Somatotropic axis genes are expressed before pituitary onset during zebrafish and sea bass development

Thyroid disruption and growth inhibition of zebrafish embryos/larvae by phenanthrene treatment at environmentally relevant concentrations

Phenanthrene induces reproductive and developmental toxicity in fish, but whether it can disrupt the thyroid hormone balance and inhibit growth had not been determined to date. In this study, zebrafish embryos were exposed to phenanthrene (0, 0.1, 1, 10 and 100 μg/L) for 7 days. The results of this experiment demonstrated that phenanthrene induced thyroid disruption and growth inhibition in zebrafish larvae. Phenanthrene significantly decreased the concentration of l-thyroxine (T4) but increased that of 3,5,3'-l-triiodothyronine (T3). The expression of genes related to the hypothalamic-pituitary-thyroid (HPT) axis was altered in zebrafish larvae exposed to phenanthrene. Moreover, phenanthrene exposure significantly increased the malformation rate and significantly reduced the survival rate and the body length of zebrafish larvae. Furthermore, phenanthrene significantly decreased the concentrations of growth hormone (GH) and insulin-like growth factor-1 (IGF-1). Changes observed in gene expression patterns further support the hypothesis that these effects may be related to alterations along the GH/IGF-1 axis. In conclusion, our study indicated that exposure to phenanthrene at concentrations as low as 0.1 μg/L resulted in thyroid disruption and growth inhibition in zebrafish larvae. Therefore, the estimation of phenanthrene levels in the aquatic environment needs to be revisited.

Sex steroid dynamics and mRNA transcript profiles of growth- and development-related genes during embryogenesis following induced follicular maturation in European eel

Hormones and mRNA transcripts of maternal origin deposited in the egg may affect early embryonic development in oviparous species. These hormones include steroids, such as estradiol-17β (E2), testosterone (T), 11-ketotestosterone (11-kt), 17α,20ß-dihydroxy-4-pregnen-3-one (DHP), and cortisol, which also play an important role in fish reproduction. In European eel, Anguilla anguilla, which does not reproduce naturally in captivity, vitellogenesis in female broodstock is commonly induced by administration of salmon or carp pituitary extract (PE) as an exogenous source of gonadotropins, while follicular maturation is stimulated by a priming dose of PE followed by provision of DHP as a maturation inducing hormone. In this regard, the main purpose of the present study was to evaluate effects of induced follicular maturation on reproductive success in European eel, focusing on maternal transfer and dynamics of steroids and mRNA transcripts of growth- and development-related genes throughout embryogenesis. The results showed that maternal blood plasma concentrations of E2, T and DHP were reflected in the unfertilized eggs. Moreover, a negative relationship between concentrations of E2 and DHP in eggs and embryos and quality parameters measured as fertilization success, cleavage abnormalities, embryonic survival, and hatch success was found. Concomitant mRNA transcript abundance analysis including genes involved in stress response (hsp70, hsp90), somatotropic axis (gh, igf1, igf2a, igf2b), lipid (cpt1a, cpt1b, pigf5) and thyroid metabolism (dio1, dio2, dio3, thrαb, thrβa, thrβb) varied among unfertilized egg batches. For the majority of genes, mRNA abundance increased during the maternal-to-zygotic transition in connection to activation of the transcription of the embryos own genome. mRNA abundance of dio1, cpt1a and cpt1b throughout embryogenesis was related to embryonic developmental competence. Notably, mRNA abundance of dio3 was positively associated with E2 concentrations, while the mRNA abundance of thrαb was negatively related to T concentrations in the unfertilized eggs, which may suggest an interaction between the thyroid and steroid hormone systems. Altogether, maternal plasma concentrations of E2 and DHP were reflected in the eggs, with high concentrations of these steroids in the eggs being negatively associated with embryonic developmental competence. Additionally, high transcript levels of two of the investigated genes (dio1, cpt1b) were positively associated with embryonic developmental competence. This study reveals maternal transfer of steroids and mRNA transcripts to the eggs, which may be significant contributors to the variability in embryonic survival observed in European eel captive reproduction.

Transcriptomic profiling of Gh/Igf system reveals a prompted tissue-specific differentiation and novel hypoxia responsive genes in gilthead sea bream

A customized PCR-array was used for the simultaneous gene expression of the Gh/Igf system and related markers of muscle growth, and lipid and energy metabolism during early life stages of gilthead sea bream (60–127 days posthatching). Also, transcriptional reprogramming by mild hypoxia was assessed in fingerling fish with different history trajectories on O₂ availability during the same time window. In normoxic fish, the expression of almost all the genes in the array varied over time with a prompted liver and muscle tissue-specific differentiation, which also revealed temporal changes in the relative expression of markers of the full gilthead sea bream repertoire of Gh receptors, Igfs and Igf-binding proteins. Results supported a different contribution through development of ghr and igf subtypes on the type of action of GH via systemic or direct effects at the local tissue level. This was extensive to Igfbp1/2/4 and Igfbp3/5/6 clades that clearly evolved through development as hepatic and muscle Igfbp subtypes, respectively. This trade-off is however very plastic to cope changes in the environment, and ghr1 and igfbp1/3/4/5 emerged as hypoxic imprinting genes during critical early developmental windows leading to recognize individuals with different history trajectories of oxygen availability and metabolic capabilities later in life.

Insights into early ontogenesis: characterization of stress and development key genes of pikeperch (Sander lucioperca) in vivo and in vitro

There are still numerous difficulties in the successful farming of pikeperch in the anthropogenic environment of various aquaculture systems, especially during early developmental steps in the hatchery. To investigate the physiological processes involved on the molecular level, we determined the basal expression patterns of 21 genes involved in stress and immune responses and early ontogenesis of pikeperch between 0 and 175 days post hatch (dph). Their transcription patterns most likely reflect the challenges of growth and feed conversion. The gene coding for apolipoprotein A (APOE) was strongly expressed at 0 dph, indicating its importance for yolk sac utilization. Genes encoding bone morphogenetic proteins 4 and 7 (BMP4, BMP7), creatine kinase M (CKM), and SRY-box transcription factor 9 (SOX9) were highly abundant during the peak phases of morphological changes and acclimatization processes at 4-18 dph. The high expression of genes coding for peroxisome proliferator-activated receptors alpha and delta (PPARA, PPARD) at 121 and 175 dph, respectively, suggests their importance during this strong growth phase of juvenile stages. As an alternative experimental model to replace further in vivo investigations of ontogenetically important processes, we initiated the first approach towards a long-lasting primary cell culture from whole pikeperch embryos. The present study provides a set of possible biomarkers to support the monitoring of pikeperch farming and provides a first basis for the establishment of a suitable cell model of this emerging aquaculture species.

Chlormequat chloride promotes rat embryonic growth and GH-IGF-1 axis

Chlormequat chloride, a plant growth regulator, is widely applied in agriculture because it can promote sturdier growth of the crops. In this research, we found that rat embryo growth on GD11 was inhibited in vitro at 50 μg/ml but promoted in vivo at 75 mg/kg.bw by maternal oral exposure. Therefore, the concentrations of chlormequat chloride in the sera of the pregnant rats on gestation day (GD)11 were determined by a high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) test to be 1.94 ± 0.023 μg/ml, 3.84 ± 0.080 μg/ml, and 7.08 ± 0.11 μg/ml, respectively, when the pregnant rats were orally exposed to chlormequat chloride at 75, 137.5, and 200 mg/kg.bw. Hence, we performed WEC tests again and confirmed that the rat embryo growth in vitro was promoted by chlormequat chloride at 5 μg/mL. The embryonic growth hormone (GH) and insulin-like growth factor 1 (IGF-1) levels were increased by chlormequat chloride both in vitro and in vivo compared with the control ones. We concluded that chlormequat chloride could elevate GH and IGF-1 levels in embryos and promote embryonic growth both in vitro and in vivo.

Early Developmental Stress Affects Subsequent Gene Expression Response to an Acute Stress in Atlantic Salmon: An Approach for Creating Robust Fish for Aquaculture?

Stress during early life has potential to program and alter the response to stressful events and metabolism in later life. Repeated short exposure of Atlantic salmon to cold water and air during embryonic (E), post-hatch (PH) or both phases of development (EPH) has been shown to alter the methylome and transcriptome and to affect growth performance during later life compared to untreated controls (CO). The aim of this study was to investigate how the transcriptome of these fish responds to subsequent acute stress at the start feeding stage, and to describe methylation differences that might steer these changes. EPH treated fish showed the strongest down-regulation of corticotropin releasing factor 1, up-regulation of glucocorticoid receptor and 3-oxo-5-alpha-steroid 4-dehydrogenase 2 gene expression and a suppressed cortisol response 3 hr after the acute stress, differences that could influence hormesis and be affecting how EPH fish cope and recover from the stress event. Growth hormone 2 and insulin-like growth factor 1 were more strongly down-regulated following acute stress in EPH treated fish relative to E, PH and CO fish. This indicates switching away from growth toward coping with stress following stressful events in EPH fish. Genes implicated in immune function such as major histocompatibility class 1A, T-cell receptor and toll-like receptor also responded to acute stress differently in EPH treated fish, indicating that repeated stresses during early life may affect robustness. Differential DNA methylation was detected in regions mapping <500 bases from genes differentially responding to acute stress suggesting the involvement of epigenetic mechanisms. Stress treatments applied during early development therefore have potential as a husbandry tool for boosting the productivity of aquaculture by affecting how fish respond to stresses at critical stages of production.

Maternal mRNA input of growth and stress-response-related genes in cichlids in relation to egg size and trophic specialization

BACKGROUND

Egg size represents an important form of maternal effect determined by a complex interplay of long-term adaptation and short-term plasticity balancing egg size with brood size. Haplochromine cichlids are maternal mouthbrooders showing differential parental investment in different species, manifested in great variation in egg size, brood size and duration of maternal care. Little is known about maternally determined molecular characters of eggs in fishes and their relation to egg size and trophic specialization. Here we investigate maternal mRNA inputs of selected growth- and stress-related genes in eggs of mouthbrooding cichlid fishes adapted to different trophic niches from Lake Tanganyika, Lake Malawi, Lake Victoria and compare them to their riverine allies.

RESULTS

We first identified two reference genes, atf7ip and mid1ip1, to be suitable for cross-species quantification of mRNA abundance via qRT-PCR in the cichlid eggs. Using these reference genes, we found substantial variation in maternal mRNA input for a set of candidate genes related to growth and stress response across species and lakes. We observed negative correlation of mRNA abundance between two of growth hormone receptor paralogs (ghr1 and ghr2) across all haplochromine cichlid species which also differentiate the species in the two younger lakes, Malawi and Lake Victoria, from those in Lake Tanganyika and ancestral riverine species. Furthermore, we found correlations between egg size and maternal mRNA abundance of two growth-related genes igf2 and ghr2 across the haplochromine cichlids as well as distinct clustering of the species based on their trophic specialization using maternal mRNA abundance of five genes (ghr1, ghr2, igf2, gr and sgk1).

CONCLUSIONS

These findings indicate that variations in egg size in closely related cichlid species can be linked to differences in maternal RNA deposition of key growth-related genes. In addition, the cichlid species with contrasting trophic specialization deposit different levels of maternal mRNAs in their eggs for particular growth-related genes; however, it is unclear whether such differences contribute to differential morphogenesis at later stages of development. Our results provide first insights into this aspect of gene activation, as a basis for future studies targeting their role during ecomorphological specialization and adaptive radiation.

Somatotropic Axis Regulation Unravels the Differential Effects of Nutritional and Environmental Factors in Growth Performance of Marine Farmed Fishes

The Gh/Prl/Sl family has evolved differentially through evolution, resulting in varying relationships between the somatotropic axis and growth rates within and across fish species. This is due to a wide range of endogenous and exogenous factors that make this association variable throughout season and life cycle, and the present minireview aims to better define the nutritional and environmental regulation of the endocrine growth cascade over precisely defined groups of fishes, focusing on Mediterranean farmed fishes. As a result, circulating Gh and Igf-i are revitalized as reliable growth markers, with a close association with growth rates of gilthead sea bream juveniles with deficiency signs in both macro- or micro-nutrients. This, together with other regulated responses, promotes the use of Gh and Igf-i as key performance indicators of growth, aerobic scope, and nutritional condition in gilthead sea bream. Moreover, the sirtuin-energy sensors might modulate the growth-promoting action of somatotropic axis. In this scenario, transcripts of igf-i and gh receptors mirror changes in plasma Gh and Igf-i levels, with the ghr-i/ghr-ii expression ratio mostly unaltered over season. However, this ratio is nutritionally regulated, and enriched plant-based diets or diets with specific nutrient deficiencies downregulate hepatic ghr-i, decreasing the ghr-i/ghr-ii ratio. The same trend, due to a ghr-ii increase, is found in skeletal muscle, whereas impaired growth during overwintering is related to increase in the ghr-i/ghr-ii and igf-ii/igf-i ratios in liver and skeletal muscle, respectively. Overall, expression of insulin receptors and igf receptors is less regulated, though the expression quotient is especially high in the liver and muscle of sea bream. Nutritional and environmental regulation of the full Igf binding protein 1-6 repertoire remains to be understood. However, tissue-specific expression profiling highlights an enhanced and nutritionally regulated expression of the igfbp-1/-2/-4 clade in liver, whereas the igfbp-3/-5/-6 clade is overexpressed and regulated in skeletal muscle. The somatotropic axis is, therefore, highly informative of a wide-range of growth-disturbing and stressful stimuli, and multivariate analysis supports its use as a reliable toolset for the assessment of growth potentiality and nutrient deficiencies and requirements, especially in combination with selected panels of other nutritionally regulated metabolic biomarkers.

Temperature effects on gene expression and morphological development of European eel, Anguilla anguilla larvae

Temperature is important for optimization of rearing conditions in aquaculture, especially during the critical early life history stages of fish. Here, we experimentally investigated the impact of temperature (16, 18, 20, 22 and 24°C) on thermally induced phenotypic variability, from larval hatch to first-feeding, and the linked expression of targeted genes [heat shock proteins (hsp), growth hormone (gh) and insulin-like growth factors (igf)] associated to larval performance of European eel, Anguilla anguilla. Temperature effects on larval morphology and gene expression were investigated throughout early larval development (in real time from 0 to 18 days post hatch) and at specific developmental stages (hatch, jaw/teeth formation, and first-feeding). Results showed that hatch success, yolk utilization efficiency, survival, deformities, yolk utilization, and growth rates were all significantly affected by temperature. In real time, increasing temperature from 16 to 22°C accelerated larval development, while larval gene expression patterns (hsp70, hsp90, gh and igf-1) were delayed at cold temperatures (16°C) or accelerated at warm temperatures (20–22°C). All targeted genes (hsp70, hsp90, gh, igf-1, igf-2a, igf-2b) were differentially expressed during larval development. Moreover, expression of gh was highest at 16°C during the jaw/teeth formation, and the first-feeding developmental stages, while expression of hsp90 was highest at 22°C, suggesting thermal stress. Furthermore, 24°C was shown to be deleterious (resulting in 100% mortality), while 16°C and 22°C (~50 and 90% deformities respectively) represent the lower and upper thermal tolerance limits. In conclusion, the high survival, lowest incidence of deformities at hatch, high yolk utilization efficiency, high gh and low hsp expression, suggest 18°C as the optimal temperature for offspring of European eel. Furthermore, our results suggest that the still enigmatic early life history stages of European eel may inhabit the deeper layer of the Sargasso Sea and indicate vulnerability of this critically endangered species to increasing ocean temperature.

Transcriptomics of mRNA and egg quality in farmed fish: Some recent developments and future directions

Maternal mRNA transcripts deposited in growing oocytes regulate early development and are under intensive investigation as determinants of egg quality. The research has evolved from single gene studies to microarray and now RNA-Seq analyses in which mRNA expression by virtually every gene can be assessed and related to gamete quality. Such studies have mainly focused on genes changing two- to several-fold in expression between biological states, and have identified scores of candidate genes and a few gene networks whose functioning is related to successful development. However, ever-increasing yields of information from high throughput methods for detecting transcript abundance have far outpaced progress in methods for analyzing the massive quantities of gene expression data, and especially for meaningful relation of whole transcriptome profiles to gamete quality. We have developed a new approach to this problem employing artificial neural networks and supervised machine learning with other novel bioinformatics procedures to discover a previously unknown level of ovarian transcriptome function at which minute changes in expression of a few hundred genes is highly predictive of egg quality. In this paper, we briefly review the progress in transcriptomics of fish egg quality and discuss some future directions for this field of study.

Microcystin-LR exposure to adult zebrafish (Danio rerio) leads to growth inhibition and immune dysfunction in F1 offspring, a parental transmission effect of toxicity

Microcystins (MCs) are algal toxins produced intracellularly within the cyanobacteria cells. MCs exposure exerts great harm to the reproductive system of fish and deteriorates the quality of eggs and sperms, and has further adverse effects on early developmental stages of fish. Whether the MC toxicity can be parentally transmitted to offspring, even though the embryos and larvae are free of MC exposure? In the present study, adult zebrafish were continuously exposed to MC-LR (with dose of 1, 5 and 20 μg/L) for 30 days. After MC-LR exposure, fertilized eggs were collected and the following F1 generation was reared in water containing no MC-LR until 60 days post fertilization (dpf). In F1 offspring, both body weight and body length were evidently dropped. Some growth and immune related genes were detected using the real-time PCR. The transcriptional levels of these genes significantly decreased in F1 offspring of zebrafish whose parents were treated with 5 and 20 μg/L MC-LR. The activities of some antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) significantly dropped in 5 and 20 μg/L MC-LR groups, and the malondialdehyde (MDA) levels markedly increased in all the three treatment groups. Furthermore, distinct pathological changes in liver were observed in F1 zebrafish. Our findings show that the MC-LR exposure to parental zebrafish results in liver damage and evidently influences the growth and immune function in F1 offspring. We consider this damage as a parental transmission effect of microcystin toxicity. Further mechanism studies are necessary to elucidate this transmission effect.

Extrapituitary growth hormone and growth?

While growth hormone (GH) is obligatory for postnatal growth, it is not required for a number of growth-without-GH syndromes, such as early embryonic or fetal growth. Instead, these syndromes are thought to be dependent upon local growth factors, rather than pituitary GH. The GH gene is, however, also expressed in many extrapituitary tissues, particularly during early development and extrapituitary GH may be one of the local growth factors responsible for embryonic or fetal growth. Moreover, as the expression of the GH receptor (GHR) gene mirrors that of GH in extrapituitary tissues the actions of GH in early development are likely to be mediated by local autocrine or paracrine mechanisms, especially as extrapituitary GH expression occurs prior to the ontogeny of pituitary somatotrophs or the appearance of GH in the circulation. The extrapituitary expression of pituitary somatotrophs or the appearance of GH in the circulation. The extrapituitary expression of GH in embryos has also been shown to be of functional relevance in a number of species, since the immunoneutralization of endogenous GH or the blockade of GH production is accompanied by growth impairment or cellular apoptosis. The extrapituitary expression of the GH gene also persists in some central and peripheral tissues postnatally, which may reflect its continued functional importance and physiological or pathophysiological significance. The expression and functional relevance of extrapituitary GH, particularly during embryonic growth, is the focus of this brief review.