A recent breakthrough in the proliferation of germline stem cells (GSCs) could have big implications for commercial aquaculture.
A team of Japanese researchers has achieved the first in-vitro mass proliferation of rainbow trout GSCs by via transplant into recipient fish - a method used for quickly increasing numbers of endangered species.
Cryopreservation of germline stem cells (GSCs) harvested from endangered fish species, and their subsequent transplant into recipient fish, allows the recipient fish to develop the gonads of the donor species – which in turn causes the fish to reproduce the donor species.
However, the number of GSCs that can be harvested from donor individuals is typically not sufficient for this process to work, especially for fish species with small gonads. The new method allows the expansion of the number of GSCs in vitro, so that a theoretically unlimited amount of GSC could be produced from a single sample.
The number of GSCs is greater in testes than in ovaries, so the researchers only used testicular GSCs, having already learned that when transplanted into a female host, GSCs from male donors will develop into ovaries.
In a paper published 15 June in Communications Biology, the team, mainly from Tokyo University of Marine Science and Technology, explains that to reconstruct the microenvironment that surrounds GSCs inside the gonads, they created a feeder layer derived from Sertoli cells and used a culture medium containing trout blood plasma.
The GSCs were cultured in petri dishes for 28 days and then transplanted to male and female rainbow trout. These recipients developed the gonads of the donor and went on, in two years, to breed and successfully produce offspring of the donor.
It is currently not possible to successfully freeze fish eggs or embryos as a method of preserving endangered species. However, GSCs can be frozen and later successfully transplanted, so the ability to multiply the amount of GSCs available is a huge breakthrough.
It also has applications in commercial aquaculture. The idea of transplanting GSCs from bluefin tuna into the related mackerel was proposed in 2015 by one of the current study’s authors, Goro Yoshizaki. Mackerel are not endangered, and they mature to the reproductive stage within one year instead of the five years needed for bluefin, and their care and feeding is much easier due their small size.
In a paper to be published September 2020 in General and Comparative Endocrinology (and already available online) to which Yoshizaki also contributed, the suitability of hybrid mackerel (Scomber australasicus × S. japonicus) with germ cell-less sterile gonads as a recipient for transplantation of bluefin tuna germ cells is examined.
Most of the crossbred mackerel were found to lack their own GSCs and were thus sterile, though they possessed the cells needed for nursing donor-derived germ cells needed to support donor GSCs. Since their own sterile gonads would not be competing with that of the donor, they would make promising candidates as recipient fish for bluefin tuna. A transplantation revealed that donor cells were successfully incorporated into the recipient’s gonads.
Photo courtesy of Elena Pavlovich/Shutterstock
