Enhancing the efficiency of hybrid catfish (♀ channel catfish, Ictalurus punctatus, × ♂ blue catfish, I. furcatus) embryo production through xenogenesis

Abstract

Xenogenesis has been identified as an innovative technology for hybrid catfish (♀ channel catfish, Ictalurus punctatus × ♂ blue catfish, I.furcatus) embryo production. The xenogeneic process can be accomplished by transplanting primordial germ cells (PGCs), spermatogonial stem cells (SSCs), or oogonial stem cells (OSCs), derived from a donor diploid fish into a sterile recipient, which then enables the recipient fish to produce donor-derived gametes. However, still there are some challenges in xenogenesis that need to be optimized in commercial-scale hybrid catfish embryo production. Hence, a series of experiments were conducted to enhance the efficiency of hybrid catfish embryo production through xenogenesis. Until recently, the timing of transplantation of donor cells into hosts was done with limited knowledge of the best age to inject cells. The age of the host could critically affect the success of germ cell transplantation. Hence, one of the study conducted to identify the best age of the triploid channel catfish to transplant blue catfish stem cells for production of xenogeneic catfish and it was identified that 4 to 6 DPH is a suitable timespan to inject donor-derived stem cells into recipients. However, having a host with a short maturation time and smaller body size than channel catfish would be ideal for commercial application. To address that issue, another study was conducted to assess the effectiveness of triploid white catfish (Ameiurus catus) as a host species to transplant blue and channel catfish stem cells during the production process of xenogeneic catfish. It was demonstrated the suitability of white catfish as a host species by transplanting stem cells between 4 - 5 DPH for commercial-scale hybrid catfish production. In all the above experiments, freshly extracted stem cells are used to create xenogens, which is challenging, especially considering germ cell production is donor size and age specific as well as dependent on seasonal cycles. Thus, having frozen stem cells available in germplasm repositories will help to facilitate xenogenesis technology for hybrid catfish production. Hence another study was conducted to assess the effectiveness of fresh and cryopreserved stem cells for germ cell transplantation to support xenogenesis and it was revealed that cryopreserved donor stem cells can recover in recipient gonads and perform as well as their freshly extracted counterparts. Further, the collection of an adequate number of stem cells for transplantation and cells damaged by proteinases (trypsinization) during the procedure of stem cell extraction were major challenges that required to be addressed. Hence, in vitro propagation of stem cells has emerged as a potential solution. Thus, the final study aimed to identify the best culture medium for in vitro propagation of blue catfish stem cells for further identification of optimum culture parameters and it was identified that Dulbecco's Modified Eagle's Medium (DMEM) supplemented with 10% fetal bovine serum (FBS) is the most suitable culture medium combination for in vitro propagation of SSCs. Overall, these findings will enhance the efficiency of germ cell transplantation for commercial-scale hybrid catfish production.

Keywords: xenogenesis, triploids, stem cell transplantation, cryopreservation, cell colonization, proliferation