Scientists introduced alligator DNA into catfish to create hybrid

A team of scientists inserted an alligator gene into the genomes of catfish. The alligator gene called cathelicidin is an antimicrobial gene that plays a role in the animal's innate immune response, providing defense against various pathogens, including bacteria and viruses.

Researchers inserted the gene into the part of the catfish genome that codes for an essential reproductive hormone. The produced hybrids showed increased disease resistance and sterility.

Healthier and sterile hybrids

Aquaculture not just contributes to climate change but also suffers from its impacts. Catfish comprise more than 50 percent of the farm-raised fish demand in the US; however, almost 45 percent of the total population does not survive past the fingerling stage, threatening the environment and the industry's sustainability.

Catfish are not just highly susceptible to bacterial infections and abiotic stresses but have also developed antibiotic resistance. Scientists are trying to give these freshwater farm fish an edge against the circumstances by infusing them with a disease-fighting gene from alligators.

The CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) system has revolutionized gene modification, making gene editing more precise, efficient, and accessible. A team led by Rex Dunham and Baofeng Su at Auburn University, Alabama, used Cas9 – one of the enzymes produced by the CRISPR system – to integrate the cathelicidin gene from alligators into the catfish DNA.

The cathelicidin transgenic fish's survival rate is 100-400 percent more than their native counterparts. The sterility of these hybrids helps preclude their impact on ecosystems and "prevent the establishment of transgenic or domestic genotypes in the natural environment," says the team.

Viability and ethical concerns

While ensuring that these genetically modified fish do not alleviate concerns of breeding with and outcompeting their wild counterparts, it is difficult to discount the lack of use farmers have for sterile fish produced in a lab.

The use of CRISPR also casts doubt on the viability of the technique as it may prove "too difficult to produce enough of these fish to get a viable, genetically healthy line going," says Greg Lutz, an expert on aquaculture genetics at Louisiana State University.

There is also uncertainty surrounding the approval of these transgenic fish for human consumption due to the ethical concerns surrounding genetic modification and the potential for unintended consequences when using CRISPR. Lastly, although the researchers assert they would "eat it in a heartbeat," public acceptance of alligator hybrid fish is an inevitable challenge.

The research has yet to be peer-reviewed and is available as a preprint on bioRxiv.

Abstract:

The CRISPR/Cas9 platform holds promise for modifying fish traits of interest as a precise and versatile tool for genome manipulation. To reduce introgression of transgene and control reproduction, catfish species have been studied for upscaled disease resistance and intervening of reproduction to lower the potential environmental risks of introgression of escapees' as transgenic animals. Taking advantage of the CRISPR/Cas9-mediated system, we succeeded in integrating the cathelicidin gene from an alligator (Alligator sinensis; As-Cath) into the target luteinizing hormone (LH) locus of channel catfish (Ictalurus punctatus) using two delivery systems assisted by double-stranded DNA (dsDNA) and single-stranded oligodeoxynucleotides (ssODNs), respectively. In this study, high knock-in (KI) efficiency (22.38%, 64/286) but low on-target was achieved using the ssODN strategy, whereas adopting a dsDNA as the donor template led to an efficient on-target KI (10.80%, 23/213). On-target KI of As-Cath was instrumental in establishing the LH knockout (LH−_As-Cath+) catfish line, which displayed heightened disease resistance and reduced fecundity compared to the wild-type sibling fish. Furthermore, implanting with HCG and LHRHa can restore the fecundity, spawnability and hatchability of the new transgenic fish line. Overall, we replaced the LH gene with an alligator cathelicidin transgene and then administered hormone therapy to gain complete reproductive control of disease-resistant transgenic catfish in an environmentally sound manner. This strategy not only effectively improves the consumer-valued traits, but also guards against genetic contamination. This is a breakthrough in aquaculture genetics to confine fish reproduction and prevent the establishment of transgenic or domestic genotypes in the natural environment.