Diploidized eggs reprogram adult somatic cell nuclei to pluripotency in nuclear transfer in medaka fish (Oryzias latipes)

Embryonic fate after somatic cell nuclear transfer in non-enucleated goldfish oocytes is determined by first cleavages and DNA methylation patterns

Reducing the variability in nuclear transfer outcome requires a better understanding of its cellular and epigenetic determinants, in order to ensure safer fish regeneration from cryobanked somatic material. In this work, clones from goldfish were obtained using cryopreserved fin cells as donor and non-enucleated oocytes as recipients. We showed that the high variability of clones survival was not correlated to spawn quality. Clones were then characterized for their first cleavages pattern in relation to their developmental fate up to hatching. The first cell cycle duration was increased in clones with abnormal first cleavage, and symmetric first two cleavages increased clone probability to reach later on 24 h- and hatching-stages. At 24 h-stage, 24% of the clones were diploids and from donor genetic origin only. However, ploidy and genetic origin did not determine clones morphological quality. DNA methylation reprogramming in the promoter region of pou2, nanog, and notail marker genes was highly variable, but clones with the nicest morphologies displayed the best DNA methylation reprogramming. To conclude, non-enucleated oocytes did allow authentic clones production. The first two cell cycles were a critical determinant of the clone ability to reach hatching-stage, and DNA methylation reprogramming significantly influenced clones morphological quality.

Somatic cell nuclear transfer in non-enucleated goldfish oocytes: understanding DNA fate during oocyte activation and first cellular division

Nuclear transfer consists in injecting a somatic nucleus carrying valuable genetic information into a recipient oocyte to sire a diploid offspring which bears the genome of interest. It requires that the oocyte (maternal) DNA is removed. In fish, because enucleation is difficult to achieve, non-enucleated oocytes are often used and disappearance of the maternal DNA was reported in some clones. The present work explores which cellular events explain spontaneous erasure of maternal DNA, as mastering this phenomenon would circumvent the painstaking procedure of fish oocyte enucleation. The fate of the somatic and maternal DNA during oocyte activation and first cell cycle was studied using DNA labeling and immunofluorescence in goldfish clones. Maternal DNA was always found as an intact metaphase within the oocyte, and polar body extrusion was minimally affected after oocyte activation. During the first cell cycle, only 40% of the clones displayed symmetric cleavage, and these symmetric clones contributed to 80% of those surviving at hatching. Maternal DNA was often fragmented and located under the cleavage furrow. The somatic DNA was organized either into a normal mitotic spindle or abnormal multinuclear spindle. Scenarios matching the DNA behavior and the embryo fate are proposed.

Application of interspecific Somatic Cell Nuclear Transfer (iSCNT) in sturgeons and an unexpectedly produced gynogenetic sterlet with homozygous quadruple haploid

Somatic cell nuclear transfer (SCNT) is a very promising cloning technique for reconstruction of endangered animals. The aim of the present research is to implement the interspecific SCNT (iSCNT) technique to sturgeon; one fish family bearing some of the most critically endangered species. We transplanted single cells enzymatically isolated from a dissociated fin-fragment of the Russian sturgeon (Acipenser gueldenstaedtii) into non-enucleated eggs of the sterlet (Acipenser ruthenus), two species bearing different ploidy (4n and 2n, respectively). Up to 6.7% of the transplanted eggs underwent early development, and one feeding larva (0.5%) was successfully produced. Interestingly, although this transplant displayed tetraploidism (4n) as the donor species, the microsatellite and species-specific analysis showed recipient-exclusive homozygosis without any donor markers. Namely, with regards to this viable larva, host genome duplication occurred twice to form tetraploidism during its early development, probably due to iSCNT manipulation. The importance of this first attempt is to apply iSCNT in sturgeon species, establishing the crucial first steps by adjusting the cloning-methodology in sturgeon's biology. Future improvements in sturgeon's cloning are necessary for providing with great hope in sturgeon's reproduction.

Autotetraploid cell line induced by SP600125 from crucian carp and its developmental potentiality

Polyploidy has many advantages over diploidy, such as rapid growth, sterility, and disease resistance, and has been extensively applied in agriculture and aquaculture. Though generation of new polyploids via polyploidization has been achieved in plants by different ways, it is comparatively rare in animals. In this article, by a chemical compound, SP600125, polyploidization is induced in fish cells in vitro, and a stable autotetraploid cell line has been generated from diploid fibroblast cells of crucian carp. As a c-Jun N-terminal kinase (Jnk) inhibitor, SP600125 does not function during the induction process of polyploidization. Instead, the p53 signal pathway might be involved. Using the SP600125-induced tetraploid cells and eggs of crucian carp as the donors and recipients, respectively, nuclear transplantation was conducted such that tetraploid embryos were obtained. It suggests that combining polyploidization and the somatic cell nuclear transfer technique (SCNT) is an efficient way to generate polyploidy, and the presented method in this research for generating the tetraploid fish from diploid fish can provide a useful platform for polyploid breeding.

A protocol for adult somatic cell nuclear transfer in medaka fish (Oryzias latipes) with a high rate of viable clone formation

Previously, we successfully generated fully grown, cloned medaka (the Japanese rice fish, Oryzias latipes) using donor nuclei from primary culture cells of adult caudal fin tissue and nonenucleated recipient eggs that were heat shock-treated to induce diploidization of the nuclei. However, the mechanism of clone formation using this method is unknown, and the rate of adult clone formation is not high enough for studies in basic and applied sciences. To gain insight into the mechanism and increase the success rate of this method of clone formation, we tested two distinct nuclear transfer protocols. In one protocol, the timing of transfer of donor nuclei was changed, and in the other, the size of the donor cells was changed; each protocol was based on our original methodology. Ultimately, we obtained an unexpectedly high rate of adult clone formation using the protocol that differed with respect to the timing of donor nuclei transfer. Specifically, 17% of the transplants that developed to the blastula stage ultimately developed into adult clones. The success rate with this method was 13 times higher than that obtained using the original method. Analyses focusing on the reasons for this high success rate of clone formation will help to elucidate the mechanism of clone formation that occurs with this method.

Nuclear transfer of embryonic cell nuclei to non-enucleated eggs in zebrafish, Danio rerio

We previously established a novel method for nuclear transfer in medaka (Oryzias latipes) using non-enucleated, diploidized eggs as recipients for adult somatic cell nuclei. Here we report the first attempt to apply this method to another fish species. To examine suitability of using non-enucleated eggs as recipients for nuclear transfer in the zebrafish (Danio rerio), we transferred blastula cell nuclei from a wild-type donor strain to non-enucleated, unfertilized eggs from a golden recipient strain. As a result, 31 of 184 (16.8%) operated eggs developed normally and reached the adult stage. Twenty-eight (15.2%) of these transplants showed wild-type phenotype and the remaining three (1.6%) were golden. Except for one individual that exhibited diploid/tetraploid mosaicism, all of the wild-type nuclear transplants were either triploid or diploid. While all of 19 triploid transplants were infertile, a total of six transplants (21.4%) were fertile (five of the eight diploid transplants and one transplant exhibiting ploidy mosaicism). Except for one diploid individual, all of the fertile transplants transferred both the wild-type golden gene allele (slc24a5) as well as the phenotype, the wild-type body color, to their F₁ and F₂ progeny in a typical Mendelian fashion. PCR analysis of slc24a5 suggested that triploidy originated from a fused nucleus in the diploid donor and haploid recipient nuclei, and that the sole origin of diploidy was the diploid donor nucleus. The results of the present study demonstrated the suitability of using non-enucleated eggs as recipients for nuclear transfer experiments in zebrafish.

Somatic cells derived from haploid larvae are feasible as donors for nuclear transplant in zebrafish. Preliminary results

Summary Somatic cells derived from zebrafish haploid larval (both androgenetic and gynogenetic) cultures were used as donors for nuclear transplant into non-enucleated oocytes. Nuclei were transplanted either before or simultaneously with oocyte activation in the central region and in the incipient animal pole, respectively. Against expected results, 20% of transplanted embryos during oocyte activation using cells of gynogenetic origin reached the 100% epiboly stage, even two survived for up to 5 days, whereas no development was observed when cells from androgenetic origin were used. Results derived from this work open a novel possibility of studying somatic cell reprogramming and imprinting phenomena in zebrafish.

Optimization of somatic cell injection in the perspective of nuclear transfer in goldfish

Background

Nuclear transfer has the potential to become one strategy for fish genetic resources management, by allowing fish reconstruction from cryopreserved somatic cells. Survival rates after nuclear transfer are still low however. The part played by unsuitable handling conditions is often questioned, but the different steps in the procedure are difficult to address separately. In this work led on goldfish (Carassius auratus), the step of somatic cells injection was explored. Non-enucleated metaphase II oocytes were used as a template to explore the toxicity of the injection medium, to estimate the best location where the cell should be injected, and to assess the delay necessary between cell injection and oocyte activation.

Results

Trout coelomic fluid was the most suitable medium to maintain freshly spawned oocytes at the metaphase II stage during oocyte manipulation. Oocytes were then injected with several media to test their toxicity on embryo development after fertilization. Trout coelomic fluid was the least toxic medium after injection, and the smallest injected volume (10 pL) allowed the same hatching rates as the non injected controls (84.8% ± 23). In somatic cell transfer experiments using non enucleated metaphase II oocytes as recipient, cell plasma membrane was ruptured within one minute after injection. Cell injection at the top of the animal pole in the oocyte allowed higher development rates than cell injection deeper within the oocyte (respectively 59% and 23% at mid-blastula stage). Embryo development rates were also higher when oocyte activation was delayed for 30 min after cell injection than when activation was induced without delay (respectively 72% and 48% at mid-blastula stage).

Conclusions

The best ability of goldfish oocytes to sustain embryo development was obtained when the carrier medium was trout coelomic fluid, when the cell was injected close to the animal pole, and when oocyte activation was induced 30 min after somatic cell injection. Although the experiments were not designed to produce characterized clones, application of these parameters to somatic cell nuclear transfer experiments in enucleated metaphase II oocytes is expected to improve the quality of the reconstructed embryos.

Exploring novel hormones essential for seawater adaptation in teleost fish

Marine fish are dehydrated in hyperosmotic seawater (SW), but maintain water balance by drinking surrounding SW if they are capable of excreting the excess ions, particularly Na(+) and Cl(-), absorbed with water by the intestine. An integrative approach is essential for understanding the mechanisms for SW adaptation, in which hormones play pivotal roles. Comparative genomic analyses have shown that hormones that have Na(+)-extruding and vasodepressor properties are greatly diversified in teleost fish. Physiological studies at molecular to organismal levels have revealed that these diversified hormones are much more potent and efficacious in teleost fish than in mammals and are important for survival in SW and for maintenance of low arterial pressure in a gravity-free aquatic environment. This is typified by the natriuretic peptide (NP) family, which is diversified into seven members (ANP, BNP, VNP and CNP1, 2, 3 and 4) and exerts potent hyponatremic and vasodepressor actions in marine fish. Another example is the guanylin family, which consists of three paralogs (guanylin, uroguanylin and renoguanylin), and stimulates Cl(-) secretion into the intestinal lumen and activates the absorptive-type Na-K-2Cl cotransporter by local luminocrine actions. The most recent addition is the adrenomedullin (AM) family, which has five members (AM1, 2, 3, 4 and 5), with AM2 and AM5 showing the most potent or efficacious vasodepressor and osmoregulatory effects among known hormones in teleost fish. Accumulating evidence strongly indicates that members of these diversified hormone families play essential roles in SW adaptation in teleost fish. In this short review, the author has attempted to propose a novel approach for identification of new hormones that are important for SW adaptation using comparative genomic and functional studies. The author has also suggested potential hormone families that are diversified in teleost fish and appear to be involved in SW adaptation through their ion-extruding actions.