Biological Confinement of Genetically Engineered Organisms (2004) / Chapter Skim
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4. Bioconfinement of Animals: Fish, Shellfish, and Insects
4. Bioconfinement of Animals: Fish, Shellfish, and Insects
Pages 130-158
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From page 130... ...
Their reproductive and ecological traits are closely related to those of their wild relatives, thus raising the possibility of gene flow to or competition with wild relatives. Furthermore, many of the species of fish, shellfish, and insects targeted for genetic engineering have wild relatives in the environments they are likely to enter.
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From page 131... ...
Scientists also are developing transgenic lines for use as biofactories to produce pharmaceuticals, industrial chemicals, or dietary supplements; in bioremediation to remove contaminants from water; as water quality sentinels to detect contaminants that damage the genes of living organisms; and for biological control of nuisance aquatic species. Some degree of mechanical and physical confinement is possible for some of the proposed transgenic fish and shellfish (Scientists' Working Group on Biosafety, 1998)
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From page 132... ...
BIOCONFINEMENT OF FISH AND SHELLFISH Bioconfinement methods currently in practice for fish and shellfish either reduce the spread of transgenes and transgenic traits through disruption of sexual reproduction or rely on ecological characteristics of the production site that are lethal to some life stage of an escaping organism. Disruption of Sexual Reproduction Methods for disruption of sexual reproduction include induction of triploidy or interploid triploidy -- causing embryos that normally bear two
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From page 133... ...
Sterilization through Induction of Triploidy Triploidy induction involves application of hydrostatic pressure or temperature or chemical shock at the appropriate number of minutes after egg fertilization to disrupt the egg's normal extrusion of a polar body that contains a haploid set of chromosomes. The resulting retention of the polar body leads to an embryo that bears a pair of haploid chromosome sets from the female (instead of the normal single set)
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From page 134... ...
or tetraploidy (4n) occurs by temperature shock, chemical shock, or pressure at an appropriate time after fertilization: denotes the point at which the shock is applied; denotes one haploid chromosome set derived from the female parent; and + denotes one haploid chromosome set derived from the male.
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From page 135... ...
also can compromise sterility if their gonads are diploid and thus develop into normal, fertile gametes. Sterile individuals that still enter into courtship behavior could disrupt successful reproduction of wild relatives, and recurring large escapes of sterile individuals could heighten competition with or predation on wild species.
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From page 136... ...
. Screening to mitigate failed triploidization: Less than total triploid induction can be mitigated by screening treated individuals and then removing the nontriploids before they are transferred from hatcheries to much less secure grow-out facilities, such as outdoor ponds or open-water cages (Kapuscinski, 2001; Kapuscinski and Brister, 2001)
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From page 137... ...
, the main question would be whether the net fitness of trans genic salmon is higher or lower than in currently farmed strains and thus whether the transgenic fish would be more or less of a threat to invade native regions (NRC, 2002b; Pew Initiative on Food and Biotechnology, 2003)
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From page 138... ...
The proposal also would protect the company's patent on the marketed line of transgenic fish by preventing salmon farmers from propagating the line because they would be required to purchase production fish for each grow-out cycle. The Aqua Bounty Farms proposal has two important weaknesses.
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From page 139... ...
However, Aqua Bounty Farms has publicly sug gested that the cost advantage of producing faster-growing transgenic salmon could give salmon farming companies enough economic leeway to make the switch to land-based production (McClure, 2002)
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From page 140... ...
. In one of the few field tests of the behavior of triploid fish released into the natural environment, triploid adult Atlantic salmon migrated back from the ocean to natal freshwaters at a much lower rate than did control salmon, thus reducing the population that could attempt to mate with wild fish (Cotter et al., 2000)
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From page 141... ...
. This becomes a concern under the likely scenario that biotechnology companies will sell only sterile transgenic fish eggs or fry to farmers.
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From page 142... ...
. Applying this production cycle to transgenic fish involves developing an all-female line of transgenic fish, then fertilizing transgenic eggs with milt from the sex-reversed females, and inducing triploidy on the newly fertilized eggs.
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From page 143... ...
Strengths The combination of all-female lines with triploidy circumvents the problem of incomplete sterilization in triploid males. Protocols are well established in some commercially important species and should be fairly easy to develop for others.
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From page 144... ...
. · All accessible ecosystems lack wild relatives, thus precluding gene flow from any fertile genetically engineered organisms into wild populations.
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From page 145... ...
Additional areas of expertise and local knowledge could be necessary, depending on the case. Gene Blocking and Gene Knockout The growing base of information about the function of specific animal genes, inducible promoters, and ways of blocking gene expression or of completely knocking out target genes could be harnessed to disrupt reproduction or survival of escaping fish and shellfish.
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From page 146... ...
Other research has aimed, from the outset, at developing bioconfinement techniques for transgenic fish and shellfish (e.g., Thresher et al., 1999)
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From page 147... ...
Strengths The ability to repress gene blockage allows normal performance of animals while they are in captivity. This method also allows for building in multiple redundancy by stacking sequences to block expression of different essential genes and at different stages of development.
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From page 148... ...
Data on effectiveness await completion of development of transgenic fish lines with stable inheritance and expression of a sterile feral genetic construct (R. Thresher, CSIRO Marine Research, personal communication, May 20, 2003)
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From page 149... ...
Strengths Homologous recombination is not necessary for function, only knowledge of the sequence of the target genes in the target organisms. Weaknesses Experiments using RNAi in fish have not demonstrated sufficient specificity of target gene inhibition, and RNAi might not be suitable as a mechanism for knockdown or knockout of target gene expression .
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From page 150... ...
Finally, the analogues could prove environmentally unstable and thereby present a hazard to nontransgenic organisms. Gene Knockout A target gene could be inactivated by knockout processes similar to those used to produce transgenic knockout mice.
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From page 151... ...
. Naturally Sterile Interspecific Hybrids There are few well-documented examples of sterile hybrids among fish and shellfish.
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From page 152... ...
However, concerns about the adverse effects of escapees on wild relatives would apply to either or both parental species, depending on their co-occurrence in accessible ecosystems. Such concern would arise either because some undetected percentage of escapees is not functionally sterile or because sterile individuals enter into normal courtship behavior and can therefore disrupt the reproductive success of wild mates.
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From page 153... ...
Gene regulation strategies aimed at biological control of pest or nuisance species are not appropriate for bioconfinement. Consider for example the research under way in Australia to develop transgenic fish lines that bear a "daughterless gene" construct as a strategy for eradication of alien, nuisance fish species that have invaded river systems (CSIRO, 2002; Nowak, 2002; Woody, 2002)
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From page 154... ...
. Additionally, many of the most effective methods require so much time or such destructive testing of target organisms that it would be unfeasible for a program involving large numbers of transgenic organisms to be biologically confined.
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From page 155... ...
indicating that reorientation of this approach to achieve bioconfinement of transgenic insects (rather than to control pest insects) would be possible for a broad range of species.
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From page 156... ...
Thus the use of SIT in bioconfinement must consider the response of the target organism to the sterilizing method. Transgenic Sterile Insects Gene transfer also has been proposed as a way to produce sterile insects for biological control that would improve on the traditional SIT approach and replace the use of radiation or other mutagens to induce sterility (Alphey, 2002; Alphey and Andreasen, 2002; Thomas et al., 2000; Wimmer, 2003)
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From page 157... ...
One strategy involves developing transgenic traits for inducible genetic sterility. An example demonstrated in fruit flies involves a transgene-based dominant embryonic lethality system that can generate large quantities of competitive but sterile insects (Horn and Wimmer, 2003)
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From page 158... ...
Perhaps such biological factory insects could be rendered flightless or incapable of long-range dispersal by use of a flight-defective mutation, such as the long-known recessive Drosophila gene vg, which results in flightless insects. Alternatively, technology for gene blocking or gene knockout in development for bioconfinement of transgenic fish and shellfish might be developed to prevent reproduction or postescape survival of industrial transgenic insects.
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