Chronic exposure to anabolic steroids induces the muscle expression of oxytocin and a more than fiftyfold increase in circulating oxytocin in cattle

The Pivotal Role of Oxytocin's Mechanism of Thermoregulation in Prader-Willi Syndrome, Schaaf-Yang Syndrome, and Autism Spectrum Disorder

Oxytocin (Oxt) regulates thermogenesis, and altered thermoregulation results in Prader-Willi syndrome (PWS), Schaaf-Yang syndrome (SYS), and Autism spectrum disorder (ASD). PWS is a genetic disorder caused by the deletion of the paternal allele of 15q11-q13, the maternal uniparental disomy of chromosome 15, or defects in the imprinting center of chromosome 15. PWS is characterized by hyperphagia, obesity, low skeletal muscle tone, and autism spectrum disorder (ASD). Oxt also increases muscle tonicity and decreases proteolysis while PWS infants are hypotonic and require assisted feeding in early infancy. This evidence inspired us to merge the results of almost 20 years of studies and formulate a new hypothesis according to which the disruption of Oxt's mechanism of thermoregulation manifests in PWS, SYS, and ASD through thermosensory abnormalities and skeletal muscle tone. This review will integrate the current literature with new updates on PWS, SYS, and ASD and the recent discoveries on Oxt's regulation of thermogenesis to advance the knowledge on these diseases.

Non-canonical Ca2+- Akt signaling pathway mediates the antiproteolytic effects induced by oxytocin receptor stimulation in skeletal muscle

Although it has been previously demonstrated that oxytocin (OXT) receptor stimulation can control skeletal muscle mass in vivo, the intracellular mechanisms that mediate this effect are still poorly understood. Thus, rat oxidative skeletal muscles were isolated and incubated with OXT or WAY-267,464, a non-peptide selective OXT receptor (OXTR) agonist, in the presence or absence of atosiban (ATB), an OXTR antagonist, and overall proteolysis was evaluated. The results indicated that both OXT and WAY-267,464 suppressed muscle proteolysis, and this effect was blocked by the addition of ATB. Furthermore, the WAY-induced anti-catabolic action on protein metabolism did not involve the coupling between OXTR and Gαi since it was insensitive to pertussis toxin (PTX). The decrease in overall proteolysis induced by WAY was probably due to the inhibition of the autophagic/lysosomal system, as estimated by the decrease in LC3 (an autophagic/lysosomal marker), and was accompanied by an increase in the content of Ca2+-dependent protein kinase (PKC)-phosphorylated substrates, pSer473-Akt, and pSer256-FoxO1. Most of these effects were blocked by the inhibition of inositol triphosphate receptors (IP3R), which mediate Ca2+ release from the sarcoplasmic reticulum to the cytoplasm, and triciribine, an Akt inhibitor. Taken together, these findings indicate that the stimulation of OXTR directly induces skeletal muscle protein-sparing effects through a Gαq/IP3R/Ca2+-dependent pathway and crosstalk with Akt/FoxO1 signaling, which consequently decreases the expression of genes related to atrophy, such as LC3, as well as muscle proteolysis.

Oxytocin's Regulation of Thermogenesis May Be the Link to Prader-Willi Syndrome

Prader-Willi Syndrome (PWS) is a genetic neurodevelopmental disorder that is caused by either the deletion of the paternal allele of 15q11-q13, maternal uniparental disomy of chromosome 15 or defects in the chromosome 15 imprinting centre and is characterized by cognitive impairment, hyperphagia and low metabolic rate with significant risk of obesity, as well as a variety of other maladaptive behaviours and autistic spectrum disorder (ASD). Many of the features seen in PWS are thought to be due to hypothalamic dysfunction resulting in hormonal abnormalities and impaired social functioning. The preponderance of evidence indicates that the Oxytocin system is dysregulated in PWS individuals and that this neuropeptide pathways may provide promising targets for therapeutic intervention although the process by which this dysregulation occurs in PWS awaits mechanistic investigation. PWS individuals present abnormalities in thermoregulation an impaired detection for temperature change and altered perception of pain indicating an altered autonomic nervous system. Recent studies indicate that Oxytocin is involved in thermoregulation and pain perception. This review will describe the update on PWS and the recent discoveries on Oxytocin regulation of thermogenesis together with the potential link between Oxytocin regulation of thermogenesis and PWS to create a new groundwork for the treatment of this condition.

Anabolic implants alter abundance of mRNA involved in muscle growth, metabolism, and inflammation in the longissimus of Angus steers in the feedlot

The majority of beef cattle in the United States often receive at least one anabolic implant resulting in improved growth, feed efficiency, and environmental and economic sustainability. However, the physiological and molecular mechanisms through which anabolic implants increase skeletal muscle growth of beef cattle remain elusive. The objective of this study was to identify transcriptional changes occurring in skeletal muscle of steers receiving anabolic implants containing different steroid hormones. Forty-eight steers were stratified by weight into 1 of 4 (n = 12/treatment) implant treatment groups: (1) estradiol (ImpE2; 25.7 mg E2; Compudose, Elanco Animal Health, Greenfield, IN), (2) trenbolone acetate (ImpTBA; 200 mg TBA; Finaplix-H, Merck Animal Health, Madison, NJ), (3) combination (ImpETBA; 120 mg TBA + 24 mg E2; Revalor-S, Merck Animal Health), or (4) no implant (CON). Skeletal muscle biopsies were taken from the longissimus 2 and 10 d post-implantation. The mRNA abundance of 94 genes associated with skeletal muscle growth was examined. At 10 d post-implantation, steers receiving ImpETBA had greater (P = 0.02) myoblast differentiation factor 1 transcript abundance than CON. Citrate synthase abundance was increased (P = 0.04) in ImpETBA steers compared to CON steers. In ImpE2 steers 10 d post-implantation, muscle RING finger protein 1 decreased (P = 0.05) compared to CON steers, and forkhead box protein O4 decreased (P = 0.05) in ImpETBA steers compared to CON steers. Interleukin-6 abundance tended to be increased (P = 0.09) in ImpE2 steers compared to both ImpETBA and CON steers. Furthermore, interleukin-10 mRNA abundance tended to be increased (P = 0.06) in ImpTBA steers compared to ImpETBA steers. Leptin receptor abundance was reduced (P = 0.01) in both ImpE2 and ImpTBA steers when compared to CON steers. Abundance of phosphodiesterase 4B was increased (P = 0.04) in ImpTBA steers compared to CON steers 2 d post-implantation. Taken together, the results of this research demonstrate that estradiol increases skeletal muscle growth via pathways related to nutrient partitioning and mitochondria function, while trenbolone acetate improves steer skeletal muscle growth via pathways related to muscle growth.

Transcriptome-based analysis of early post-mortem formation of pale, soft, and exudative (PSE) pork

Pale, soft, and exudative (PSE) meat can cause consumer dissatisfaction and economic losses. This study determined meat quality, glycolytic enzyme activity, and differential gene expression in the longissimus lumborum (LL) and semimembranosus (SM) of normal and PSE pork carcasses. The SM did not result in PSE meat. Hexokinase, lactate dehydrogenase, and pyruvate kinase activities were lower in the SM of PSE carcasses than in the normal carcasses. Functional enrichment analysis revealed that immune, inflammatory, and muscle fibre genes were significantly enriched in PSE pork. More specifically, PPP1R3G and MSS51 may be key genes regulating pork quality in the SM. Meanwhile, the differential expression of PLVAB, ADIPOQ, LEP, MYH4, MYH7, MYL3, MYL6B, FOS, ATF3, and HSPA6 may induce PSE formation in the LL. These results may provide insights into PSE pork formation mechanisms and reveal candidate genes for improving meat quality after validation.

The successful use of -omic technologies to achieve the 'One Health' concept in meat producing animals

Human health and wellbeing are closely linked to healthy domestic animals, a vital wildlife, and an intact ecosystem. This holistic concept is referred to as 'One Health'. In this review, we provide an overview of the potential and the challenges for the use of modern -omics technologies, especially transcriptomics and proteomics, to implement the 'One Health' idea for food-producing animals. These high-throughput studies offer opportunities to find new potential molecular biomarkers to monitor animal health, detect pharmacological interventions and evaluate the wellbeing of farm animals in modern intensive livestock systems.

Cattle breed type and anabolic implants impact calpastatin expression and abundance of mRNA associated with protein turnover in the longissimus thoracis of feedlot steers

Two methods that the beef cattle industry can use to improve efficiency, sustainability, and economic viability are growth promotants and crossbreeding cattle of different breed types. In the United States, over 90% of cattle receive an anabolic implant at some point during production resulting in an overall increase in skeletal muscle growth. Recent research suggests that the two main cattle breed types, Bos indicus and Bos taurus, respond differently to anabolic implants. The objective of this study was to characterize changes that occur in skeletal muscle following implanting in Bos indicus influenced steers or Bos taurus steers. Twenty steers were stratified by initial weight in a 2 × 2 factorial design examining two different breeds: Angus (AN; n = 10) or Santa Gertrudis influenced (SG; n = 10), and two implant strategies: no implant (CON; n = 10) or a combined implant containing 120 mg TBA and 24 mg E2 (IMP; n = 10; Revalor-S, Merck Animal Health). Skeletal muscle biopsies were taken from the longissimus thoracis (LT) 2 and 10 d post-implantation. The mRNA abundance of 24 genes associated with skeletal muscle growth were examined, as well as the protein expression of µ-calpain and calpastatin. Succinate dehydrogenase mRNA abundance was impacted (P = 0.05) by a breed × treatment interaction 2 d post-implanting, with SG-CON having a greater increased abundance than all other steers. A tendency for a breed × treatment interaction was observed for calpain-6 mRNA (P = 0.07), with SG-CON having greater abundance than AN-CON and SG-IMP. Additionally, calpastatin protein expression was altered (P = 0.01) by a breed × treatment interaction, with SG-CON and SG-IMP steers having increased expression (P = 0.01) compared with AN-CON steers. At 2 d post-implanting, a breed × treatment interaction was observed with SG-CON steers having greater (P = 0.05) mRNA abundance of mitogen-activated protein kinase compared with AN-CON steers. Furthermore, breed affected (P = 0.05) calpastatin abundance with AN steers having increased (P = 0.05) abundance 2 d post-implanting compared with SG steers. Meanwhile, implants tended to affect (P = 0.09) muscle RING finger protein-1 mRNA abundance, with CON steers having increased (P = 0.09) abundance compared with that of IMP steers. These findings suggest that cattle breed type and anabolic implants impact calpastatin expression and mRNA abundance associated with protein turnover in the LT of feedlot steers 2 and 10 d post-implantation.

The Importance of Experimental Investigation of the Peripheral Oxytocin System

Oxytocin and oxytocin receptors are synthesized in the periphery where paracrine/autocrine actions have been described alongside endocrine actions effected by central release of oxytocin from the posterior pituitary. In the female reproductive system, classical actions of uterine contraction and milk ejection from mammary glands are accompanied by actions in the ovaries where roles in steroidogenesis, follicle recruitment and ovulation have been described. Steroidogenesis, contractile activity, and gamete health are similarly affected by oxytocin in the male reproductive tract. In the cardiovascular system, a local oxytocinergic system appears to play an important cardio-protective role. This role is likely associated with emerging evidence that peripheral oxytocin is an important hormone in the endocrinology of glucose homeostasis due to its actions in adipose, the pancreas, and the largely ignored oxytocinergic systems of the adrenal glands and liver. Gene polymorphisms are shown to be associated with a number of reported traits, not least factors associated with metabolic syndrome.

Oxytocin induces anti-catabolic and anabolic effects on protein metabolism in the female rat oxidative skeletal muscle

AIMS

Although it is well established that skeletal muscle contains oxytocin (OT) receptors and OT-knockout mice show premature development of sarcopenia, the role of OT in controlling skeletal muscle mass is still unknown. Therefore, the present work aimed to determine OT's effects on skeletal muscle protein metabolism.

MAIN METHODS

Total proteolysis, proteolytic system activities and protein synthesis were assessed in isolated soleus muscle from prepubertal female rats. Through in vivo experiments, rats received 3-day OT treatment (3UI.kg^-1.day^-1, i.p.) or saline, and muscles were harvested for mass-gain assessment.

KEY FINDINGS

In vitro OT receptor stimulation reduced total proteolysis, specifically through attenuation of the lysosomal and proteasomal proteolytic systems, and in parallel activated the Akt/FoxO1 signaling and suppressed atrogenes (e.g., MuRF-1 and atrogin-1) expression induced by motor denervation. On the other hand, the protein synthesis was not altered by in vitro treatment with the OT receptor-selective agonist. Although short-term OT treatment did not change the atrogene mRNA levels, the protein synthesis was stimulated, resulting in soleus mass gain, probably through an indirect effect.

SIGNIFICANCE

Taken together, these data show for the first time that OT directly inhibits the proteolytic activities of the lysosomal and proteasomal systems in rat oxidative skeletal muscle by suppressing atrogene expression via stimulation of Akt/FoxO signaling. Moreover, the data obtained from in vivo experiments suggest OT's ability to control rat oxidative skeletal muscle mass.

The New Frontier in Oxytocin Physiology: The Oxytonic Contraction

Oxytocin (Oxt) is a nine amino acid peptide important in energy regulation and is essential to stress-related disorders. Specifically, low Oxt levels are associated with obesity in human subjects and diet-induced or genetically modified animal models. The striking evidence that Oxt is linked to energy regulation is that Oxt- and oxytocin receptor (Oxtr)-deficient mice show a phenotype characterized by late onset obesity. Oxt-/- or Oxtr-/- develop weight gain without increasing food intake, suggesting that a lack of Oxt reduce metabolic rate. Oxt is differentially expressed in skeletal muscle exerting a protective effect toward the slow-twitch muscle after cold stress challenge in mice. We hypothesized that Oxt potentiates the slow-twitch muscle as it does with the uterus, triggering "the oxytonic contractions". Physiologically, this is important to augment muscle strength in fight/flight response and is consistent with the augmented energetic need at time of labor and for the protection of the offspring when Oxt secretion spikes. The normophagic obesity of Oxt-/- or Oxtr-/- mice could have been caused by decreased skeletal muscle tonicity which drove the metabolic phenotype. In this review, we summarized our findings together with the recent literature on this fascinating subjects in a "new oxytonic perspective" over the physicology of Oxt.

Neurohypophyseal hormones and skeletal muscle: a tale of two faces

The neurohypophyseal hormones vasopressin and oxytocin were invested, in recent years, with novel functions upon striated muscle, regulating its differentiation, trophism, and homeostasis. Recent studies highlight that these hormones not only target skeletal muscle but represent novel myokines. We discuss the possibility of exploiting the muscle hypertrophying activity of oxytocin to revert muscle atrophy, including cancer cachexia muscle wasting. Furthermore, the role of oxytocin in cardiac homeostasis and the possible role of cardiac atrophy as a concause of death in cachectic patients is discussed.

Oxytocin/Osteocalcin/IL-6 and NGF/BDNF mRNA Levels in Response to Cold Stress Challenge in Mice: Possible Oxytonic Brain-Bone-Muscle-Interaction

Oxytocin (Oxt), osteocalcin (Ost), and NGF/BDNF have a role in bone homeostasis, reproduction, and cognition. Oxt/Ost is required for muscle repair. We investigated gene response of muscle and the inter-organ communication following cold stress (CS). The mRNA quantity of Ngf, Ost, Oxt, Bdnf, p75ntr, Ntrk1, Gprc6a, Oxtr, Ntrk2, UCP1, and Il-6 genes in bone, brain, soleus (SOL), and tibialis anterior (TA) muscles from adult mice following CS were investigated. The myosin heavy-chain Mhc2b, Mhc1, Mhc2x, and Mhc2a gene expression were investigated. Mice were maintained at T = 23°C or 4°C for 6 h and 5-days (5d). CS mice did not show signs of muscle degeneration. An upregulation of Ucp1 and Ngf genes by 2 and 1.5 folds, respectively, in TA after 6 h CS and Ntrk1 by 4 and 22 folds in SOL muscle after 6 h and 5d CS, respectively, was observed; while after 6 h CS p75Ntr was downregulated in either muscle. Bdnf was unaffected, while after 5d CS Ntrk2 was upregulated in TA. Ost was downregulated in SOL by 0.9-folds at 5d. Following 5d CS, Oxtr and Il-6 genes were upregulated, respectively, by 1 and 1.5 folds in SOL. A downregulation of Mhc2b, respectively, by 0.96 and 0.88-folds after 6 h and 5d CS in SOL and Mhc2a was also downregulated by 0.88-fold after 5d CS in TA. Mhc1 and Mhc2x were not affected. Changes in the expression levels of genes in TA and SOL muscles, bone, and brain following CS were regulated by IL6 and Oxt. CS potentiates the slow-twitch phenotype of SOL which is in line with the metabolic need of this muscle, and the potentiation of the slow-twitch phenotype in TA. Oxt and IL6 coordinate a phenotype-dependent tonic effect of slow-twitch muscle and Oxt regulates the inter-organ interaction between brain and SOL muscle. Muscle tropism is maintained by NGF signaling following CS.

Gene expression profiling and identification of hub genes in Nellore cattle with different marbling score levels

The marbling rate evaluation is difficult and expensive, requiring slaughter of the animal or ultrasound measurement. Thus, this trait is generally not included in animal breeding programs. The use of molecular techniques to elucidate intramuscular fat deposition may help improve this trait. In this respect, transcriptome studies and differential gene expression analysis by RNA-Seq can contribute to advances in this area. The objective of this study was to use RNA-Seq to identify differentially expressed genes (DEGs) in muscle tissue (longissimus thoracis) of Nellore cattle divergently ranked on marbling, in order to increase our understanding of genes involved in the expression of this trait. The results revealed 49 DEGs and three hub genes (CISH, UFM1, TSHZ1), all of them involved in insulin and diabetes mellitus metabolism. These results indicating key genes and pathways, which may help to develop strategies designed to select animals with greater marbling.

Systems Biology Reveals NR2F6 and TGFB1 as Key Regulators of Feed Efficiency in Beef Cattle

Systems biology approaches are used as strategy to uncover tissue-specific perturbations and regulatory genes related to complex phenotypes. We applied this approach to study feed efficiency (FE) in beef cattle, an important trait both economically and environmentally. Poly-A selected RNA of five tissues (adrenal gland, hypothalamus, liver, skeletal muscle and pituitary) of eighteen young bulls, selected for high and low FE, were sequenced (Illumina HiSeq 2500, 100 bp, pared-end). From the 17,354 expressed genes considering all tissues, 1,335 were prioritized by five selection categories (differentially expressed, harboring SNPs associated with FE, tissue-specific, secreted in plasma and key regulators) and used for network construction. NR2F6 and TGFB1 were identified and validated by motif discovery as key regulators of hepatic inflammatory response and muscle tissue development, respectively, two biological processes demonstrated to be associated with FE. Moreover, we indicated potential biomarkers of FE, which are related to hormonal control of metabolism and sexual maturity. By using robust methodologies and validation strategies, we confirmed the main biological processes related to FE in Bos indicus and indicated candidate genes as regulators or biomarkers of superior animals.

Oxytocin in metabolic homeostasis: implications for obesity and diabetes management

Oxytocin was once understood solely as a neuropeptide with a central role in social bonding, reproduction, parturition, lactation and appetite regulation. Recent evidence indicates that oxytocin enhances glucose uptake and lipid utilization in adipose tissue and skeletal muscle, suggesting that dysfunction of the oxytocin system could underlie the pathogenesis of insulin resistance and dyslipidaemia. Murine studies revealed that deficiencies in oxytocin signalling and oxytocin receptor expression lead to obesity despite normal food intake, motor activity and increased leptin levels. In addition, plasma oxytocin concentration is notably lower in obese individuals with diabetes, which may suggest an involvement of the oxytocin system in the pathogenesis of cardiometabolic disease. More recently, small scale studies demonstrated that intranasal administration of oxytocin was associated with significant weight loss as well as improvements in insulin sensitivity and pancreatic β-cell responsivity in human subjects. The multi-pronged effects of oxytocin signalling on improving peripheral insulin sensitivity, pancreatic function and lipid homeostasis strongly suggest a role for this system as a therapeutic target in obesity and diabetes management. The complexity of obesity aetiology and the pathogenesis of obesity-related metabolic complications underscore the need for a systems approach to better understand the role of oxytocin in metabolic function.

Oxytocin is involved in steroid hormone-stimulated bovine satellite cell proliferation and differentiation in vitro

Sex steroid hormones are used in the meat industry due to their ability to regulate muscle hypertrophy. However, the mechanisms underlying their action are not fully elucidated. Recent reports demonstrate that steroid hormones increase oxytocin (OXT) expression in skeletal muscle, indicating that OXT may play a role in satellite cell activity. This hypothesis was tested using steroid hormones (17β-estradiol [E2]; trenbolone acetate [TBA]), tamoxifen (TAM), OXT, and atosiban (A: OXT receptor inhibitor) applied to bovine satellite cells (BSCs) to investigate BSC regulation by OXT. Oxytocin alone increased fusion index (P < 0.05) but not BSC proliferation. Oxytocin reduced (P < 0.05) apoptotic nuclei and stimulated migration rate (P < 0.05). Similarly, E2 and TBA increased (P < 0.05) BSC proliferation rate, fusion index, and migration and decreased (P < 0.05) apoptotic nuclei. 17β-Estradiol or TBA supplemented with A had lower (P < 0.05) BSC proliferation rate, fusion index, and migration and more (P < 0.05) apoptotic nuclei compared with E2 or TBA alone. Furthermore, OXT expression increased (P < 0.05) in E2 or TBA-treated proliferating BSC. Oxytocin, E2, and TBA increased (P < 0.05) MyoD and MyoG expression in proliferating BSC. During BSC differentiation, OXT expression increased (P < 0.05) with E2 or TBA treatments. MyoG expression increased (P < 0.05) in OXT, E2, and TBA compared with control. However, A, OXT + A, TAM, TAM + OXT, E2 + TAM, E2 + A, and TBA + A decreased (P < 0.05) MyoG expression during BSC differentiation. These results indicate that OXT is involved in steroid hormone-stimulated BSC activity.

New surveillance concepts in food safety in meat producing animals: the advantage of high throughput 'omics' technologies - A review

The misuse of anabolic hormones or illegal drugs is a ubiquitous problem in animal husbandry and in food safety. The ban on growth promotants in food producing animals in the European Union is well controlled. However, application regimens that are difficult to detect persist, including newly designed anabolic drugs and complex hormone cocktails. Therefore identification of molecular endogenous biomarkers which are based on the physiological response after the illicit treatment has become a focus of detection methods. The analysis of the ‘transcriptome’ has been shown to have promise to discover the misuse of anabolic drugs, by indirect detection of their pharmacological action in organs or selected tissues. Various studies have measured gene expression changes after illegal drug or hormone application. So-called transcriptomic biomarkers were quantified at the mRNA and/or microRNA level by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) technology or by more modern ‘omics’ and high throughput technologies including RNA-sequencing (RNA-Seq). With the addition of advanced bioinformatical approaches such as hierarchical clustering analysis or dynamic principal components analysis, a valid ‘biomarker signature’ can be established to discriminate between treated and untreated individuals. It has been shown in numerous animal and cell culture studies, that identification of treated animals is possible via our transcriptional biomarker approach. The high throughput sequencing approach is also capable of discovering new biomarker candidates and, in combination with quantitative RT-qPCR, validation and confirmation of biomarkers has been possible. These results from animal production and food safety studies demonstrate that analysis of the transcriptome has high potential as a new screening method using transcriptional ‘biomarker signatures’ based on the physiological response triggered by illegal substances.

Molecular regulation of high muscle mass in developing Blonde d'Aquitaine cattle foetuses

The Blonde d'Aquitaine (BA) is a French cattle breed with enhanced muscularity, partly attributable to a MSTN mutation. The BA m. Semitendinosus has a faster muscle fibre isoform phenotype comprising a higher proportion of fast type IIX fibres compared to age-matched Charolais (CH). To better understand the molecular network of modifications in BA compared to CH muscle, we assayed the transcriptomes of the m. Semitendinosus at 110, 180, 210 and 260 days postconception (dpc). We used a combination of differential expression (DE) and regulatory impact factors (RIF) to compare and contrast muscle gene expression between the breeds. Prominently developmentally regulated genes in both breeds reflected the replacement of embryonic myosin isoforms (MYL4, MYH3) with adult isoforms (MYH1) and the upregulation of mitochondrial metabolism (CKMT2, AGXT2L1) in preparation for birth. However, the transition to a fast, glycolytic muscle phenotype in the MSTN mutant BA is detectable through downregulation of various slow twitch subunits (TNNC1, MYH7, TPM3, CSRP3) beyond 210 dpc, and a small but consistent genome-wide reduction in mRNA encoding the mitoproteome. Across the breeds, NRIP2 is the regulatory gene possessing a network change most similar to that of MSTN.

Summary: We explored the molecular basis of high muscle mass in Blonde d’Aquitaine cattle, and found that mRNA encoding slow fibres and mitochondrial proteins were downregulated in this breed.

TRIENNIAL GROWTH AND DEVELOPMENT SYMPOSIUM: Intramuscular fat deposition in ruminants and pigs: A transcriptomics perspective

The genomics era has led to an explosion in the study of gene expression in production animals. Intramuscular fat (IMF) content (both high and low) and composition are major quality attributes of meat, and more than 90 transcriptomic studies of IMF deposition have been undertaken in the ruminants and pigs since 2001, with the majority since 2008. The studies have implicated many genes involved in the control of adipogenesis, lipogenesis, and deposition of IMF, but there is relatively little consistency between the different studies. However, the genes encoding the synthesis enzymes acetyl-CoA carboxylase α, fatty acid synthase, and stearoyl-CoA desaturase; the fatty acid binding protein 4; the potential signaling protein thyroid hormone responsive; and the regulators C/EBPα, PPARγ, and sterol regulatory element binding transcription factor 1 are supported by 5 or more of the 90 studies. By combining the results of all the studies, complete pathways for long-chain fatty acid (LCFA) and triacylglyceride (TAG) synthesis are identified, as are a number of genes encoding proteins probably associated with the storage of TAG and genes encoding a number of known and potential adipokines. In contrast, support for the association of lipolytic pathways with IMF percentage is less strong. Differences in experimental design-in particular, the age of the animals, the rate of IMF deposition at sampling, the past nutritional history of the animals used, and the complexities of using a tissue with mixed cell types-have contributed to the differences in results and interpretation. Biomarkers predictive of future IMF percentage, facilitating reaching optimal IMF content at slaughter, may have industry utility, but to be useful in animal biopsy and postslaughter samples, where multiple cell types are present, genes must be carefully chosen to ensure that they are informative about the expected processes. Despite these problems, candidate biomarkers for estimation of de novo intramuscular adipocyte LCFA synthesis, LCFA uptake rate by intramuscular adipocytes, and IMF deposition rate have been identified and examples of their utility have been published. However, further work is required to demonstrate how best to apply the assays for the benefit of the relevant livestock production industries.

17β-estradiol upregulates oxytocin and the oxytocin receptor in C2C12 myotubes

Background

The endocrinology of skeletal muscle is highly complex and many issues about hormone action in skeletal muscle are still unresolved. Aim of the work is to improve our knowledge on the relationship between skeletal muscle and 17β-estradiol.

Methods

The skeletal muscle cell line C2C12 was treated with 17β-estradiol, the oxytocin peptide and a combination of the two hormones. The mRNA levels of myogenic regulatory factors, myosin heavy chain, oxytocin, oxytocin receptor and adipogenic factors were analysed in C2C12 myotubes.

Results

It was demonstrated that C2C12 myoblasts and myotubes express oxytocin and its receptor, in particular the receptor levels physiologically increase in differentiated myotubes. Myotubes treated with 17β-estradiol overexpressed oxytocin and oxytocin receptor genes by approximately 3- and 29-fold, respectively. A decrease in the expression of fatty acid binding protein 4 (0.62-fold), a fat metabolism-associated gene, was observed in oxytocin-treated myotubes. On the contrary, fatty acid binding protein 4 was upregulated (2.66-fold) after the administration of the combination of 17β-estradiol and oxytocin. 17β-estradiol regulates oxytocin and its receptor in skeletal muscle cells and they act in a synergic way on fatty acid metabolism.

Discussion

Oxytocin and its receptor are physiologically regulated along differentiation. 17β-estradiol regulates oxytocin and its receptor in skeletal muscle cells. 17β-estradiol and oxytocin act in a synergic way on fatty acid metabolism. A better understanding of the regulation of skeletal muscle homeostasis by estrogens and oxytocin peptide could contribute to increase our knowledge of muscle and its metabolism.

Morphological Examination and Transcriptomic Profiling To Identify Prednisolone Treatment in Beef Cattle

In livestock production corticosteroids are licensed only for therapy; nevertheless, they are often illegally used as growth promoters. The aim of this study was to identify morphological or biomolecular alterations induced by prednisolone (PDN) in experimentally treated beef cattle, because PDN and its metabolites are no longer detectable by LC-MS/MS methods in biological fluids. Moreover, PDN does not induce any histological alterations in the thymus, different from dexamethasone treatments. Therefore, a marker of illicit treatment for this growth promoter could be useful. Eight male Italian Friesian beef cattle were administered prednisolone acetate 30 mg day^-1 per os for 35 days, and seven beef cattle represented the control group. Six days after drug withdrawal, the animals were slaughtered. Morphological and morphometric modifications were evaluated in the epididymis and testis, whereas transcriptomic changes induced by PDN administration were investigated in peripheral blood mononuclear cells (PBMCs) at different sampling times and in skeletal muscle and testis sampled at slaughtering. In the epididymis, spermatozoa number decreased in PDN-treated animals, and in some cases they were totally absent. Correspondingly, in the testis of treated animals, down-regulation for serine/threonine kinase 11 (STK11) gene expression was detected (p < 0.01). DNA microarray analysis revealed a total of 133 differentially expressed genes in skeletal muscle and testis, and 907 and 1416 in PBMCs after 33 days of treatment and at slaughtering, respectively. Histological investigations on epididymal content could represent a promising marker for PDN treatment in beef cattle and could be used as a screening method to identify animals worthy of further investigation with official methods. Moreover, the clear transcriptomic signature of PDN treatment evidenced in PBMCs supported the possibility of using this matrix to monitor the illicit treatment in vivo during ranching.

The transcriptome of muscle and liver is responding differently to a combined trenbolone acetate and estradiol implant in cattle

We investigated the transcriptomic signature of some anabolic steroids in cattle. Our main objective was to evaluate the effect of a combined trenbolone acetate (TBA, 200mg) and estradiol-17β (E2, 40 mg) implant (Revalor-XS®, REV) on the transcriptome of muscle (target tissue for anabolic steroids) and liver (main biotransformation site). Transcriptomic profiling was performed on 60 samples (30 per tissue) representing 2 groups of animals: REV (sustained release implant for 71 days, n=15), and a control group (CTR, n=15). The analyses (REV vs. CTR) evidenced the differential expression of 431 (down-regulated) and 503 transcripts (268 up-regulated and 235 down-regulated) in muscle and liver tissues, respectively. Functional annotation showed the enrichment of several ion transport systems (cation, metal ion and potassium ion transport) in muscle, while revealing the enrichment of carbohydrate, protein and glycoprotein metabolism and biosynthesis mechanisms in the liver. Both tissues had 20 genes commonly expressed in-between. Seven randomly-selected genes showed positive correlation with their corresponding microarray data upon a qPCR cross-validation step. In muscle, but not the liver, Principal Component Analysis (PCA) on the microarray data resulted in the separation of treated animals from the untreated ones (first 2 components=97.87%.). Overall, the identification of different genes, pathways and biological processes has illustrated the distinctive transcriptomic profile of muscle and liver in response to anabolic steroids. Moreover, it is becoming more clear that anabolic steroids are working through a complex interaction of numerous pathways and processes incorporating different tissues.

Associations of SNPs located at candidate genes to bovine growth traits, prioritized with an interaction networks construction approach

Background

For most domestic animal species, including bovines, it is difficult to identify causative genetic variants involved in economically relevant traits. The candidate gene approach is efficient because it investigates genes that are expected to be associated with the expression of a trait and defines whether the genetic variation present in a population is associated with phenotypic diversity. A potential limitation of this approach is the identification of candidates. This study used a bioinformatics approach to identify candidate genes via a search guided by a functional interaction network.

Results

A functional interaction network tool, BosNet, was constructed for Bos taurus. Predictions for candidate genes were performed using the guilt-by-association principle in BosNet. Association analyses identified five novel markers within BosNet-prioritized genes that had significant effects on different growth traits in Charolais and Brahman cattle.

Conclusions

BosNet is an excellent tool for the identification of single nucleotide polymorphisms that are potentially associated with complex traits.

Transcriptome analysis of cattle muscle identifies potential markers for skeletal muscle growth rate and major cell types

BACKGROUND

This study aimed to identify markers for muscle growth rate and the different cellular contributors to cattle muscle and to link the muscle growth rate markers to specific cell types.

RESULTS

The expression of two groups of genes in the longissimus muscle (LM) of 48 Brahman steers of similar age, significantly enriched for "cell cycle" and "ECM (extracellular matrix) organization" Gene Ontology (GO) terms was correlated with average daily gain/kg liveweight (ADG/kg) of the animals. However, expression of the same genes was only partly related to growth rate across a time course of postnatal LM development in two cattle genotypes, Piedmontese x Hereford (high muscling) and Wagyu x Hereford (high marbling). The deposition of intramuscular fat (IMF) altered the relationship between the expression of these genes and growth rate. K-means clustering across the development time course with a large set of genes (5,596) with similar expression profiles to the ECM genes was undertaken. The locations in the clusters of published markers of different cell types in muscle were identified and used to link clusters of genes to the cell type most likely to be expressing them. Overall correspondence between published cell type expression of markers and predicted major cell types of expression in cattle LM was high. However, some exceptions were identified: expression of SOX8 previously attributed to muscle satellite cells was correlated with angiogenesis. Analysis of the clusters and cell types suggested that the "cell cycle" and "ECM" signals were from the fibro/adipogenic lineage. Significant contributions to these signals from the muscle satellite cells, angiogenic cells and adipocytes themselves were not as strongly supported. Based on the clusters and cell type markers, sets of five genes predicted to be representative of fibro/adipogenic precursors (FAPs) and endothelial cells, and/or ECM remodelling and angiogenesis were identified.

CONCLUSIONS

Gene sets and gene markers for the analysis of many of the major processes/cell populations contributing to muscle composition and growth have been proposed, enabling a consistent interpretation of gene expression datasets from cattle LM. The same gene sets are likely to be applicable in other cattle muscles and in other species.

Contextual modulation of social and endocrine correlates of fitness: insights from the life history of a sex changing fish

Steroid hormones are critical regulators of reproductive life history, and the steroid sensitive traits (morphology, behavior, physiology) associated with particular life history stages can have substantial fitness consequences for an organism. Hormones, behavior and fitness are reciprocally associated and can be used in an integrative fashion to understand how the environment impacts organismal function. To address the fitness component, we highlight the importance of using reliable proxies of reproductive success when studying proximate regulation of reproductive phenotypes. To understand the mechanisms by which the endocrine system regulates phenotype, we discuss the use of particular endocrine proxies and the need for appropriate functional interpretation of each. Lastly, in any experimental paradigm, the responses of animals vary based on the subtle differences in environmental and social context and this must also be considered. We explore these different levels of analyses by focusing on the fascinating life history transitions exhibited by the bi-directionally hermaphroditic fish, Lythrypnus dalli. Sex changing fish are excellent models for providing a deeper understanding of the fitness consequences associated with behavioral and endocrine variation. We close by proposing that local regulation of steroids is one potential mechanism that allows for the expression of novel phenotypes that can be characteristic of specific life history stages. A comparative species approach will facilitate progress in understanding the diversity of mechanisms underlying the contextual regulation of phenotypes and their associated fitness correlates.

Neurohypophyseal Hormones: Novel Actors of Striated Muscle Development and Homeostasis

Since the 1980’s, novel functional roles of the neurohypophyseal hormones vasopressin and oxytocin have emerged. Several studies have investigated the effects of these two neurohormones on striated muscle tissues, both in vitro and in vivo. The effects of vasopressin on skeletal myogenic cells, developing muscle and muscle homeostasis have been documented. Oxytocin appears to have a greater influence on cardiomyocite differentiation and heart homeostasis. This review summarizes the studies on these novel roles of the two neurohypophyseal hormones, and open the possibility of new therapeutic approaches for diseases affecting striated muscle.

Local overexpression of V1a-vasopressin receptor enhances regeneration in tumor necrosis factor-induced muscle atrophy

Skeletal muscle atrophy occurs during disuse and aging, or as a consequence of chronic diseases such as cancer and diabetes. It is characterized by progressive loss of muscle tissue due to hypotrophic changes, degeneration, and an inability of the regeneration machinery to replace damaged myofibers. Tumor necrosis factor (TNF) is a proinflammatory cytokine known to mediate muscle atrophy in many chronic diseases and to inhibit skeletal muscle regeneration. In this study, we investigated the role of Arg-vasopressin-(AVP-)dependent pathways in muscles in which atrophy was induced by local overexpression of TNF. AVP is a potent myogenesis-promoting factor and is able to enhance skeletal muscle regeneration by stimulating Ca(2+)/calmodulin-dependent kinase and calcineurin signaling. We performed morphological and molecular analyses and demonstrated that local over-expression of the AVP receptor V1a enhances regeneration of atrophic muscle. By upregulating the regeneration/differentiation markers, modulating the inflammatory response, and attenuating fibrogenesis, the stimulation of AVP-dependent pathways creates a favourable environment for efficient and sustained muscle regeneration and repair even in the presence of elevated levels of TNF. This study highlights a novel in vivo role for AVP-dependent pathways, which may represent an interesting strategy to counteract muscle decline in aging or in muscular pathologies.

Transcriptomic profiling as a screening tool to detect trenbolone treatment in beef cattle

The effects of steroid hormone implants containing trenbolone alone (Finaplix-H), combined with 17β-oestradiol (17β-E; Revalor-H), or with 17β-E and dexamethasone (Revalor-H plus dexamethasone per os) on the bovine muscle transcriptome were examined by DNA-microarray. Overall, large sets of genes were shown to be modulated by the different growth promoters (GPs) and the regulated pathways and biological processes were mostly shared among the treatment groups. Using the Prediction Analysis of Microarray program, GP-treated animals were accurately identified by a small number of predictive genes. A meta-analysis approach was also carried out for the Revalor group to potentially increase the robustness of class prediction analysis. After data pre-processing, a high level of accuracy (90%) was obtained in the classification of samples, using 105 predictive gene markers. Transcriptomics could thus help in the identification of indirect biomarkers for anabolic treatment in beef cattle to be applied for the screening of muscle samples collected after slaughtering.

RNF14 is a regulator of mitochondrial and immune function in muscle

BACKGROUND

Muscle development and remodelling, mitochondrial physiology and inflammation are thought to be inter-related and to have implications for metabolism in both health and disease. However, our understanding of their molecular control is incomplete.

RESULTS

In this study we have confirmed that the ring finger 14 protein (RNF14), a poorly understood transcriptional regulator, influences the expression of both mitochondrial and immune-related genes. The prediction was based on a combination of network connectivity and differential connectivity in cattle (a non-model organism) and mice data sets, with a focus on skeletal muscle. They assigned similar probability to mammalian RNF14 playing a regulatory role in mitochondrial and immune gene expression. To try and resolve this apparent ambiguity we performed a genome-wide microarray expression analysis on mouse C2C12 myoblasts transiently transfected with two Rnf14 transcript variants that encode 2 naturally occurring but different RNF14 protein isoforms. The effect of both constructs was significantly different to the control samples (untransfected cells and cells transfected with an empty vector). Cluster analyses revealed that transfection with the two Rnf14 constructs yielded discrete expression signatures from each other, but in both cases a substantial set of genes annotated as encoding proteins related to immune function were perturbed. These included cytokines and interferon regulatory factors. Additionally, transfection of the longer transcript variant 1 coordinately increased the expression of 12 (of the total 13) mitochondrial proteins encoded by the mitochondrial genome, 3 of which were significant in isolated pair-wise comparisons (Mt-coxII, Mt-nd2 and mt-nd4l). This apparent additional mitochondrial function may be attributable to the RWD protein domain that is present only in the longer RNF14 isoform.

CONCLUSIONS

RNF14 influences the expression of both mitochondrial and immune related genes in a skeletal muscle context, and has likely implications for the inter-relationship between bioenergetic status and inflammation.

Oxytocin precursor gene expression in bovine skeletal muscle is regulated by 17β-oestradiol and dexamethasone

Growth promoter administration, in livestock, potentially poses a major threat to public health, due to the potential endocrine and carcinogenic activity of residues, accumulating in edible tissues, such as skeletal muscle. Therefore, development of new screening tests and methods for the detection of illicit treatments of food animals would be useful. In this study the serum concentrations of oxytocin peptide were measured in beef cattle receiving 17β oestradiol, dexamethasone or placebo over a period of 40 days. Changes in gene expression of oxytocin precursor in skeletal muscle were also examined in these animals. Serum analysis using an oxytocin EIA kit indicated a significant up-regulation of the biosynthesis of this nonapeptide only in cattle after 17β oestradiol, but not after dexamethasone or placebo treatment. Quantitative PCR (qPCR) analysis showed a significant overexpression of the oxytocin precursor gene by 33.5 and 13.3-fold in cattle treated with 17β oestradiol and dexamethasone, respectively, in comparison to placebo treated animals. Regulation of gene expression by some myogenic regulatory factors in skeletal muscle was also evaluated in these animal groups, confirming the activity of both growth promoters on this gene. To investigate the use of the oxytocin precursor gene as biomarker for 17β oestradiol and dexamethasone treatment in beef cattle, an absolute quantification of this gene by qPCR was developed. A standard curve was generated and developed with TaqMan® technology and optimal criterion value, sensitivity and specificity of this screening method were established through ROC analysis. This analysis suggested that the up-regulation of oxytocin precursor gene expression in skeletal muscle tissue is a valid marker for detection of illicit 17β oestradiol and/or dexamethasone use in beef cattle. This method may serve as a novel diagnostic tool in the screening phase, and, if introduced in routine testing, may significantly improve overall efficacy and success of the food screening process ordered by state authorities.

Cluster analysis reveals differential transcript profiles associated with resistance training-induced human skeletal muscle hypertrophy

Using genomic microarray analysis, we sought to identify and annotate differences in the pretraining skeletal muscle transcriptomes among human subjects clustered as nonresponders (Non), modest responders (Mod), and extreme responders (Xtr) based on differential magnitudes of myofiber hypertrophy in response to progressive resistance training (RT) (Non-6 μm², Mod 1,111 μm², or Xtr 2,475 μm²). In prior work, we noted differences among clusters in the prevalence of myogenic stem cells prior to and during RT (35), and in the translational signaling responses to the first bout of resistance exercise (30). Here we identified remarkable differences in the pretraining transcript profiles among clusters (8,026 gene transcripts differentially expressed between Xtr and Non, 2,463 between Xtr and Mod, and 1,294 between Mod and Non). Annotated functions and networks of differentially expressed genes suggest Xtr were "primed" to respond to RT through transcriptional regulation, along with a uniquely expressed network of genes involved in skeletal muscle development, while the failed response in Non may have been driven by excessive proinflammatory signaling. Protein follow-up analysis revealed higher basal levels of acetylated histone H3 (K36) in the two responder clusters (Mod, Xtr) compared with Non, and only the responders experienced alterations in the muscle content of select proteins (e.g., α-tubulin, p27(kip)) in response to the first resistance exercise stimulus. Overall, the widely disparate transcriptomes identified prior to RT among the three clusters support the notion that at least some of the interindividual heterogeneity in propensity for RT-induced myofiber hypertrophy is likely predetermined.

Inferring the in vivo cellular program of developing bovine skeletal muscle from expression data

We outline an in vivo cellular program of bovine longissimus muscle development inferred from expression data from 60 days post conception to 3months postnatal. Analytic challenges included changes in cellular composition, ambiguous 'diagnostic' markers of cell type and contrasts between cattle human and mouse myogenesis. Nevertheless, the expression profiles of the myosin isoforms support slow and fast muscle fibres emanating from primary and secondary myogenesis respectively, while expression of the prenatal myosin subunits is down regulated prior to birth. Of the canonical pro-myogenic transcription factors (TF), MYF6 and MYF5 are negatively co-expressed, with MYF6 displaying higher expression in the post-natal samples and MYF5, MYOG, HES6 and PAX7 displaying higher expression in early development. A set of TFs (SIX1, EYA2 and DACH2) considered important in undifferentiated murine cells were equally abundant in differentiated bovine cells. An examination of mammalian regulators of fibre composition, muscle mass and muscle metabolism, underscored the roles of PPARGC1A, TGFβ signalling and the NHR4 Nuclear Hormone Receptors on bovine muscle development. Enriched among the most variably expressed genes from the entire data set were molecules regulating mitochondrial metabolism of carbohydrate (PDK4), fat (UCP3), protein (AGXT2L1) and high energy phosphate (CKMT2). The dramatic increase in the expression of these transcripts, which may enable the peri-natal transition to metabolic independence critical for new-born herbivores, provides surprising evidence for substantial developmental remodelling of muscle mitochondria and reflects changes in nutrient availability. Overall, despite differences in size, metabolism and physiology, the muscle structural subunit expression program appears very similar in ruminants, rodents and humans.

Gene expression phenotypes for lipid metabolism and intramuscular fat in skeletal muscle of cattle

Gene expression phenotypes were evaluated for intramuscular fat (IMF) in bovine skeletal muscle as an alternative to traditional estimates of IMF%. Gene expression data from a time course of LM development in high- and low-marbling Bos taurus cattle crosses were compared to identify genes involved in intramuscular adipocyte lipid metabolism with developmentally similar gene expression profiles. Three sets of genes were identified: triacylglyceride (TAG) synthesis and storage, fatty acid (FA) synthesis, and PPARγ-related genes. In an independent analysis in the LM of 48 Bos indicus cattle, TAG and FA gene sets were enriched in the top 100 genes of which expression was most correlated with IMF% (P = 1.2 × 10(-24) and 3.5 × 10(-9), respectively). In general, genes encoding enzymes involved in the synthesis of FA and TAG in the intramuscular adipocytes were present in the top 100 genes. In B. indicus, effects of a steroid hormone growth promotant (HGP), 2 experimental sites [New South Wales (NSW) and Western Australia (WA)], and 3 tenderness genotypes on the expression levels of genes in the TAG gene set and the correlation of gene expression with IMF% were investigated. Although correlation between expression of 12 individual TAG genes and IMF% was observed in HGP-treated animals in both experimental sites (mean r = 0.43), correlation was not observed for untreated animals at the NSW site (mean r = -0.07, P < 3 × 10(-6)). However, TAG genes showed an average 1.6-fold (P < 0.0004) reduction in expression in the LM of HGP-treated cattle relative to untreated cattle, an effect consistent across both experimental sites. Cattle possessing the favored tenderness calpain 1 and 3 and calpastatin alleles exhibited a greater (P = 0.008) reduction in expression in NSW (1.8-fold reduction, P = 0.0002) compared with WA (1.2-fold reduction, P = 0.03). Tenderness genotype had no impact (P > 0.05) on the correlation of TAG genes with IMF%. In general, the interactions among genotype, treatment and location, and TAG gene set gene expression were consistent with the interactions among the same factors and IMF% detected using 255 animals, of which the 48 in this study were a subset. Thus, the TAG gene set constitutes a gene expression phenotype able to predict effects of different genotypes and treatments on IMF% using much smaller groups than current approaches, even in animals with very low IMF%.

Transcriptomic markers meet the real world: finding diagnostic signatures of corticosteroid treatment in commercial beef samples

Background

The use of growth-promoters in beef cattle, despite the EU ban, remains a frequent practice. The use of transcriptomic markers has already proposed to identify indirect evidence of anabolic hormone treatment. So far, such approach has been tested in experimentally treated animals. Here, for the first time commercial samples were analyzed.

Results

Quantitative determination of Dexamethasone (DEX) residues in the urine collected at the slaughterhouse was performed by Liquid Chromatography-Mass Spectrometry (LC-MS). DNA-microarray technology was used to obtain transcriptomic profiles of skeletal muscle in commercial samples and negative controls. LC-MS confirmed the presence of low level of DEX residues in the urine of the commercial samples suspect for histological classification. Principal Component Analysis (PCA) on microarray data identified two clusters of samples. One cluster included negative controls and a subset of commercial samples, while a second cluster included part of the specimens collected at the slaughterhouse together with positives for corticosteroid treatment based on thymus histology and LC-MS. Functional analysis of the differentially expressed genes (3961) between the two groups provided further evidence that animals clustering with positive samples might have been treated with corticosteroids. These suspect samples could be reliably classified with a specific classification tool (Prediction Analysis of Microarray) using just two genes.

Conclusions

Despite broad variation observed in gene expression profiles, the present study showed that DNA-microarrays can be used to find transcriptomic signatures of putative anabolic treatments and that gene expression markers could represent a useful screening tool.

Beyond differential expression: the quest for causal mutations and effector molecules

High throughput gene expression technologies are a popular choice for researchers seeking molecular or systems-level explanations of biological phenomena. Nevertheless, there has been a groundswell of opinion that these approaches have not lived up to the hype because the interpretation of the data has lagged behind its generation. In our view a major problem has been an over-reliance on isolated lists of differentially expressed (DE) genes which – by simply comparing genes to themselves – have the pitfall of taking molecular information out of context. Numerous scientists have emphasised the need for better context. This can be achieved through holistic measurements of differential connectivity in addition to, or in replacement, of DE. However, many scientists continue to use isolated lists of DE genes as the major source of input data for common readily available analytical tools. Focussing this opinion article on our own research in skeletal muscle, we outline our resolutions to these problems – particularly a universally powerful way of quantifying differential connectivity. With a well designed experiment, it is now possible to use gene expression to identify causal mutations and the other major effector molecules with whom they cooperate, irrespective of whether they themselves are DE. We explain why, for various reasons, no other currently available experimental techniques or quantitative analyses are capable of reaching these conclusions.

The effect of combination treatment with trenbolone acetate and estradiol-17β on skeletal muscle expression and plasma concentrations of oxytocin in sheep

Implantation of trenbolone acetate (TBA) in conjunction with estradiol-17β (E(2)) increases growth, feed conversion efficiency, and carcass leanness in cattle. Our previous study in Brahman steers suggested that the neuropeptide hormone oxytocin (OXT) may be involved in increasing muscle growth after TBA-E(2) treatment. The present study aimed to determine whether OXT mRNA expression in the longissimus muscle (LM) is also up-regulated in TBA-E(2-)implanted wethers as has been found in steers. Real-time quantitative PCR was used to measure the expression of the gene encoding the OXT precursor, three genes with increased expression in the LM muscle of TBA-E(2)-treated steers, MYOD1 (muscle transcription factor), GREB1 (growth regulation by estrogen in breast cancer 1), and WISP2 (Wnt-1 inducible signaling pathway protein 2), and two genes encoding IGF pathway proteins, IGF1, IGFR, in the LM of both untreated and TBA-E(2)-treated wethers. The expression of OXT mRNA in wethers that received the TBA-E(2) treatment was increased ~4.4-fold (P = 0.01). TBA-E(2) treatment also induced a 2.3-fold increase in circulating OXT (P = 0.001). These data, together with the observation that untreated wethers had much higher baseline concentrations of circulating OXT than previously observed in steers, suggest that wethers and steers have quite different OXT hormone systems. TBA-E(2) treatment had no effect on the expression of IGF1, IGFR, and the muscle regulatory gene MYOD1 mRNA levels in wethers (P ≥ 0.15), but there was an increase in the expression of the two growth-related genes, GREB1 (P = 0.001) and WISP2 (P = 0.04). Both genes are common gene targets for both the estrogen and androgen signaling pathways. Consequently, their actions may contribute to the positive interaction between TBA and E(2) on additive improvements on muscle growth.