Muscle fibre size optimisation provides flexibility for energy budgeting in calorie-restricted coho salmon transgenic for growth hormone

The Emerging Role of Long Non-Coding RNAs in Development and Function of Gilthead Sea Bream (Sparus aurata) Fast Skeletal Muscle

Long non-coding RNAs (lncRNAs) are an emerging group of ncRNAs that can modulate gene expression at the transcriptional or translational levels. In the present work, previously published transcriptomic data were used to identify lncRNAs expressed in gilthead sea bream skeletal muscle, and their transcription levels were studied under different physiological conditions. Two hundred and ninety lncRNAs were identified and, based on transcriptomic differences between juveniles and adults, a total of seven lncRNAs showed potential to be important for muscle development. Our data suggest that the downregulation of most of the studied lncRNAs might be linked to increased myoblast proliferation, while their upregulation might be necessary for differentiation. However, with these data, as it is not possible to propose a formal mechanism to explain their effect, bioinformatic analysis suggests two possible mechanisms. First, the lncRNAs may act as sponges of myoblast proliferation inducers microRNAs (miRNAs) such as miR-206, miR-208, and miR-133 (binding energy MEF < -25.0 kcal). Secondly, lncRNA20194 had a strong predicted interaction towards the myod1 mRNA (ndG = -0.17) that, based on the positive correlation between the two genes, might promote its function. Our study represents the first characterization of lncRNAs in gilthead sea bream fast skeletal muscle and provides evidence regarding their involvement in muscle development.

Skeletal muscle fibers count on nuclear numbers for growth

Skeletal muscle cells are noteworthy for their syncytial nature, with each myofiber accumulating hundreds or thousands of nuclei derived from resident muscle stem cells (MuSCs). These nuclei are accrued through cell fusion, which is controlled by the two essential fusogens Myomaker and Myomerger that are transiently expressed within the myogenic lineage. While the absolute requirement of fusion for muscle development has been known for decades, the underlying need for the magnitude of multinucleation in muscle remains mysterious. Possible advantages of multinucleation include the potential it affords for transcriptional diversity within these massive cells, and as a means of increasing DNA content to support optimal cell size and function. In this article, we review recent advances that elucidate the relationship between myonuclear numbers and establishment of myofiber size, and discuss how this new information refines our understanding of the concept of myonuclear domains (MND), the cytoplasmic volumes that each resident myonucleus can support. Finally, we explore the potential consequences and costs of multinucleation and its impacts on myonuclear transcriptional reserve capacity, growth potential, myofiber size regulation, and muscle adaptability. We anticipate this report will not only serve to highlight the latest advances in the basic biology of syncytial muscle cells but also provide information to help design the next generation of therapeutic strategies to maintain muscle mass and function.

Satellite cell division and fiber hypertrophy alternate with new fiber formation during indeterminate muscle growth in juvenile lake sturgeon (Acipenser fulvescens)

Age-dependent changes in muscle fiber size, myonuclear domain volume, fiber-end-terminal configuration, fiber and fish growth, and stem cell or satellite cell (SC) number and proliferation were investigated in developing lake sturgeon (Acipenser fulvescens Rafinesque, 1817) to characterize indeterminate muscle growth during early life. We hypothesized that up to 29 months post hatch (MPH), SC numbers and mitotic activity, the mitotic cycle duration of SCs, fiber morphology, and the volume of cytoplasmic domains around fiber nuclei would change during periods of fiber hypertrophy and hyperplasia. Single-fiber cultures were used in pulse-chase studies of SC division and the Pax7+ SC population. The number of SCs per fiber increased until 17 MPH, peaking as a proportion of fiber nuclei at 3 and 17 MPH. SC cycle time decreased in duration with age after peaks at 3 and 5 MPH. Domain volume was high at 1 and 29 MPH and low from 2 to 6 MPH. Fibers with uniformly tapered ends were most frequent at 4 MPH. Results suggest 3 and 6–17 MPH as intervals for both SC proliferation and fiber hypertrophy, and that fiber growth alternated with new fiber formation (termed fiber hyperplasia) from 4 to 5 MPH and from 17 to 29 MPH. These patterns of cellular dynamics in lake sturgeon muscle growth advance our understanding of indeterminate growth.

Effect of growth rate on transcriptomic responses to immune stimulation in wild-type, domesticated, and GH-transgenic coho salmon

BACKGROUND

Transcriptomic responses to immune stimulation were investigated in coho salmon (Oncorhynchus kisutch) with distinct growth phenotypes. Wild-type fish were contrasted to strains with accelerated growth arising either from selective breeding (i.e. domestication) or genetic modification. Such distinct routes to accelerated growth may have unique implications for relationships and/or trade-offs between growth and immune function.

RESULTS

RNA-Seq was performed on liver and head kidney in four 'growth response groups' injected with polyinosinic-polycytidylic acid (Poly I:C; viral mimic), peptidoglycan (PGN; bacterial mimic) or PBS (control). These groups were: 1) 'W': wild-type, 2) 'TF': growth hormone (GH) transgenic salmon with ~ 3-fold higher growth-rate than W, 3) 'TR': GH transgenic fish ration restricted to possess a growth-rate equal to W, and 4) 'D': domesticated non-transgenic fish showing growth-rate intermediate to W and TF. D and TF showed a higher similarity in transcriptomic response compared to W and TR. Several immune genes showed constitutive expression differences among growth response groups, including perforin 1 and C-C motif chemokine 19-like. Among the affected immune pathways, most were up-regulated by Poly I:C and PGN. In response to PGN, the c-type lectin receptor signalling pathway responded uniquely in TF and TR. In response to stimulation with both immune mimics, TR responded more strongly than other groups. Further, group-specific pathway responses to PGN stimulation included NOD-like receptor signalling in W and platelet activation in TR. TF consistently showed the most attenuated immune response relative to W, and more DEGs were apparent in TR than TF and D relative to W, suggesting that a non-satiating ration coupled with elevated circulating GH levels may cause TR to possess enhanced immune capabilities. Alternatively, TF and D salmon are prevented from acquiring the same level of immune response as TR due to direction of energy to high overall somatic growth. Further study of the effects of ration restriction in growth-modified fishes is warranted.

CONCLUSIONS

These findings improve our understanding of the pleiotropic effects of growth modification on the immunological responses of fish, revealing unique immune pathway responses depending on the mechanism of growth acceleration and nutritional availability.

Growth and survival of Takifugu rubripes larvae cultured under different light conditions

We assessed the effects of light intensity and spectrum on the growth and survival of Takifugu rubripes larvae from 30 to 69 days after hatching. Five lighting regimes were applied using 0.5, 1.5, and 3.0 W m^-2 full spectrum white (W0.5, W1.5, W3.0), 0.5 W m^-2 yellow (Y0.5), and 0.5 W m^-2 blue light (B0.5). At the end of the experiment, body length, wet weight, and specific growth rate from day 0 to day 39 were significantly greater in larvae reared under W3.0 than under B0.5 (P ˂ 0.05). No significant differences were observed among W0.5, W1.5, and W3.0, or among W0.5, Y0.5, and B0.5 (P > 0.05). Survival rate was significantly higher in larvae reared under W1.5 than W0.5 (P ˂ 0.05), but no significant differences were observed among W0.5, Y0.5, and B0.5 (P > 0.05). Additionally, light conditioning did not affect the total thickness of the retina. Although the ratio of the thickness of the retinal pigment epithelium layer/total thickness (TT) was significantly higher in larvae exposed to W3.0 compared with those exposed to other light conditions, and the thickness of the outer nuclear layer/TT was significantly lower in larvae exposed to W3.0 compared with those exposed to W0.5 (P < 0.05), no relationship was confirmed between the structure of the retina and the growth performance of the T. rubripes larvae. Expression patterns of two stress-related and seven growth-related genes were also compared with the biometric parameters investigated in the experimental groups. No significant differences in the aanat1a, crh, ss1, igf1, or igf2 expression were observed among the five treatments. Pomc expression was significantly lower in larvae exposed to W1.5 than the larvae exposed to W0.5, and it was significantly lower in larvae exposed to Y0.5 than in larvae exposed to W0.5 or B0.5 (P < 0.05). Significant differences were also found in the expression of gh, with the highest levels being observed under W3.0, while the lowest levels were observed in B0.5 (P < 0.05). Ghrh expression was significantly higher in W3.0 (P < 0.05). These results should be considered when designing rearing protocols for fugu larvae in aquaculture systems.

Effects of an unprecedented summer heatwave on the growth performance, flesh colour and plasma biochemistry of marine cage-farmed Atlantic salmon (Salmo salar)

Global seawater temperatures are increasing and becoming more variable, with consequences for all marine animals including those in food production systems. In several countries around the world,arming of Atlantic salmon (Salmo salar) occurs towards the upper end of the thermal tolerance window for this species, and marked effects on salmon production during summers have been experienced but never empirically investigated. This project tracked the effects of an extreme summer heatwave on two different cohorts of fish stocked into farm cages either during early winter (EW) or late winter (LW). The farm site experienced an unprecedented high water temperature event, with a peak water temperature of 22.9 °C and 117 days above 18 °C. Fish in both EW and LW cohorts experienced a temperature-induced cessation of voluntary feed intake as well as inefficient osmoregulatory, liver and renal function during high temperature periods. Flesh colour declined primarily in the dorsal and ventral regions of the fillet and secondarily along the midline, with over 20% of fish demonstrated a complete loss of flesh colour during the months of March and April. A return to feeding in autumn occurred faster in some fish and caused a marked bimodal size distribution to appear within both the EW and LW cohorts as autumn progressed. However, the LW cohort returned to feeding at seawater temperatures of 20.2 °C, compared with 18.6 °C for the EW cohort. There was a strong positive relationship between fillet colour recovery and residual condition index (RCI). These findings identified alkaline phosphatase as a potential marker to non-destructively track individual fish for signs of recovery after a thermal stress event, and shed light on the physiological consequences of marine heatwaves on fishes. This study also identified that supporting feed intake or promoting a return to feeding may help mitigate the negative impacts of climate warming on cultured Atlantic salmon.

Recombinant bovine growth hormone (rBGH) enhances somatic growth by regulating the GH-IGF axis in fingerlings of gilthead sea bream (Sparus aurata)

The growth hormone (GH)/insulin-like growth factors (IGFs) endocrine axis is the main growth-regulator system in vertebrates. Some authors have demonstrated the positive effects on growth of a sustained-release formulation of a recombinant bovine GH (rBGH) in different fish species. The aim of this work was to characterize the effects of a single injection of rBGH in fingerlings of gilthead sea bream on growth, GH-IGF axis, and both myogenic and osteogenic processes. Thus, body weight and specific growth rate were significantly increased in rBGH-treated fish respect to control fish at 6weeks post-injection, whereas the hepatosomatic index was decreased and the condition factor and mesenteric fat index were unchanged, altogether indicating enhanced somatic growth. Moreover, rBGH injection increased the plasma IGF-I levels in parallel with a rise of hepatic mRNA from total IGF-I, IGF-Ic and IGF-II, the binding proteins IGFBP-1a and IGFBP-2b, and also the receptors IGF-IRb, GHR-I and GHR-II. In skeletal muscle, the expression of IGF-Ib and GHR-I was significantly increased but that of IGF-IRb was reduced; the mRNA levels of myogenic regulatory factors, proliferation and differentiation markers (PCNA and MHC, respectively), or that of different molecules of the signaling pathway (TOR/AKT) were unaltered. Besides, the growth inhibitor myostatin (MSTN1 and MSTN2) and the hypertrophic marker (MLC2B) expression resulted significantly enhanced, suggesting altogether that the muscle is in a non-proliferative stage of development. Contrarily in bone, although the expression of most molecules of the GH/IGF axis was decreased, the mRNA levels of several osteogenic genes were increased. The histology analysis showed a GH induced lipolytic effect with a clear decrease in the subcutaneous fat layer. Overall, these results reveal that a better growth potential can be achieved on this species and supports the possibility to improve growth and quality through the optimization of its culture conditions.

Essential roles of stat5.1/stat5b in controlling fish somatic growth

Signal transducer and activator of transcription 5b (STAT5b) has been identified as a key downstream mediator of growth hormone (GH) signaling in somatic growth of mammalian. However, the corresponding homologue gene of Stat5b is unknown in fish species. In this study, we generated loss-of-function mutants in stat5.1 and stat5.2, two stat5 homologues existing in zebrafish. In stat5.1-deficient zebrafish, a significant reduction of body length and body weight was detected in the embryos/larvae and adults compared with the wild-type control fish, and sexual size dimorphism in adult zebrafish was also eliminated. However, the stat5.2-deficient zebrafish displayed a normal developmental phenotype during all lifespan. Chromatin immunoprecipitation combined with deep sequencing (ChIP-seq) method was adopted to further investigate the potential transcriptional targets of Stat5 protein and cast much light upon the biological function of Stat5. We identified more than 800 genes as transcriptional targets of Stat5 during zebrafish embryogenesis. KEGG analysis indicated that the Stat5 target gene network is predominantly linked to the metabolic pathways, neuroactive ligand-receptor interaction and JAK-STAT signaling pathways. Further validation studies suggested that Stat5.1 protein could directly regulate the expression of gh1, and stat5.1-mutated zebrafish showed a reduction of gh1 mRNA level. In the present study, stat5.1 was revealed as the corresponding homologue gene of Stat5b in fish species. Additionally, we found a novel molecular interaction between Stat5.1/Stat5b and GH, and unraveled a positive feedback loop Stat5.1-GH-Stat5.1 which is necessary for somatic growth and body development in zebrafish.

Transcriptome profiling in fast versus slow-growing rainbow trout across seasonal gradients

Background

Circannual rhythms in vertebrates can influence a wide variety of physiological processes. Some notable examples include annual reproductive cycles and for poikilotherms, seasonal changes modulating growth. Increasing water temperature elevates growth rates in fishes, but increases in photoperiod regime can have similar influences even at constant temperature. Therefore, in order to understand the dynamics of growth in fish it is important to consider the background influence of photoperiod regime on gene expression differences. This study examined the influence of a declining photoperiod regime (winter solstice) compared to an increasing photoperiod regime (spring equinox) on white muscle transcriptome profiles in fast and slow-growing rainbow trout from a commercial aquaculture strain.

Results

Slow-growing fish could be characterized as possessing transcriptome profiles that conform in many respects to an endurance training regime in humans. They have elevated mitochondrial and cytosolic creatine kinase expression levels and appear to suppress mTOR-signaling as evidenced by elevated TSC2 expression, and they also have elevated p53 levels. Large fish display a physiological repertoire that may be consistent with strength/resistance physiology having elevated cytoskeletal gene component expression and glycogen metabolism cycling along with higher PI3K levels. In many respects small vs. large fish match eccentric vs. concentric muscle expression patterns, respectively. Lipid metabolic genes are also more elevated in larger fish, the most notable being the G0S2 switch gene. M and Z-line sarcomere remodelling appears to be more prevalent in large fish. Twenty-three out of 26 gene families with previously reported significant SNP-based growth differences were detected as having significant expression differences.

Conclusions

Larger fish display a broader array of genes showing higher expression, and their profiles are more similar to those observed in December lot fish (i.e., an accelerated growth period). Conversely, small fish display gene profiles more similar to seasonal growth decline phases (i.e., September lot fish). Overall, seasonal timing was coupled to greater differences in gene expression compared to differences associated with fish size.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2363-5) contains supplementary material, which is available to authorized users.

A feedback regulatory loop involving p53/miR-200 and growth hormone endocrine axis controls embryo size of zebrafish

In vertebrates, growth hormone/insulin-like growth factor (GH/IGF) axis signaling plays a critical role in regulating somatic growth. Understanding the direct upstream regulators of GH/IGF axis remains a major challenge. Our studies of the zebrafish reveal that the conserved miR-200 family members are critical regulators of embryo size by targeting several GH/IGF axis genes, including GH, GHRa, GHRb and IGF2a. Overexpression of miR-200s led to cell cycle arrest in the G1 phase and induced apoptotic responses during embryo development, thereby inhibiting somatic growth of zebrafish embryos. Intriguingly, GH induced expression of both p53 and miR-200s, and miR-200s is a potential p53 transcriptional target, thus forming a negative feedback loop. Significantly, the up-regulation of miR-200s associated with GH activation is abolished in embryos with p53 mutation. By integrating these studies, we conclude that p53/miR-200 and GH/IGF signaling pathway form a negative regulatory loop to control embryo size, that provide critical insights into the long-standing puzzle of how body growth is determined during early development of teleosts.

RNAseq analysis of fast skeletal muscle in restriction-fed transgenic coho salmon (Oncorhynchus kisutch): an experimental model uncoupling the growth hormone and nutritional signals regulating growth

BACKGROUND

Coho salmon (Oncorhynchus kisutch) transgenic for growth hormone (Gh) express Gh in multiple tissues which results in increased appetite and continuous high growth with satiation feeding. Restricting Gh-transgenics to the same lower ration (TR) as wild-type fish (WT) results in similar growth, but with the recruitment of fewer, larger diameter, muscle skeletal fibres to reach a given body size. In order to better understand the genetic mechanisms behind these different patterns of muscle growth and to investigate how the decoupling of Gh and nutritional signals affects gene regulation we used RNA-seq to compare the fast skeletal muscle transcriptome in TR and WT coho salmon.

RESULTS

Illumina sequencing of individually barcoded libraries from 6 WT and 6 TR coho salmon yielded 704,550,985 paired end reads which were used to construct 323,115 contigs containing 19,093 unique genes of which >10,000 contained >90 % of the coding sequence. Transcripts coding for 31 genes required for myoblast fusion were identified with 22 significantly downregulated in TR relative to WT fish, including 10 (vaspa, cdh15, graf1, crk, crkl, dock1, trio, plekho1a, cdc42a and dock5) associated with signaling through the cell surface protein cadherin. Nineteen out of 44 (43 %) translation initiation factors and 14 of 47 (30 %) protein chaperones were upregulated in TR relative to WT fish.

CONCLUSIONS

TR coho salmon showed increased growth hormone transcripts and gene expression associated with protein synthesis and folding than WT fish even though net rates of protein accretion were similar. The uncoupling of Gh and amino acid signals likely results in additional costs of transcription associated with protein turnover in TR fish. The predicted reduction in the ionic costs of homeostasis in TR fish associated with increased fibre size were shown to involve multiple pathways regulating myotube fusion, particularly cadherin signaling.

Developmental programming: the role of growth hormone

Developmental programming of the fetus has consequences for physiologic responses in the offspring as an adult and, more recently, is implicated in the expression of altered phenotypes of future generations. Some phenotypes, such as fertility, bone strength, and adiposity are highly relevant to food animal production and in utero factors that impinge on those traits are vital to understand. A key systemic regulatory hormone is growth hormone (GH), which has a developmental role in virtually all tissues and organs. This review catalogs the impact of GH on tissue programming and how perturbations early in development influence GH function.