During zebrafish development, a gradient of stromal-derived factor 1a (Sdf1a) provides the directional cue that guides the migration of the primordial germ cells (PGCs) to the gonadal tissue. Here we describe a method to produce large numbers of infertile fish by inducing ubiquitous expression of Sdf1a in zebrafish embryos resulting in disruption of the normal PGC migration pattern. A transgenic line of zebrafish, Tg(hsp70:sdf1a-nanos3, EGFP), was generated that expresses Sdf1a under the control of the heat-shock protein 70 (hsp70) promoter and nanos3 3?UTR. To better visualize the PGCs, the Tg(hsp70:sdf1a-nanos3, EGFP) fish were crossed with another transgenic line, Tg(kop:DsRed-nanos3), that expresses DsRed driven by the PGC-specific kop promoter. Heat treatment of the transgenic embryos caused an induction of Sdf1a expression throughout the embryo resulting in the disruption of their normal migration. Optimal embryo survival and disruption of PGC migration was achieved when transgenic embryos at the 4- to 8-cell stage were incubated at 34.5°C for 18 hours. Under these conditions, disruption of PGC migration was observed in 100% of the embryos. Sixty-four adult fish were developed from three separate batches of heat-treated embryos and all were found to be infertile males. When each male was paired with a wild-type female, only unfertilized eggs were produced and histological examination revealed that each of the adult male fish possessed severely under-developed gonads that lacked gametes. The results demonstrate that inducible Sdf1a expression is an efficient and reliable strategy to produce infertile fish. This approach makes it convenient to generate large numbers of infertile adult fish while also providing the capability to maintain a fertile brood stock.

/pdf/inducible-sterilization-of-zebrafish-by-disruption-of-dw3bf9cw6u.pdf

Inducible Sterilization of Zebrafish by Disruption of Primordial Germ Cell Migration

Methods of disrupting germ cell migration and development in a fish embryo by inducing targeted expression of Sdf-1 a or Lif and disruption of the Sdf-1 a gradient or a Lif signaling pathway in the fish embryo have been developed. Plasmid constructs containing a gene encoding Sdf-1 a or Lif and a gene encoding a signaling sequence for targeted expression of Sdf-1 a or Lif have been generated. The plasmids will be administered to a fish or a population of fish to reproductively sterilize the population with efficacy of up to 100%. Transgenic fish of this invention are reproductively incompetent of genetically contaminating a wild fish population.

Efficient sterilization of fish by disruption of germ cell development

Methods for the production of reproductively sterile fish and aquatic animals for aquaculture, the aquarium trade, and control of invasive species are described. The methods include disruption of gonadal development through the administration of compounds that lead to the failure of fertile gonadal development. Compounds may be delivered to the eggs prior to fertilization or water activation or post fertilization and water activation by contacting unfertilized or pre-water-activated fertilized eggs or fertilized eggs in an immersion medium including the compound of interest. Compounds may be conjugated with a molecular transporter compound effective for chorionic transport of the conjugate. The compounds may be antisense Morpholino oligomers that are capable of effectively suppressing the expression of the dead end gene or other essential genes for germ cell development in fish and other egg-producing aquatic animals.

Method of producing infertile fish and egg-producing aquatic animals and of delivering compounds into eggs and embryos

Provided herein are methods of sterilizing fish by contacting an embryonic or juvenile fish with a compound of formula (I). In some embodiments, the compound is primordazine or a derivative thereof.

Germ cell ablation compounds and uses thereof

Reproductive containment in farmed fish is highly desired for sustainable aquaculture to prevent genetic introgression with wild conspecifics and enhance productivity by suppressing sexual maturation. A number of strategies have already been implemented or have been tested in commercially important fish (e.g. triploidy, monosexing, hormonal therapies); however, they either do not result in 100% containment, or they cannot be applied to all species. One promising new approach consists in disrupting primordial germ cells (PGCs), at the origin of germline cells, to induce sterility. The work carried out in this doctoral thesis aimed to investigate the genes involved in the survival of germ cells and subsequently conduct a functional analysis of candidate genes using CRISPR/Cas9 gene editing system to ultimately provide the basis for the development of a novel sterilisation technique. Nile tilapia was chosen as the experimental animal as it is a major aquaculture species worldwide and the control of reproduction plays a critical role in the farming productivity in this species. In addition, the species has clear advantages as its whole genome sequence is accessible, the generation time is relatively short and zygotes can be available all year round. Initially, a panel of 11 candidate genes with reported roles in survival of PGCs was investigated during the ontogenic development which led to the selection of piwi-like (piwil) gene as a target for genome editing. Then, high temperature was tested as a means to induce germ cell loss to better understand the mechanism underlying germ cell survival and apoptosis, and this study confirmed the functional importance of piwil genes in relation to germ cell loss and proliferation. In addition, the study suggested potential subfunctionalisation within the Bcl-2 gene family which requires further investigation. The next step aimed to optimise the CRISPR/Cas9 gene editing method by improving the microinjection system and testing different concentrations of sgRNAs. Over 95% of injected embryos showed on-target mutation in piwil2 via zygote injection of CRISPR/Cas9 reagents and complete KO larvae were shown in half of the mutants, producing putative sterile fish. However, there was no clear association between the phenotypes in PGCs and the mutation rate. Further comparative studies of mutant screening methods including T7E1, RGEN, HRMA, fragment analysis and NGS revealed that the genotypes of F0 are highly mosaic, suggesting that deep sequencing is recommended for accurate and high throughput F0 screening and further improvement for predictable genome editing is required for a reliable gene functional analysis in F0. In summary, the current thesis provided new scientific knowledge and supporting evidence for the use of the CRISPR/Cas9 gene editing platform to study gene function associated with sterility, with the ultimate goal to develop an alternative sterilisation method in fish.

Research towards the effective disruption of reproductive competence in Nile tilapia Oreochromis niloticus

The present invention provides for a method for inducing sterility in fish by administering at least one compound that disrupts the establishment of the gonadotropin-releasing hormone system during early development thereby inhibiting sexual maturity in the treated fish. Effective compounds include GABA, GABA receptor agonists, or GABA receptor antagonists.

Inducing sterility in fish by disrupting the development of the GnRH system

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Inducing sterility in fish by disrupting the development of the GnRH system