proliferator-activated receptor alpha) and glycolysis (hexokinase 1 and pyruvate kinase) as well as energy production (isocitrate dehydrogenase, citrate synthase, and cytochrome oxidase) in the liver and the white muscle of rainbow trout. The lipid-rich diet repressed the activity of the lipogenic enzymes and stimulated enzymes involved in fatty acid oxidation and glycolysis in liver but had little effect on muscle enzymes assessed in this study. Regarding the selection effect, enzyme activity and expression suggest that compared with the L line, the F line presented reduced hepatic fatty acid oxidation as well as reduced mitochondrial oxidative capacities and enhanced glucose utilization in both liver and muscle. Very few line x diet interactions were found, suggesting that the two factors (i.e., dietary energy content and selection) used in this study to modify muscle lipid content exerted some additive but mostly independent effects on these metabolic actors.     

The ability of genetically lean or fat slow-growing chickens to synthesize and store lipids is not altered by the dietary energy source

The increasing use of unconventional feedstuffs in chicken’s diets results in the substitution of starch by lipids as the main dietary energy source. To evaluate the responses of genetically fat or lean chickens to these diets, males of two experimental lines divergently selected for abdominal fat content were fed isocaloric, isonitrogenous diets with either high lipid (80 g/kg), high fiber (64 g/kg) contents (HL), or low lipid (20 g/kg), low fiber (21 g/kg) contents (LL) from 22 to 63 days of age. The diet had no effect on growth performance and did not affect body composition evaluated at 63 days of age. Glycolytic and oxidative energy metabolisms in the liver and glycogen storage in liver and Sartorius muscle at 63 days of age were greater in chicken fed LL diet compared with chicken fed HL diet. In Pectoralis major (PM) muscle, energy metabolisms and glycogen content were not different between diets. There were no dietary-associated differences in lipid contents of the liver, muscles and abdominal fat. However, the percentages of saturated (SFA) and monounsaturated fatty acids (MUFA) in tissue lipids were generally higher, whereas percentages of polyunsaturated fatty acids (PUFA) were lower for diet LL than for diet HL. The fat line had a greater feed intake and average daily gain, but gain to feed ratio was lower in that line compared with the lean line. Fat chickens were heavier than lean chickens at 63 days of age. Their carcass fatness was higher and their muscle yield was lower than those of lean chickens. The oxidative enzyme activities in the liver were lower in the fat line than in the lean line, but line did not affect energy metabolism in muscles. The hepatic glycogen content was not different between lines, whereas glycogen content and glycolytic potential were higher in the PM muscle of fat chickens compared with lean chickens. Lipid contents in the liver, muscles and abdominal fat did not differ between lines, but fat chickens stored less MUFA and more PUFA in abdominal fat and muscles than lean chickens. Except for the fatty acid composition of liver and abdominal fat, no interaction between line and diet was observed. In conclusion, the amount of lipids stored in muscles and fatty tissues by lean or fat chickens did not depend on the dietary energy source.     

Liver metabolism traits in two rabbit lines divergently selected for intramuscular fat

Intramuscular fat (IMF) has a large effect in the sensory properties of meat because it affects tenderness, juiciness and flavour. A divergent selection experiment for IMF in longissimus dorsi (LD) muscle was performed in rabbits. Since liver is the major site of lipogenesis in rabbits, the objective of this work is to study the liver metabolism in the lines of the divergent selection experiment. Intramuscular fat content, perirenal fat weight, liver weight, liver lipogenic activities and plasma metabolites related to liver metabolism were measured in the eighth generation of selection. Direct response on IMF was 0.34 g/100 g of LD, which represented 2.7 SD of the trait, and selection showed a positive correlated response in the perirenal fat weight. High-IMF line showed greater liver size and greater liver lipogenic activities of enzymes glucose-6-phosphate dehydrogenase and malic enzyme. We did not find differences between lines for fatty acid synthase lipogenic activity. With regard to plasma metabolites, low-IMF line showed greater plasma concentration of triglycerides, cholesterol, bilirubin and alkaline phosphatase than high-IMF line, whereas high-IMF line showed greater albumin and alanine transaminase concentrations than low-IMF line. We did not observe differences between lines for glucose, total protein and plasma concentrations. Phenotypic correlations between fat (IMF and perirenal fat weight) and liver traits showed that liver lipogenesis affects fat deposition in both, muscle and carcass. However, the mechanisms whereby liver lipogenesis affected IMF content remain to be clarified.     

Plasma lipoprotein metabolism in lean and in fat chickens produced by divergent selection for plasma very low density lipoprotein concentration

Plasma lipoprotein metabolism was studied in vivo in two lines of chickens produced by selection for high and low plasma very low density lipoprotein (VLDL) concentration. Rates of VLDL secretion were measured by determining the rate of accumulation of triglyceride in the plasma after intravenous injection of anti-lipoprotein lipase antibody. The clearance of VLDL-triglyceride and its uptake into liver and adipose tissue was examined using radioactively labeled VLDL synthesized in vivo. The rate of VLDL secretion was about threefold higher in the high-VLDL line as compared to the leaner, low VLDL-line (6.7 vs 2.1 mumol VLDL triglyceride/h per ml of plasma). The clearance of VLDL from the circulation of the low VLDL line was much faster than that of the high VLDL line (t1/2 of 3.7 and 13.6 min, respectively). The proportion of administered radiolabel taken up by the abdominal fat pad was substantially greater in the fat line than in the lean line (11.9 vs 4.8%, respectively). Lipoprotein lipase activities in leg muscle and heart were consistently greater in the low-VLDL line and beta-hydroxybutyrate concentrations in the plasma of the low-VLDL line were significantly greater than those in the high-VLDL line (0.86 vs 0.48 mumol/ml). The results show that the approximately tenfold difference in plasma VLDL concentration between lines is primarily due to markedly different rates of hepatic VLDL production and that selection has made a major effect on partitioning of VLDL triglyceride between adipose and other tissues.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of Glucose and Lipid Metabolic Gene Expressions between Fat and Lean Lines of Rainbow Trout after a Glucose Load

Two experimental rainbow trout lines developed through divergent selection for low (Lean ‘L’ line) or high (Fat ‘F’ line) muscle fat content were used as models to study the genetic determinism of fat depots. Previous nutritional studies suggested that the F line had a better capability to use glucose than the L line during feeding trials. Based on that, we put forward the hypothesis that F line has a greater metabolic ability to clear a glucose load effectively, compared to L line. In order to test this hypothesis, 250 mg/kg glucose was intraperitoneally injected to the two rainbow trout lines fasted for 48 h. Hyperglycemia was observed after glucose treatment in both lines without affecting the phosphorylation of AMPK (cellular energy sensor) and Akt-TOR (insulin signaling) components. Liver glucokinase and glucose-6-phosphate dehydrogenase expression levels were increased by glucose, whereas mRNA levels of β-oxidation enzymes (CPT1a, CPT1b, HOAD and ACO) were down-regulated in the white skeletal muscle of both lines. Regarding the genotype effect, concordant with normoglycemia at 12 h after glucose treatment, higher muscle glycogen was found in F line compared to L line which exhibited hyperglycemia. Moreover, mRNA levels of hepatic glycolytic enzymes (GK, 6PFK and PK), gluconeogenic enzyme PEPCK and muscle fatty acid oxidation enzymes (CPT1a, CPT1b and HOAD) were concurrently higher in the F line. Overall, these findings suggest that F line may have a better ability to maintain glucose homeostasis than L line.     

Growth and body composition changes in mice selected for high post-weaning weight gain on two levels of feeding

Summary Two lines of mice were selected for high post-weaning weight gain (3 to 6 weeks) adjusted for 3 week weight. One line (F) was grown on freely available food and the other (S) on a feeding scale set at the same level for all mice. Food intake of the S line averaged 80% of the F line. The realised heritabilities after 6 generations of selection were 0.38±0.06 and 0.33±0.07 for the F and S lines, respectively. In generation 7, mice from the F and S lines and from an unselected control line (C) were compared on both free and set levels of feeding from 3 weeks to 9 weeks of age. Measurements taken were growth rate, appetite, food conversion efficiency (weight gain/food intake) and body composition (fat, protein, ash, water). The F and S lines grew more rapidly and efficiently than the C line on both levels of feeding, each line performing best on the level of feeding on which it was selected. The average genetic correlation between growth rates of the same line on the two feeding levels was 0.54±0.10. The F line grew 19% faster and was 9% more efficient than the S line on free feeding but the S line grew 15% faster and was 15% more efficient than the F line on set feeding. Relative to the C line, food intake per day on free feeding was 4% higher in the F line and 6% lower in the S line. There was no difference between the lines in food intake/g body weight. The rate of deposition of all body components increased in both selection lines. In the F, S and C lines respectively, efficiencies of gains in body components (10²x gain/food) were 1.79, 1.31 and 1.06 for fat, 1.53, 1.63 and 1.22 for protein and 5.88, 6.45 and 4.98 for protein + water. Apparently energy lost as heat was reduced in both the F and S lines. The partitioning of energy retained was altered in favour of more fat in the F line and more protein in the S line.     

A comprehensive analysis of QTL for abdominal fat and breast muscle weights on chicken chromosome 5 using a multivariate approach

Quantitative trait loci (QTL) influencing the weight of abdominal fat (AF) and of breast muscle (BM) were detected on chicken chromosome 5 (GGA5) using two successive F₂ crosses between two divergently selected 'Fat' and 'Lean' INRA broiler lines. Based on these results, the aim of the present study was to identify the number, location and effects of these putative QTL by performing multitrait and multi-QTL analyses of the whole available data set. Data concerned 1186 F₂ offspring produced by 10 F₁ sires and 85 F₁ dams. AF and BM traits were measured on F₂ animals at slaughter, at 8 (first cross) or 9 (second cross) weeks of age. The F₀, F₁ and F₂ birds were genotyped for 11 microsatellite markers evenly spaced along GGA5. Before QTL detection, phenotypes were adjusted for the fixed effects of sex, F₂ design, hatching group within the design, and for body weight as a covariable. Univariate analyses confirmed the QTL segregation for AF and BM on GGA5 in male offspring, but not in female offspring. Analyses of male offspring data using multitrait and linked-QTL models led us to conclude the presence of two QTL on the distal part of GGA5, each controlling one trait. Linked QTL models were applied after correction of phenotypic values for the effects of these distal QTL. Several QTL for AF and BM were then discovered in the central region of GGA5, splitting one large QTL region for AF into several distinct QTL. Neither the 'Fat' nor the 'Lean' line appeared to be fixed for any QTL genotype. These results have important implications for prospective fine mapping studies and for the identification of underlying genes and causal mutations.     

Changes in the body composition of mice selected for high and low eight week weight

Summary Body composition was studied in three lines of mice, one selected for high (H) and one for low (L) 8 week weight, and one maintained as an unselected control (C). After 25 generations 8 week weights were 41.2g, 30.6 g and 20.5g for the H, C and L lines. Mice were sampled from the lines and analysed for fat, protein, ash and water at generations 14 and 25. Apart from fat in the H line, there was little alteration due to selection in the relationships between individual body components and total body weight. In the H line, the contribution of fat to body weight gain was considerably increased. Although leaner than the C and L mice at low body weights, H line mice rapidly became fatter with increasing body weight. Selection appeared to reduce the body weight at which fat was deposited at its maximum rate in the H line. The H and C lines were equally fat at body weights of 29.0 g and 21.6 g at generations 14 and 25 respectively. Body weights at points of inflection of the growth curves of the H, C and L lines at generation 25 were 18.3 g, 14.3 g and 12.8 g. The implications of these findings for meat species slaughtered at set weights are discussed.     

Correlated response in body condition and energy mobilisation in rabbits selected for litter size variability

A divergent selection experiment on litter size variability (high and low lines) was performed in rabbits over seven generations. The aim of this study was to evaluate the correlated responses to selection in body condition and fat reserves mobilisation. Litter size variability was estimated as phenotypic variance of litter size within female after correcting for the year-season and the parity-lactation status effects. A total of 226 females were used in this study, of which 158 females were used to measure body condition and energy mobilisation. Body condition was measured as BW and perirenal fat thickness. Females were stimulated with the adrenergic isoproterenol. Mobilisation capacity of fat reserves was measured by the lipolytic potential, defined as the increment in non-esterified fatty acids (NEFA) levels from basal concentration until adrenergic stimulation at mating, delivery and 10 days after delivery of the second reproductive cycle. Females were classified as survivor or non-survivor when they were culled for sanitary reasons or died before the third kindling. Data were analysed using Bayesian methodology. Survivor females presented higher BW than the non-survivor females at delivery (238 g, P=1.00) and 10 days after delivery (276 g, P=1.00). They also showed higher perirenal fat thickness at 10 days after delivery (0.62 mm, P=1.00). At delivery, basal NEFA levels was lower in survivor than non-survivor females (−0.18 mmol/l, P=1.00), but their lipolytic potential (∆NEFA) was higher (0.08 mmol/l, P=0.94). Body weight was similar between lines in survivor females. Perirenal fat thickness was lower in the high line than in the low line at delivery (−0.23 mm, P=0.90) and 10 days after delivery (−0.28 mm, P=0.92). The high line exhibited higher NEFA (0.10 mmol/l, P=0.93) and lower ∆NEFA (−0.08 mmol/l, P=0.92) than the low line at delivery. The low line showed a favourable correlated response to selection on body condition and fat reserves mobilisation. In conclusion, the low line selected for litter size variability seems to adapt better to adverse conditions, as it has a greater capacity to mobilise energy reserves at delivery than the high line. Females that adequately manage their body reserves and perform energy mobilisation correctly have a lower risk of dying or being culled.     

Leptin levels in lines of mice developed by long-term divergent selection on fat content

The mouse lines were developed by long-term selection for fatness, after which the fat line (F) had about a 5-fold (23% vs 4%) higher fat percentage than the lean (L) line at 14 weeks; but the lines differed little in fat-free body weight. To assess the contribution of genetic changes in leptin hormone level to the selection response, plasma leptin levels were assayed in these lines in generation 60 and in an unselected control (C) from the same base population. With access to food prior to assay, the F, C and L lines had 16.5, 0.91 and 0.26 ng/ml leptin, respectively. In fasted animals these levels were much lower: 2.98, 0.171 and 0.0087 ng/ml, respectively. Thus the leptin levels differ greatly between the lines, with the fattest mice showing the highest level: almost 20 times higher than the control and 60-300 times higher than the L line. These correlated selection effects are an order of magnitude greater than the direct selection response, and believed to be much larger than seen for any hormonal or other trait. Correlations between leptin level and fat amount were high (over 0.86) in fed or fasted animals of the F line, indicative of leptin resistance.     

MUC1 gene polymorphism in three Nelore lines selected for growth and its association with growth and carcass traits

The objective of this study was to describe the VNTR polymorphism of the mucin 1 gene (MUC1) in three Nelore lines selected for yearling weight to determine whether allele and genotype frequencies of this polymorphism were affected by selection for growth. In addition, the effects of the polymorphism on growth and carcass traits were evaluated. Birth, weaning and yearling weights, rump height, Longissimus muscle area, backfat thickness, and rump fat thickness, were analyzed. A total of 295 Nelore heifers from the Beef Cattle Research Center, Instituto de Zootecnia de Sert?ozinho, were used, including 41 of the control line, 102 of the selection line and 152 of the traditional. The selection and traditional lines comprise animals selected for higher yearling weight, whereas control line animals are selected for yearling weight close to the average. Five alleles were identified, with allele 1 being the most frequent in the three lines, especially in the lines selected for higher means for yearling weight. Heterozygosity was significantly higher in the control line. Association analyses showed significant effects of allele 1 on birth weight and weaning weight while the allele 3 exert significant effects on yearling weight and back fat thickness. Despite these findings, application of this marker to marker-assisted selection requires more consistent results based on the genotyping of a larger number of animals in order to increase the accuracy of the statistical analyses.     

鸡瘦蛋白受体(OBR)基因内含子8单核苷酸多态性与体脂性状的相关研究

以东北农业大学高低脂双向选择系的第 6世代肉鸡为材料 ,鸡 7周龄时测定体重和腹脂重等屠体性状。根据鸡瘦蛋白受体基因内含子 8的序列 (GenBank登陆号 :AF2 2 2 783 )设计引物 ,用直接测序的方法检测多态性位点 ,用PCR SSCP的方法进行基因型分析 ,建立适合的统计模型对多态性位点产生的基因型与生长和体组成性状进行相关分析。结果表明 ,在第 50 0和 659位碱基同时发生了T—C、G—A突变。经最小二乘分析 ,3种基因型在腹脂重和腹脂率上差异显著 (P <0 0 5) ,BB型个体腹脂重和腹脂率显著高于AB型 (P <0 0 5) ,极显著地高于AA型个体 (P <0 0 1) ;3种基因型在肝重上差异显著 (P <0 0 5) ,且AA基因型个体的肝重显著低于AB和BB基因型个体。初步推断OBR基因可能是影响鸡脂肪性状的主效基因或与主效基因连锁 ,推测可以利用这个多态位点对鸡的体脂性状进行标记辅助选择     

Phenotypic characterisation of extreme growth-selected mouse lines: An important prerequisite for future QTL analysis

A unique set of seven mouse lines, long-term selected for high growth, from different laboratories around the world has been comprehensively compared to evaluate these resources for future QTL and gene mapping for growth traits. The heaviest line (DUH) was 40% (males) to 44% (females) heavier than the smallest line (ROH) at birth, and 105% (males) to 114% (females) heavier at 98 d. Body conformation (body length and width, body areas), body composition (dry matter, fat, fatty acid composition, organ weights), and skeletal muscle cellularity also differed substantially. DUH was more than 20% longer (12.3 cm) compared to the shortest line ROH (9.7 cm). DAH (22.5%) had the highest percentage of gonadal fat and the leanest was BEH (7.7%). Line BEH (0.49 g) showed the highest weight for the left M. rectus femoris, which was 2.1 times higher, compared to ROH (0.23 g). These results suggest that different alleles, and possibly different physiological pathways, have contributed to the selection response in the different lines. Therefore these selection lines are an important tool with which to identify the genetic and physiological basis of growth as they may contain many, if not all, growth promoting alleles.     

Identification of quantitative trait loci influencing traits related to energy balance in selection and inbred lines of mice.

Energy balance is a complex trait with relevance to the study of human obesity and maintenance energy requirements of livestock. The objective of this study was to identify, using unique mouse models, quantitative trait loci (QTL) influencing traits that contribute to variation in energy balance. Two F2 resource populations were created from lines of mice differing in heat loss measured by direct calorimetry as an indicator of energy expenditure. The HB F2 resource population originated from a cross between a noninbred line selected for high heat loss and an inbred line with low heat loss. Evidence for significant QTL influencing heat loss was found on chromosomes 1, 2, 3, and 7. Significant QTL influencing body weight and percentage gonadal fat, brown fat, liver, and heart were also identified. The LH F2 resource population originated from noninbred lines of mice that had undergone divergent selection for heat loss. Chromosomes 1 and 3 were evaluated. The QTL for heat loss identified on chromosome 1 in the HB population was confirmed in the LH population, although the effect was smaller. The presence of a QTL influencing 6-wk weight was also confirmed. Suggestive evidence for additional QTL influencing heat loss, percentage subcutaneous fat, and percentage heart was found for chromosome 1.     

Evaluation of TFAM and FABP4 gene polymorphisms in three lines of Nellore cattle selected for growth

We analyzed the polymorphisms TFAM HaeIII, TFAM MboI and FABP4 MspA1I in three Nellore lines selected for growth in order to evaluate how selection affects the frequencies of these polymorphisms and evaluate their association with growth and carcass traits in Zebu cattle. Birth, weaning and yearling weights, rump height, longissimus muscle area, backfat thickness, and rump fat thickness were analyzed. The sample was constituted of animals from two lines selected for yearling weight (NeS and NeT), and a control line (NeC), established in 1980, at the S?o Paulo Instituto de Zootecnia. Two hundred and seventy-two heifers were genotyped for TFAM gene SNPs, and 325 heifers were genotyped for the FABP4 SNP. High frequencies were observed for the alleles A (TFAM HaeIII), C (TFAM MboI) and C (FABP4 MspA1I). Significant differences in allele frequencies between NeS and NeT were observed for the TFAM HaeIII, and between the line NeT and lines NeC and NeS for the FABP4 MspA1I SNP. Five haplotypes were observed for the two polymorphisms in the TFAM gene, haplotype AACC being the most frequent. None of the markers separately or according to haplotype was significantly associated with the growth and carcass traits. The low frequencies of alleles that are associated with high marbling scores and thick subcutaneous fat in taurine breeds might explain the low means for these traits in Nellore cattle.     

Genetic selection, sex and feeding treatment affect the whole-body chemical composition of sheep

Hypotheses on total body chemical composition were tested using data from 350 Suffolk sheep grown to a wide range of live weights, and fed in a non-limiting way, or with reduced amounts of feed, or ad libitum on feeds of reduced protein content. The sheep were from an experiment where selection used an index designed to increase the lean deposition rate while restricting the fat deposition rate. Ultrasound muscle and fat depths were the only composition measurements in the index. The animals were males and females from a selection (S) line and its unselected control (C). The protein content of the lipid-free dry matter was unaffected by live weight, sex or feeding treatment with only a very small effect of genetic line (0.762 kg/kg in S and 0.753 kg/kg in C; P < 0.05). The form of the relationship between water and protein was not affected by any of the factors; in the different kinds of sheep it was consistent with no effect other than through differences in mature protein weight. The water : protein ratio at maturity was estimated as 3.45. Over the whole dataset, lipid weight (L) increased with protein weight (P) according to L = 0.3135 × P1.850. Allowing for this scaling, fatness increased on low-protein feeds, was greater in females than in males and in C than in S (P < 0.001). Lipid content (g/kg fleece-free empty body weight) was reduced by restricted feeding only in males at the highest slaughter weight (114 kg). The lines differed in lipid content (P < 0.001) with means of 265.1 g/kg for C and 237.3 g/kg for S. Importantly, there was no interaction between line and feeding treatments. A higher proportion of total body protein was in the carcass in S than in C (0.627 v. 0.610; P < 0.001). For lipid, the difference was reversed (0.736 v. 0.744; P < 0.05). The total energy content increased quadratically with slaughter weight. At a particular weight, the energy content of gain was higher in females than in males and in C than in S. Genetic selection affected body composition at a weight favouring the distribution of protein to the carcass and lipid to the non-carcass. Once allowing for effects of genetic selection, sex and feeding treatment on fatness, simple rules can be used to generate the chemical composition of sheep.     

Correlated Responses to Selection for Postweaning Gain in the Rat

Evidence for correlated responses to selection was investigated in lines of rats selected for 13 generations for high (U line) and low (D line) 3-9-week gain in comparison with random-bred control lines (R and C lines). The increase in 3-9-week gain in the U lines was shown to be due largely to an increase in 9-week weight, although 3-week weight also increased in these lines. In the D lines, where a marked decrease in 3-9-week gain was observed, this was found to be due to a large decrease in 9-week weight and no detectable change in 3-week weight. The average 2-week litter weight, a measure of the lactational performance of the dam, was significanly greater in the U lines than in the D lines. Selection for 3-9-week gain in these lines of rats led to changes of litter size at birth in the same direction as that of selection. This resulted in a significantly higher litter size in the U lines than in the D lines. The number of rats alive 2 and 9 weeks of age and the percentage of mated females pupping were similar in the U and D lines but lower in these lines than the random bred C lines, providing evidence for a reduction of "fitness" in the selected lines. Carcass composition was studied for all lines at the 11th generation of selection. Carcass composition, in terms of water, fat, ash and protein, was similar in the R and C lines. The U lines had more water and lesss fat than the R or C line. The D lines had similar carcass composition to the R and C lines. It is suggested that these selected and random-bred lines of rats are potentially useful animals to investigate further the developmental and physiological mechanisms which control growth.     

The genetics of foraging behaviour: artificial selection for food choice in larvae of the fruitfly,Drosophila melanogaster

Artificial selection for choice between high protein content and high energy content of food was performed for 44 generations of fruitfly larvae. There were significant responses to selection both in a line selected to choose high energy food and in a line selected to choose high protein food. Both lines showed a significantly higher preference for the selected food type than did the control line. The line selected for high energy food also showed a significant increase in response over the generations. Since the selection resulted in lines that differed significantly from controls and from each other, there must be some genetic basis for food choice behaviour. Realized heritability was very low in both selected lines. Viability, as measured by larval weight, pupation time, emergence time and adult size, was significantly higher for flies raised on high protein food than for those raised on high energy food.     

Expression levels of candidate genes for intramuscular fat deposition in two Banna mini-pig inbred lines divergently selected for fatness traits

Intramuscular fat (IMF) content plays an important role in meat quality. Many genes involved in lipid and energy metabolism were identified as candidate genes for IMF deposition, since genetic polymorphisms within these genes were associated with IMF content. However, there is less information on the expression levels of these genes in the muscle tissue. This study aimed at investigating the expression levels of sterol regulating element binding protein-1c (SREBP-1c), diacylglycerol acyltransferase (DGAT-1), heart-fatty acids binding protein (H-FABP), leptin receptor (LEPR) and melanocortin 4 receptor (MC4R) genes and proteins in two divergent Banna mini-pig inbred lines (BMIL). A similar growth performance was found in both the fat and the lean BMIL. The fat meat and IMF content in the fat BMIL were significantly higher than in the lean BMIL, but the lean meat content was lower. The serum triacylglycerol (TAG) and free fatty acid (FFA) contents were significantly higher in the fat than in the lean BMIL. The expression levels of SREBP-1c, DGAT-1 and H-FABP genes and proteins in fat BMIL were increased compared to the lean BMIL. However, the expression levels of LEPR and MC4R genes and proteins were lower.