Embryonic stem cells isolated from Atlantic cod (Gadus morhua) and the developmental expression of a stage-specific transcription factor ac-Pou2

Differentiation and Maturation of Muscle and Fat Cells in Cultivated Seafood: Lessons from Developmental Biology

Cultivated meat, also known as cultured or cell-based meat, is meat produced directly from cultured animal cells rather than from a whole animal. Cultivated meat and seafood have been proposed as a means of mitigating the substantial harms associated with current production methods, including damage to the environment, antibiotic resistance, food security challenges, poor animal welfare, and-in the case of seafood-overfishing and ecological damage associated with fishing and aquaculture. Because biomedical tissue engineering research, from which cultivated meat draws a great deal of inspiration, has thus far been conducted almost exclusively in mammals, cultivated seafood suffers from a lack of established protocols for producing complex tissues in vitro. At the same time, fish such as the zebrafish Danio rerio have been widely used as model organisms in developmental biology. Therefore, many of the mechanisms and signaling pathways involved in the formation of muscle, fat, and other relevant tissue are relatively well understood for this species. The same processes are understood to a lesser degree in aquatic invertebrates. This review discusses the differentiation and maturation of meat-relevant cell types in aquatic species and makes recommendations for future research aimed at recapitulating these processes to produce cultivated fish and shellfish.

The Development and Evaluation of Brain and Heart Cell Lines from a Marine Fish for Use in Xenobiotic-Induced Cytotoxicity Testing

Two cell lines derived from the brain and heart of a Pacific white snook specimen (Centropomus viridis) were developed and evaluated in terms of their responsiveness to glyphosate-induced cytotoxicity. The cells were grown in Leibovitz-15 (L-15) medium supplemented with 10% fetal bovine serum (FBS) and were passaged 36 times. Growth was tested at different concentrations of FBS (5, 10 and 20%) at 27°C. The cell lines were cryopreserved at different passages and were successfully thawed, with a survival rate greater than 80% without detectable contamination. At passage 36, the cells were used to assess the deleterious effects of glyphosate, and cell proliferation was measured by direct counting and with the MTT assay. Similar LC₅₀ values were obtained with both methods. Although the principles behind these two assessment methods differ, our results show that both are suitable for evaluating glyphosate toxicity. In addition, heart- and brain-derived cells showed similar sensitivity, suggesting that the same mode of action might be responsible for the toxicity of glyphosate at the cellular level. The newly developed Pacific white snook brain and heart cell lines could be useful to investigate cellular and molecular mechanisms of toxicity, satisfying the need to reduce the use of animals in experiments. Glyphosate-related toxicological data obtained in the present study will allow us to continue investigating the effects of this herbicide directly on brain and heart fish cells since similar studies have only been carried out on either live organisms or on human cell lines such as neuroblastoma, which are immortalised by oncogenes or similar.

Cell Sources for Cultivated Meat: Applications and Considerations throughout the Production Workflow

Cellular agriculture is an emerging scientific discipline that leverages the existing principles behind stem cell biology, tissue engineering, and animal sciences to create agricultural products from cells in vitro. Cultivated meat, also known as clean meat or cultured meat, is a prominent subfield of cellular agriculture that possesses promising potential to alleviate the negative externalities associated with conventional meat production by producing meat in vitro instead of from slaughter. A core consideration when producing cultivated meat is cell sourcing. Specifically, developing livestock cell sources that possess the necessary proliferative capacity and differentiation potential for cultivated meat production is a key technical component that must be optimized to enable scale-up for commercial production of cultivated meat. There are several possible approaches to develop cell sources for cultivated meat production, each possessing certain advantages and disadvantages. This review will discuss the current cell sources used for cultivated meat production and remaining challenges that need to be overcome to achieve scale-up of cultivated meat for commercial production. We will also discuss cell-focused considerations in other components of the cultivated meat production workflow, namely, culture medium composition, bioreactor expansion, and biomaterial tissue scaffolding.

Development of a continuous cell line from larval Atlantic cod (Gadus morhua) and its use in the study of the microsporidian, Loma morhua

In vitro cell culture methods are crucial for the isolation, purification and mass propagation of intracellular pathogens of aquatic organisms. Cell culture infection models can yield insights into infection mechanisms, aid in developing methods for disease mitigation and prevention, and inform commercial-scale cultivation approaches. This study details the establishment of a larval cell line (GML-5) from the Atlantic cod (Gadus morhua) and its use in the study of microsporidia. GML-5 has survived over 100 passages in 8 years of culture. The line remains active and viable between 8 and 21°C in Leibovitz-15 (L-15) media with 10% foetal bovine serum and exhibits a myofibroblast phenotype as indicated by immuno-positive results for vimentin, α-smooth muscle actin, collagen I and S-100 proteins, while being desmin-negative. GML-5 supports the infection and development of two microsporidian parasites, an opportunistic generalist (Anncaliia algerae) and cod-specific Loma morhua. Using GML-5, spore germination and proliferation of L. morhua was found to require exposure to basic pH and cool incubation temperatures (8°C), in contrast to A. algerae, which required no cultural modifications. Loma morhua-associated xenoma-like structures were observed 2 weeks postexposure. This in vitro infection model may serve as a valuable tool for cod parasitology and aquaculture research.

Development and Characterization of a New Cell Line from Olive Flounder Paralichthys olivaceus

A new embryonic cell line (OFEC-17FEN) derived from olive flounder Paralichthys olivaceus was developed. OFEC-17FEN cells were subcultured for <30 passages over ~200 days. OFEC-17FEN cells had a doubling time of 114.34 h and modal diploid chromosome number was 48. The pluripotency genes POU5f1 and NANOG were expressed in OFEC-17FEN cells. However, the lack of several pluripotency-related genes expression indicates that OFEC-17FEN cells are not stem cells. OFEC-17FEN cells transfected with plasmid pEGFP-c1 exhibited a strong green fluorescent signal at 48 h after transfection. Accordingly, OFEC-17FEN cells may be useful for both basic research and biotechnological application.

Establishment and growth responses of Nile tilapia embryonic stem-like cell lines under feeder-free condition

Embryonic stem (ES) cells provide an invaluable tool for molecular analysis of vertebrate development and a bridge linking genomic manipulations in vitro and functional analysis of target genes in vivo. Work towards fish ES cells so far has focused on zebrafish (Danio renio) and medaka (Oryzias latipes). Here we describe the derivation, pluripotency, differentiation and growth responses of ES cell lines from Nile tilapia (Oreochromis niloticus), a world-wide commercial farmed fish. These cell lines, designated as TES1-3, were initiated from blastomeres of Nile tilapia middle blastula embryos (MBE). One representative line, TES1, showed stable growth and phenotypic characteristics of ES cells over 200 days of culture with more than 59 passages under feeder-free conditions. They exhibited high alkaline phosphatase activity and expression of pluripotency genes including pou5f3 (the pou5f1/oct4 homologue), sox2, myc and klf4. In suspension culture together with retinoic acid treatment, TES1 cells formed embryoid bodies, which exhibited expression profile of differentiation genes characteristics of all three germ cell layers. Notably, PKH26-labeled TES1 cells introduced into Nile tilapia MBE could contribute to body compartment development and led to hatched chimera formation with an efficacy of 13%. These results suggest that TES1 cells have pluripotency and differentiation potential in vitro and in vivo. In the conditioned DMEM, all of the supplements including the fetal bovine serum, fish embryonic extract, fish serum, basic fibroblast growth factor and non-protein supplement combination 5N were mitogenic for TES1 cell growth. This study will promote ES-based biotechnology in commercial fish.

Evolutionary Conservation of pou5f3 Genomic Organization and Its Dynamic Distribution during Embryogenesis and in Adult Gonads in Japanese Flounder Paralichthys olivaceus

Octamer-binding transcription factor 4 (Oct4) is a member of POU (Pit-Oct-Unc) transcription factor family Class V that plays a crucial role in maintaining the pluripotency and self-renewal of stem cells. Though it has been deeply investigated in mammals, its lower vertebrate homologue, especially in the marine fish, is poorly studied. In this study, we isolated the full-length sequence of Paralichthys olivaceus pou5f3 (Popou5f3), and we found that it is homologous to mammalian Oct4. We identified two transcript variants with different lengths of 3′-untranslated regions (UTRs) generated by alternative polyadenylation (APA). Quantitative real-time RT-PCR (qRT-PCR), in situ hybridization (ISH) and immunohistochemistry (IHC) were implemented to characterize the spatial and temporal expression pattern of Popou5f3 during early development and in adult tissues. Our results show that Popou5f3 is maternally inherited, abundantly expressed at the blastula and early gastrula stages, then greatly diminishes at the end of gastrulation. It is hardly detectable from the heart-beating stage onward. We found that Popou5f3 expression is restricted to the adult gonads, and continuously expresses during oogenesis while its dynamics are downregulated during spermatogenesis. Additionally, numerous cis-regulatory elements (CRE) on both sides of the flanking regions show potential roles in regulating the expression of Popou5f3. Taken together, these findings could further our understanding of the functions and evolution of pou5f3 in lower vertebrates, and also provides fundamental information for stem cell tracing and genetic manipulation in Paralichthys olivaceus.

Derivation and long-term culture of an embryonic stem cell-like line from zebrafish blastomeres under feeder-free condition

Existing zebrafish embryonic stem (ES) cell lines are derived and maintained using feeder layers. We describe here the derivation and long-term culture of an ES cell-like line derived from zebrafish blastomeres without the use of feeder cells. This line, designated as ZES1, has been maintained for more than 800 days in defined Dulbecco's modified Eagle's medium supplemented with fetal bovine serum, zebrafish embryo extract, trout serum, and human basic fibroblast growth factor. ZES1 cells possessed a morphology typical of ES cells, being round or polygonal in shape with a large nucleus and sparse cytoplasm and were mostly diploid. The cells formed individual colonies consisting of tightly packed cells that stained positively for alkaline phosphatase. ZES1 cells also formed embryoid bodies when transferred onto uncoated wells. The pluripotent nature of ZES1 cells was confirmed when they could be induced to differentiate in vitro into several cell types, through low- or high-density culture conditions. Treatment with retinoic acid also induced the differentiation of ZES1 cells into primarily neuronal cells. Using immunostaining and real-time polymerase chain reaction, we showed that Sox2, a known pluripotent marker in mammalian ES cells, was also present in ZES1 cells. Chimera experiments revealed that fluorescent-labeled ZES1 cells microinjected into zebrafish blastulas participated in the formation of all three germ layers. Using GFP-labeled ZES1 cells, chimera germline transmission was also demonstrated at the F1 generation. In conclusion, ZES1 cells possess both in vitro and in vivo pluripotency characteristics, indicating that nonmammalian ES cells can be readily derived and maintained for a long term under feeder-free culture conditions.

On the origin of POU5F1

BACKGROUND

Pluripotency is a fundamental property of early mammalian development but it is currently unclear to what extent its cellular mechanisms are conserved in vertebrates or metazoans. POU5F1 and POU2 are the two principle members constituting the class V POU domain family of transcription factors, thought to have a conserved role in the regulation of pluripotency in vertebrates as well as germ cell maintenance and neural patterning. They have undergone a complex pattern of evolution which is poorly understood and controversial.

RESULTS

By analyzing the sequences of POU5F1, POU2 and their flanking genes, we provide strong indirect evidence that POU5F1 originated at least as early as a common ancestor of gnathostomes but became extinct in a common ancestor of teleost fishes, while both POU5F1 and POU2 survived in the sarcopterygian lineage leading to tetrapods. Less divergent forms of POU5F1 and POU2 appear to have persisted among cartilaginous fishes.

CONCLUSIONS

Our study resolves the controversial evolutionary relationship between teleost pou2 and tetrapod POU2 and POU5F1, and shows that class V POU transcription factors have existed at least since the common ancestor of gnathostome vertebrates. It provides a framework for elucidating the basis for the lineage-specific extinctions of POU2 and POU5F1.

Establishing a cell line from Atlantic cod as a novel tool for in vitro studies

The present work describes the generation of a cell line from newly hatched Atlantic cod (Gadus morhua) larvae (ACL cells). Primary cultures were initiated by explant outgrowth from partially minced tissues and subcultured cells were exposed to UV radiation. After a substantial period of growth lag, cells started to proliferate and different growth conditions were tested to establish the cell line. At present, the ACL cell line has been subcultured for more than 100 passages. ACL cells had a polygonal shape and the morphology appeared homogenous with epithelial-like cells. Cell growth was dependent on the presence of foetal bovine serum and cells proliferated in a wide temperature range with optimal growth at 15 °C. By exposure to a viral dsRNA mimic (poly I:C) the cells expressed high levels of a repertoire of genes comprising both inflammatory mediators and interferon stimulated genes. Infection studies with two different viruses showed that infectious pancreatic necrosis virus (IPNV) propagated efficiently, and induced low level expression of genes of both pathways before the cells rapidly died. No productive infection was obtained with nervous necrosis virus (NNV), but a transient increase in the viral RNA level, followed by a high increase in expression of selected ISGs, suggests that the virus enters the cells but is unable to complete its replication cycle. To our knowledge, ACL cells are at the moment the only existing cell line from Atlantic cod. Our results demonstrate that ACL cells can be a useful research tool for further exploration of host-pathogen interactions and it is believed that this cell line will serve as a valuable tool also for studies within other research areas.

Identification of a pou2 ortholog in Chinese sturgeon, Acipenser sinensis and its expression patterns in tissues, immature individuals and during embryogenesis

The class V POU family genes, including pou5f1 and pou2, encode transcription factors critical for the maintenance of pluripotency in embryonic stem cells (ESC) and germ line cells in vertebrates. In the present study, the full-length cDNA of a pou2 ortholog in A. sinensis, Aspou2, was cloned and sequenced. This cDNA sequence is 2,853 base pairs in length and encodes a peptide of 431 amino acid residues. A comparison of the deduced amino acid sequence of Aspou2 with that of other vertebrate species showed that they were highly conserved in the POU domain, which shared 88 and 90% identity with that of zebrafish and medaka, respectively, and was 69, 67 and 67% identical to frog, mouse and human, respectively. RT-PCR analysis revealed that Aspou2 was detected in all tissues examined except for the liver, and high mRNA levels of Aspou2 were found in the muscle, pituitary and brain. During the embryogenesis and early larval development, the expression level of Aspou2 mRNAs decreased gradually apart from 1-day larvae that were not observed. Furthermore, Aspou2 seemed to raise with the development of gonads of immature Chinese sturgeons. These results suggested the possible involvement of Aspou2 in the nonpluripotent cells, pluripotent cells, embryogenesis, and gonad development.

Low impact of exposure to environmentally relevant doses of 226Ra in Atlantic cod (Gadus morhua) embryonic cells

The aim of this study was to investigate whether (226)Ra, a radionuclide present in produced water from oil platforms in the North Sea and other offshore drilling areas, could affect vulnerable early life stages of Atlantic cod (Gadus morhua). Blastula-stage embryonic cells (EC) from fertilized eggs of Atlantic cod were isolated and exposed to environmental relevant concentrations of (226)Ra and transcription of selected genes quantified. The results showed a weak, but significant up-regulation of GPx3 and HSP70 transcripts after 48 h of exposure to 2.11 Bq/L. In EC exposed to three (226)Ra concentrations (2.11, 23 and 117 Bq/L) for 12 h, metallothionein, HSP90AA, thioredoxin and caspase 8 were significantly up-regulated in cells exposed to 117 Bq/L, whereas thioredoxin was also significantly up-regulated in EC exposed to 23 Bq/L. When EC were exposed to the same (226)Ra concentrations for 48 h, only heme oxygenase was significantly up-regulated in the 23 Bq/L exposure group. The results suggest that environmentally relevant activities of (226)Ra may induce oxidative stress and apoptosis in fish ECs. Exposure of Atlantic cod EC to Cd, selected as a model toxicant, supported the ability of EC around blastula stage to respond to toxicants by altered transcription. Due to dilution, environmentally relevant concentrations of radionuclides present in produced water would be expected to pose a minor threat to early life stages of fish.

Fish stem cell cultures

Stem cells have the potential for self-renewal and differentiation. First stem cell cultures were derived 30 years ago from early developing mouse embryos. These are pluripotent embryonic stem (ES) cells. Efforts towards ES cell derivation have been attempted in other mammalian and non-mammalian species. Work with stem cell culture in fish started 20 years ago. Laboratory fish species, in particular zebrafish and medaka, have been the focus of research towards stem cell cultures. Medaka is the second organism that generated ES cells and the first that gave rise to a spermatogonial stem cell line capable of test-tube sperm production. Most recently, the first haploid stem cells capable of producing whole animals have also been generated from medaka. ES-like cells have been reported also in zebrafish and several marine species. Attempts for germline transmission of ES cell cultures and gene targeting have been reported in zebrafish. Recent years have witnessed the progress in markers and procedures for ES cell characterization. These include the identification of fish homologs/paralogs of mammalian pluripotency genes and parameters for optimal chimera formation. In addition, fish germ cell cultures and transplantation have attracted considerable interest for germline transmission and surrogate production. Haploid ES cell nuclear transfer has proven in medaka the feasibility of semi-cloning as a novel assisted reproductive technology. In this special issue on "Fish Stem Cells and Nuclear Transfer", we will focus our review on medaka to illustrate the current status and perspective of fish stem cells in research and application. We will also mention semi-cloning as a new development to conventional nuclear transfer.