Integration mechanisms of transgenes and population fitness of GH transgenic fish

Decoding the fish genome opens a new era in important trait research and molecular breeding in China

Aquaculture represents the fastest-growing global food production sector, as it has become an essential component of the global food supply. China has the world's largest aquaculture industry in terms of production volume. However, the sustainable development of fish culture is hindered by several concerns, including germplasm degradation and disease outbreaks. The practice of genomic breeding, which relies heavily on genome information and genotypephenotype relationships, has significant potential for increasing the efficiency of aquaculture production. In 2014, the completion of the genome sequencing and annotation of the Chinese tongue sole signified the beginning of the fish genomics era in China. Since then, domestic researchers have made dramatic progress in functional genomic studies. To date, the genomes of more than 60 species of fish in China have been assembled and annotated. Based on these reference genomes, evolutionary, comparative, and functional genomic studies have revolutionized our understanding of a wide range of biologically and economically important traits of fishes, including growth and development, sex determination, disease resistance, metamorphosis, and pigmentation. Furthermore, genomic tools and breeding techniques such as SNP arrays, genomic selection, and genome editing have greatly accelerated genetic improvement through the incorporation of functional genomic information into breeding activities. This review aims to summarize the current status, advances, and perspectives of the genome resources, genomic study of important traits, and genomic breeding techniques of fish in China. The review will provide aquaculture researchers, fish breeders, and farmers with updated information concerning fish genomic research and breeding technology. The summary will help to promote the genetic improvement of production traits and thus will support the sustainable development of fish aquaculture.

A 90-Day Subchronic Toxicity Study of Consumption of GH-Transgenic Triploid Carp in Wistar Rats

Genetic modification (GM) offers an alternative strategy to conventional animal breeding. The present study was carried out to investigate the potential health effects of the consumption of growth hormone-transgenic triploid carp (GH-ttc) through a 90-day subchronic rodent feeding study. Wistar rats (n = 10/sex/group) were given formulated diets containing GH-ttc or non-GM carp at an incorporated rate of 2.5%, 5%, or 10% (w/w) for 90 days. An additional control group of rats (n = 10/sex/group) was fed a basic rodent diet. During the 90-day study, clinical observation, ophthalmic examination, body weight, and food intake were evaluated. At the end of the study, rats were killed, and the hematology, serum chemistry, urine test, necropsy, and histopathology were assessed. Compared with the non-GM carp and the basic control groups, no biologically significant differences were observed on clinical signs of toxicity, body weights, food intake, hematology, serum chemistry, urinalysis, organ weight, and histopathology on selected organs for the GH-ttc group. The results of this 90-day subchronic feeding study indicated that, at the dose level used in this study, consumption of GH-ttc showed no subchronic toxicity to Wistar rats.

Efficient Gene Transfer and Gene Editing in Sterlet (Acipenser ruthenus)

The sturgeon (Acipenseriformes) is an important farmed species because of its economical value. However, neither gene transfer nor gene editing techniques have been established in sturgeon for molecular breeding and gene functional study until now. In this study, we accomplished gene transfer and gene editing in sterlet (Acipenser ruthenus), which has the shortest sexual maturation period of sturgeons. The plasmid encoding enhanced green fluorescent protein (EGFP) was transferred into the embryos of sterlet at injection concentration of 100 ng/μL, under which condition high survival rate and gene transfer rate could be achieved. Subsequently, exogenous EGFP was efficiently disrupted by transcription activator-like effector nucleases (TALENs) or clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 nuclease/guide RNA (gRNA), with injection concentrations of 300 ng/μL TALENs, or 100 ng/μL Cas9 nuclease and 30 ng/μL gRNA, respectively, under which condition high survival rate and gene mutation rate could be achieved. Finally, the endogenous gene no tail in sterlet was successfully mutated by Cas9 nuclease/gRNA. We observed the CRISPR-induced no tail mutation, at a high efficiency with the mutant P0 embryos displaying the expected phenotype of bent spine and twisted tail.

The Socialist Origins of Artificial Carp Reproduction in Maoist China

The Maoist era has often been portrayed as a hindrance to China’s biotechnological development due to Lysenko doctrine and the communist government’s animosity to basic academic research. Yet some of China’s most developed sectors in biotechnology have been made possible by socialist enterprises in agriculture and science under Mao. One such example is China’s world-leading aquaculture biotechnology and genetic research on Asian carp. Although some associated China’s success in the area with the booming Asian market and a globalised biotech industry, the field’s advancement has been deeply rooted in earlier socialist history in reforming aquaculture and science. This article takes one essential technology used by biotech and aquaculture industries–the hormone-aided method in artificial carp reproduction–as a major case. By tracing the political, scientific and sociocultural lineages that made its invention and dissemination possible, this article unpacks the complex local and historical underpinning that defies prevalent understanding about the method as simply a variation of biotechnology’s global form. Particularly, the initial invention of the method was catalysed not only by state economic concerns but also by a socialist understanding of fishery and Maoist attempts to remold scientists. The two successful breakthroughs described in the article demonstrate two ways that scientists and technicians of different social and professional standings have appropriated available scientific and political resources to achieve personal and institutional goals. The dissemination of the method was further cemented through mass involvement during the Cultural Revolution. By delineating the concrete processes that have ‘assembled’ and maintained the artificial carp propagation method, the article contrasts its entanglement with the socialist regime then with the way the method has become decontextualised in its current use.

Regulation of feeding behavior and food intake by appetite-regulating peptides in wild-type and growth hormone-transgenic coho salmon

Survival, competition, growth and reproductive success in fishes are highly dependent on food intake, food availability and feeding behavior and are all influenced by a complex set of metabolic and neuroendocrine mechanisms. Overexpression of growth hormone (GH) in transgenic fish can result in greatly enhanced growth rates, feed conversion, feeding motivation and food intake. The objectives of this study were to compare seasonal feeding behavior of non-transgenic wild-type (NT) and GH-transgenic (T) coho salmon (Oncorhynchus kisutch), and to examine the effects of intraperitoneal injections of the appetite-regulating peptides cholecystokinin (CCK-8), bombesin (BBS), glucagon-like peptide-1 (GLP-1), and alpha-melanocyte-stimulating hormone (α-MSH) on feeding behavior. T salmon fed consistently across all seasons, whereas NT dramatically reduced their food intake in winter, indicating the seasonal regulation of appetite can be altered by overexpression of GH in T fish. Intraperitoneal injections of CCK-8 and BBS caused a significant and rapid decrease in food intake for both genotypes. Treatment with either GLP-1 or α-MSH resulted in a significant suppression of food intake for NT but had no effect in T coho salmon. The differential response of T and NT fish to α-MSH is consistent with the melanocortin-4 receptor system being a significant pathway by which GH acts to stimulate appetite. Taken together, these results suggest that chronically increased levels of GH alter feeding regulatory pathways to different extents for individual peptides, and that altered feeding behavior in transgenic coho salmon may arise, in part, from changes in sensitivity to peripheral appetite-regulating signals.

A controllable on-off strategy for the reproductive containment of fish

A major impediment to the commercialization and cultivation of transgenic fish is the potential ecological risks they pose to natural environments: a problem that could be solved by the production of sterile transgenic fish. Here, we have developed an on-off reproductive containment strategy for fish that renders the offspring sterile but leaves their parents fertile. TG1 (Tol2-CMV-GFP-pA-CMV-gal4-pA-Tol2) and TG2 (Tol2-CMV-RFP-pA-5 × UAS-as/dnd-pA-Tol2) zebrafish lines were established using a GAL4/UAS system. While the parental lines remained fertile, in the hybrid offspring, GAL4 induced 5 × UAS to drive the transcription of antisense dnd, which significantly down-regulated endogenous dnd expression. This disrupted the migration of primordial germ cells (PGCs), led to their apoptosis, and resulted in few or no PGCs migrating to the genital ridge. This process induced sterility or reduced fertility in adult fish. This on-off strategy is a potentially effective means of generating sterile fish for commercialization while retaining fertility in brood stocks, and offers a novel method to mitigate the ecological risks of fish introductions.

Effects of growth hormone over-expression on reproduction in the common carp Cyprinus carpio L

To study the complex interaction between growth and reproduction we have established lines of transgenic common carp (Cyprinus carpio) carrying a grass carp (Ctenopharyngodon idellus) growth hormone (GH) transgene. The GH-transgenic fish showed delayed gonadal development compared with non-transgenic common carp. To gain a better understanding of the phenomenon, we studied body growth, gonad development, changes of reproduction related genes and hormones of GH-transgenic common carp for 2years. Over-expression of GH elevated peripheral gh transcription, serum GH levels, and inhibited endogenous GH expression in the pituitary. Hormone analyses indicated that GH-transgenic common carp had reduced pituitary and serum level of luteinizing hormone (LH). Among the tested genes, pituitary lhβ was inhibited in GH-transgenic fish. Further analyses in vitro showed that GH inhibited lhβ expression. Localization of ghr with LH indicates the possibility of direct regulation of GH on gonadotrophs. We also found that GH-transgenic common carp had reduced pituitary sensitivity to stimulation by co-treatments with a salmon gonadotropin-releasing hormone (GnRH) agonist and a dopamine antagonist. Together these results suggest that the main cause of delayed reproductive development in GH transgenic common carp is reduced LH production and release.

Risk-taking behaviour may explain high predation mortality of GH-transgenic common carp Cyprinus carpio

The competitive ability and habitat selection of juvenile all-fish GH-transgenic common carp Cyprinus carpio and their size-matched non-transgenic conspecifics, in the absence and presence of predation risk, under different food distributions, were compared. Unequal-competitor ideal-free-distribution analysis showed that a larger proportion of transgenic C. carpio fed within the system, although they were not overrepresented at a higher-quantity food source. Moreover, the analysis showed that transgenic C. carpio maintained a faster growth rate, and were more willing to risk exposure to a predator when foraging, thereby supporting the hypothesis that predation selects against maximal growth rates by removing individuals that display increased foraging effort. Without compensatory behaviours that could mitigate the effects of predation risk, the escaped or released transgenic C. carpio with high-gain and high-risk performance would grow well but probably suffer high predation mortality in nature.

Increased food intake in growth hormone-transgenic common carp (Cyprinus carpio L.) may be mediated by upregulating Agouti-related protein (AgRP)

In fish, food intake and feeding behavior are crucial for survival, competition, growth and reproduction. Growth hormone (GH)-transgenic common carp exhibit an enhanced growth rate, increased food intake and higher feed conversion rate. However, the underlying molecular mechanisms of feeding regulation in GH-transgenic (TG) fish are not clear. In this study, we observed feeding behavior of TG and non-transgenic (NT) common carp, and analyzed the mRNA expression levels of NPY, AgRP I, orexin, POMC, CCK, and CART I in the hypothalamus and telencephalon after behavioral observation. We detected similar gene expression levels in the hypothalamus of TG and NT common carp, which had been cultured in the field at the same age. Furthermore, we tested the effects of GH on hypothalamus fragments in vitro to confirm our findings. We demonstrated that TG common carp displayed increased food intake and reduced food consumption time, which were associated with a marked increase in hypothalamic AgRP I mRNA expression. Our results suggest that elevated GH levels may influence food intake and feeding behavior by upregulating the hypothalamic orexigenic factor AgRP I in GH-transgenic common carp.

[Progress in transgenic fish techniques and application]

Transgenic technique provides a new way for fish breeding. Stable lines of growth hormone gene transfer carps, salmon and tilapia, as well as fluorescence protein gene transfer zebra fish and white cloud mountain minnow have been produced. The fast growth characteristic of GH gene transgenic fish will be of great importance to promote aquaculture production and economic efficiency. This paper summarized the progress in transgenic fish research and ecological assessments. Microinjection is still the most common used method, but often resulted in multi-site and multi-copies integration. Co-injection of transposon or meganuclease will greatly improve the efficiency of gene transfer and integration. "All fish" gene or "auto gene" should be considered to produce transgenic fish in order to eliminate misgiving on food safety and to benefit expression of the transferred gene. Environmental risk is the biggest obstacle for transgenic fish to be commercially applied. Data indicates that transgenic fish have inferior fitness compared with the traditional domestic fish. However, be-cause of the genotype-by-environment effects, it is difficult to extrapolate simple phenotypes to the complex ecological interactions that occur in nature based on the ecological consequences of the transgenic fish determined in the laboratory. It is critical to establish highly naturalized environments for acquiring reliable data that can be used to evaluate the environ-mental risk. Efficacious physical and biological containment strategies remain to be crucial approaches to ensure the safe application of transgenic fish technology.