Altered incubation temperatures between embryonic Days 7 and 13 influence the weights and the mitochondrial respiratory and enzyme activities in breast and leg muscles of broiler embryos

Transcriptome analysis of mRNAs, lncRNAs, and miRNAs in the skeletal muscle of Tibetan chickens at different developmental stages

Introduction: As a valuable genetic resource, native birds can contribute to the sustainable development of animal production. Tibetan chickens, known for their special flavor, are one of the important local poultry breeds in the Qinghai-Tibet Plateau. However, Tibetan chickens have a slow growth rate and poor carcass traits compared with broilers. Although most of the research on Tibetan chickens focused on their hypoxic adaptation, there were fewer studies related to skeletal muscle development. Methods: Here, we performed the transcriptional sequencing of leg muscles from Tibetan chicken embryos at E (embryonic)10, E14, and E18. Results: In total, 1,600, 4,610, and 2,166 DE (differentially expressed) mRNAs, 210, 573, and 234 DE lncRNAs (long non-coding RNAs), and 52, 137, and 33 DE miRNAs (microRNAs) were detected between E10 and E14, E10 and E18, and E14 and E18, respectively. Functional prediction showed several DE mRNAs and the target mRNAs of DE lncRNAs and DE miRNAs were significantly enriched in sarcomere organization, actin cytoskeleton organization, myofibril, muscle fiber development, and other terms and pathways related to muscle growth and development. Finally, a lncRNA-miRNA-mRNA ceRNA (competing endogenous RNA) network associated with muscle growth and development, which contained 6 DE lncRNAs, 13 DE miRNAs, and 50 DE mRNAs, was constructed based on the screened DE RNAs by Gene Ontology (GO) enrichment. These DE RNAs may play a critical regulatory role in the skeletal muscle development of chickens. Discussion: The results provide a genomic resource for mRNAs, lncRNAs, and miRNAs potentially involved in the skeletal muscle development of chickens, which lay the foundation for further studies of the molecular mechanisms underlying skeletal muscle growth and development in Tibetan chickens.

Experimental demonstration of prenatal programming of mitochondrial aerobic metabolism lasting until adulthood

It is increasingly being postulated that among-individual variation in mitochondrial function underlies variation in individual performance (e.g. growth rate) and state of health. It has been suggested (but not adequately tested) that environmental conditions experienced before birth could programme postnatal mitochondrial function, with persistent effects potentially lasting into adulthood. We tested this hypothesis in an avian model by experimentally manipulating prenatal conditions (incubation temperature and stability) and then measuring mitochondrial aerobic metabolism in blood cells from the same individuals during the middle of the growth period and at adulthood. Mitochondrial aerobic metabolism changed markedly across life stages, and parts of these age-related changes were influenced by the prenatal temperature conditions. A high incubation temperature induced a consistent and long-lasting increase in mitochondrial aerobic metabolism. Postnatal mitochondrial aerobic metabolism was positively associated with oxidative damage on DNA but not telomere length. While we detected significant within-individual consistency in mitochondrial aerobic metabolism across life stages, the prenatal temperature regime only accounted for a relatively small proportion (less than 20%) of the consistent among-individual differences we observed. Our results demonstrate that prenatal conditions can programme consistent and long-lasting differences in mitochondrial function, which could potentially underlie among-individual variation in performance and health state.

Prenatal acoustic programming of mitochondrial function for high temperatures in an arid-adapted bird

Sound is an essential source of information in many taxa and can notably be used by embryos to programme their phenotypes for postnatal environments. While underlying mechanisms are mostly unknown, there is growing evidence for the involvement of mitochondria-main source of cellular energy (i.e. ATP)-in developmental programming processes. Here, we tested whether prenatal sound programmes mitochondrial metabolism. In the arid-adapted zebra finch, prenatal exposure to 'heat-calls'-produced by parents incubating at high temperatures-adaptively alters nestling growth in the heat. We measured red blood cell mitochondrial function, in nestlings exposed prenatally to heat- or control-calls, and reared in contrasting thermal environments. Exposure to high temperatures always reduced mitochondrial ATP production efficiency. However, as expected to reduce heat production, prenatal exposure to heat-calls improved mitochondrial efficiency under mild heat conditions. In addition, when exposed to an acute heat-challenge, LEAK respiration was higher in heat-call nestlings, and mitochondrial efficiency low across temperatures. Consistent with its role in reducing oxidative damage, LEAK under extreme heat was also higher in fast growing nestlings. Our study therefore provides the first demonstration of mitochondrial acoustic sensitivity, and brings us closer to understanding the underpinning of acoustic developmental programming and avian strategies for heat adaptation.

Effect of temperature manipulation during incubation on body weight, plasma parameters, muscle histology, and expression of myogenic genes in breast muscle of embryos and broiler chickens from two commercial strains

1. This study evaluated the effect of a higher incubation temperature on body weight, plasma profile, histology and expression of myogenin (MYOG), insulin-like growth factor-I (IGF-I) and vascular endothelial growth factor A (VEGFA) genes in breast muscle of embryos and broilers from two commercial strains.2. A total of 784 eggs from Ross 308 and Cobb 500 broiler breeder flocks were used. Half of the eggs per strain were incubated at control temperature (37.8°C), whereas the other half were exposed to heat treatment (HT) of 38.8°C between embryonic day (ED) 10 and 14, for 6 h/day. Embryos and chicks were sampled on ED 19 and at hatch. A total of 480, one-day-old chicks per strain and incubation temperature were reared up to 42 d post-hatch.3. The HT increased hatch weight of Ross chicks and 42-d body weight of broilers from both strains. Lower plasma triacylglycerol levels were measured for HT embryos and broilers on ED 19 and 42 d post-hatch, respectively. HT reduced plasma T₃ levels in Ross embryos and broilers for the same periods. Hepatic TBARS concentrations were elevated by HT compared to the control incubation.4. The HT reduced breast muscle VEGFA gene expression of Cobb embryos on ED 19, whereas expression was stimulated in day-old chicks. At 42 d post-hatch, fibre area was increased by HT regardless of strain. Compared to the control incubation, HT increased the breast yield of Ross broilers and leg yield of Cobb. Ross-HT broilers had a higher pH at 24 h after slaughter and better water holding capacity than Cobb-HT broilers.5. These results suggested that HT increased body weight, fibre area, IGF-I gene expression and lowered plasma triacylglycerol levels of broiler chickens from both strains at 42 d. However, HT influenced the expression of VEGF-A and MYOG genes and meat quality differently between the broiler strains.

Effects of Dietary Supplementation of gEGF on the Growth Performance and Immunity of Broilers

EGF has been shown to stimulate the growth of animals. In this study, the content of EGF in chicken embryos (gallus EGF, gEGF) aged from 1 to 20 days of incubation were determined by ELISA kit, and the 5-day-old chicken embryos with the highest content of 5593 pg/g were selected to make gEGF crude extracts. A total of 1500 1-day-old Xianju chickens were randomly divided into five groups with six replicates of 50 chickens each. The control group was fed a basal diet, and other treatment diets were supplemented with 4, 8, 16 and 32 ng/kg gEGF crude extract, respectively. The experiment lasted for 30 days. Chicks were harvested at the end of the experiment, and liver, spleen, thymus, bursa and serum samples were collected. Results showed that average daily gain (ADG) and average daily feed intake (ADFI) of 16 ng/kg group were higher than those in the control group (p < 0.05). The serum uric acid (UA) of the 16 ng/kg group was reduced (p < 0.01), and the serum alkaline phosphatase (AKP) of the 16 ng/kg group increased (p < 0.01). The gEGF extract also increased chick's antioxidant capacity, decreased malondialdehyde (MDA) and increased catalase (CAT) in the liver and serum of 16 ng/kg groups in compared to the control group (p < 0.01). Furthermore, immunity was improved by the addition of gEGF to broiler diets. The serum immunoglobin A (IgA) content of 8 and 16 ng/kg groups and the serum immunoglobin M (IgM) content of 4 and 8 ng/kg groups were increased (p < 0.05) compared to the control group. The bursa index of each experimental group was higher than the control group (p < 0.01). These findings demonstrate that the crude extract of gEGF prepared in this experiment could improve the growth performance, antioxidant capacity and immunity of broilers.

miRNAs regulate acute transcriptional changes in broiler embryos in response to modification of incubation temperature

MicroRNAs are post-transcriptional regulators that play critical roles in diverse biological processes. We hypothesize that miRNAs may be involved in regulating transcriptome responses to changes in embryonic incubation temperature in chickens affecting differentiation and proliferation processes during tissue development. Therefore, we conducted comparative transcriptome profiling of miRNAs to examine altered expression in breast and hind muscle of embryos and day 35 chickens experiencing high (38.8 °C), control (37.8 °C), or low (36.8 °C) embryonic incubation temperature during embryonic day (ED) 7–10 or ED10–13. The results revealed differential expression of miRNAs due to modification of embryonic incubation temperature in a muscle type-specific and a developmental stage-specific manner. The immediate effects of thermal change observed in embryos were substantial compared to the subtle long-term effects in chickens at day 35 post-hatch. Upregulation of miR-133 in breast muscle and downregulation of miR-199a-5p, miR-1915, and miR-638 in hind muscle post ED7–10 high-temperature treatment are functionally associated with myogenesis and body size. ED10–13 low-temperature treatment led to downregulation of let-7, miR-93, and miR-130c that are related to proliferation and differentiation. The results provide insight into the dynamics of miRNA expression at variable embryonic incubation temperatures during developmental processes and indicate a major regulatory role of miRNAs in acute responses to modified environmental conditions that affect remodelling of cells and tissues.

Temperature alterations during embryogenesis have a sex-dependent influence on growth properties and muscle metabolism of day-old chicks and 35-day-old broilers

Broiler eggs were either incubated at 37.8°C during the whole incubation period (control), or at higher (38.8°C, group H) and lower temperatures (36.8°C, group L) from embryonic day (ED) 7 up to ED 10 (ED 7 to 10) or from ED 10 up to ED 13 (ED 10 to 13). Before and after this temperature treatment the eggs were incubated at 37.8°C. The day-old chicks were weighted, sexed and fed up to day 35. On days 1 and 35 samples were taken from the breast and leg muscles for analyzing of the mitochondrial respiratory activity (MRA) and from the breast muscles for analysis of the cross-sectional areas (CSA) and the glycogen phosphorylase (GP), phosphofructokinase (PFK), lactate dehydrogenase (LDH), citrate synthase (CS) and cytochrome oxidase (COX) activities. Statistical analysis showed that treatment (control, group H, group L), sex and their interaction, but not the treatment period (ED 7 to 10; ED 10 to 13), significantly influenced the results. Group H chicks had lower (P⩽0.05) body and heart weights but higher (P⩽0.05) liver weights, CSA values, leg MRA as well as PFK, LDH, CS, GP and COX activities compared with the group L chicks. The results of the control chicks differ (P⩽0.05) from those of the group H (body, heart weight, COX), the group L chicks (liver weight, PFK, LDH, CS, GP) or the birds of both other groups (CSA). The group H broiler had higher (P⩽0.05) body and leg weights as well as LDH, CS, COX and GP activities than the group L broilers. The BWs and the LDH and GP results of the control broiler differ (P⩽0.05) from those of both other groups or from the results of the group H (CS) and group L broiler (COX). Female broilers had lower (P⩽0.05) body, breast and leg weights, but higher (P⩽0.05) CSA, LDH, CS and GP activities than the male animals. Analysis of treatment×sex interaction showed that group H hens had higher (P⩽0.05) body and breast weights, LDH and GP activities compared with the group L hens, whereas in the male broiler no effect of the interaction could be found, except for the lower (P⩽0.05) CSA values in the group H than group L cocks. The treatment effects are probably due to altered embryonic activity and related molecular mechanisms. The sex-related differences in the broiler indicate that these alterations already occur in the embryos and chicks, but become significant with the sexual dimorphism after hatch.

Aerobic scope in chicken embryos

We investigated the aerobic scope of chicken embryos, that is, the margin of increase of oxygen consumption ( [Formula: see text] ) above its normal value. [Formula: see text] was measured by an open-flow methodology at embryonic ages E3, E7, E11, E15, E19 and at E20 at the internal (IP) and external pipping (EP) phases, at the normal incubation temperature (Ta=38°C), in hypothermia (Ta=30°C) and in hyperthermia (Ta=41 and 44°C). In the cold, Q₁₀ averaged ~2 at all ages, except in IP and EP when lower values (~1.5) indicated some degree of thermogenesis. In hyperthermia (38-44°C) Q₁₀ was between 1 and 1.4. Hyperthermia had no significant effects on [Formula: see text] whether the results combined all ages or considered individual age groups, except in IP (in which [Formula: see text] increased 8% with 44°C) and EP embryos (+13%). After opening the air cell, which exposed the embryo to a higher O₂ pressure, hyperthermic [Formula: see text] was significantly higher than in normothermia in E19 (+13%), IP (+22%) and EP embryos (+22%). We conclude that in chicken embryos throughout most of incubation neither heat nor oxygen availability limits the normal (normoxic-normothermic) values of [Formula: see text] . Only close to hatching O₂-diffusion represents a limiting factor to the embryo's [Formula: see text] . Hence, embryos differ from postnatal animals for a nearly absent aerobic scope, presumably because their major sources of energy expenditure (growth and tissue maintenance) are constantly maximized.

Transient Shifts of Incubation Temperature Reveal Immediate and Long-Term Transcriptional Response in Chicken Breast Muscle Underpinning Resilience and Phenotypic Plasticity

Variations in egg incubation temperatures can have acute or long-term effects on gene transcription in avian species. Altered gene expression may, in turn, affect muscle traits in poultry and indirectly influence commercial production. To determine how changes in eggshell temperature affect gene expression, incubation temperatures were varied [36.8°C (low), 37.8°C (control), 38.8°C (high)] at specific time periods reflecting two stages of myogenesis [embryonic days (ED) 7-10 and 10-13]. Gene expression was compared between interventions and matching controls by microarrays in broiler breast muscle at ED10 or ED13 and post-hatch at day 35. Early (ED7-10) high incubation temperature (H10ΔC) resulted in 1370 differentially expressed genes (DEGs) in embryos. Ingenuity pathway analysis revealed temporary activation of cell maintenance, organismal development, and survival ability genes, but these effects were not maintained in adults. Late high incubation temperature (ED10-13) (H13ΔC) had slightly negative impacts on development of cellular components in embryos, but a cumulative effect was observed in adults, in which tissue development and nutrition metabolism were affected. Early low incubation temperature (L10ΔC) produced 368 DEGs, most of which were down-regulated and involved in differentiation and formation of muscle cells. In adults, this treatment down-regulated pathways of transcriptional processes, but up-regulated cell proliferation. Late low temperature incubation (L13ΔC) produced 795 DEGs in embryos, and activated organismal survival and post-transcriptional regulation pathways. In adults this treatment activated cellular and organ development, nutrition and small molecule activity, and survival rate, but deactivated size of body and muscle cells. Thermal interventions during incubation initiate immediate and delayed transcriptional responses that are specific for timing and direction of treatment. Interestingly, the transcriptional response to transiently decreased incubation temperature, which did not affect the phenotypes, prompts compensatory effects reflecting resilience. In contrast, higher incubation temperature triggers gene expression and has long-term effects on the phenotype. These mechanisms of considerable phenotypic plasticity contribute to the biodiversity and broaden the basis for managing poultry populations.

Immediate and long-term transcriptional response of hind muscle tissue to transient variation of incubation temperature in broilers

Background

In oviparous species accidental variation of incubation temperatures may occur under natural conditions and mechanisms may have evolved by natural selection that facilitate coping with these stressors. However, under controlled artificial incubation modification of egg incubation temperature has been shown to have a wide-ranging impact on post-hatch development in several poultry species. Because developmental changes initiated in-ovo can affect poultry production, understanding the molecular routes and epigenetic alterations induced by incubation temperature differences may allow targeted modification of phenotypes.

Results

In order to identify molecular pathways responsive to variable incubation temperature, broiler eggs were incubated at a lower or higher temperature (36.8 °C, 38.8 °C) relative to control (37.8 °C) over two developmental intervals, embryonic days (E) 7–10 and 10–13. Global gene expression of M. gastrocnemius was assayed at E10, E13, and slaughter age [post-hatch day (D) 35] (6 groups; 3 time points; 8 animals each) by microarray analysis and treated samples were compared to controls within each time point. Transcript abundance differed for between 113 and 738 genes, depending on treatment group, compared to the respective control. In particular, higher incubation temperature during E7-10 immediately affected pathways involved in energy and lipid metabolism, cell signaling, and muscle development more so than did other conditions. But lower incubation temperature during E10-13 affected pathways related to cellular function and growth, and development of organ, tissue, and muscle as well as nutrient metabolism pathways at D35.

Conclusion

Shifts in incubation temperature provoke specific immediate and long-term transcriptional responses. Further, the transcriptional response to lower incubation temperature, which did not affect the phenotypes, mediates compensatory effects reflecting adaptability. In contrast, higher incubation temperature triggers gene expression and has long-term effects on the phenotype, reflecting considerable phenotypic plasticity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2671-9) contains supplementary material, which is available to authorized users.