GM fish made quickly
Transgenic transplant technique could aid endangered species.
A new technique that speeds up the production of genetically modified fish could help to preserve endangered species such as Atlantic salmon and Gila trout1.
So far the trick has been used to nurture genetically modified trout cells into live fry. "Other researchers will now double their efforts to get this to work in other species, like zebrafish," says fish biologist Brendan McAndrew of Stirling University, UK.
Small transgenic zebrafish are commonplace in the lab, where they help researchers to study the effects of genes on development. Larger species have been modified for commercial gain - salmon have been altered to grow larger and survive low temperatures.
But production techniques are time-consuming, expensive and unpredictable. Methods that work in mice fail to produce fertile fish. "We can't convert fish embryonic stem cells into eggs and sperm," explains Goro Yoshizaki from Tokyo University of Fisheries.
Instead, Yoshizaki's team extracted primordial germ cells (PGCs), which only give rise to sex cells, from the gonads of immature fish. The team implanted up to ten PGCs, modified to make a fluorescent green marker protein, into the body cavity of 74 freshly hatched rainbow trout (Oncorhynchus mykiss).
In 16 of the fish, the cells migrated to the gonads, where their green glow revealed them turning into eggs or sperm. After normal fertilization, 4% of these sex cells developed into live fry. The success rate is low, but could be improved by implanting PGCs into sterile fish, Yoshisaki speculates.
The technique is twice as fast as conventional methods - in which genetically modified fish are selected after an extra round of breeding. "It used to be a long process," says developmental biologist Yaniv Hinits of Kings College London. Trout take a year to mature and spawn only annually.
The method may help to safeguard endangered fish. Fish eggs and embryos are too large to survive cold storage, so there is no way to preserve them. PGCs are smaller. "It should be possible to freeze and revive them," says McAndrew. Stored PGCs could even be matured in surrogates of another species, Yoshizaki adds.
The cells may also help to feed the world's sushi habit. Tuna PGCs, for example, could be transplanted into sterile mackerel. The smaller fish are cheaper to house and could produce large numbers of tuna sperm and eggs quickly. Juveniles could be reared in a hatchery and released into the sea, says Yoshizaki.
- Takeuchi, Y., Yoshizaki, G. & Takeuchi, T. Generation of live fry from intraperitoneally transplanted primordial germ cells in rainbow trout. Biology of Reproduction, 69, 1142 - 1149, doi:10.1095/biolreprod.103.017624 (2003).
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