To induce powerful expression without specifying a time or site, an effective
approach is to use a virus such as simian virus 40 (SV40), which is isolated from
monkeys, or respiratory syncytial virus (RSV). Powerful promoters that allow
expression to be controlled may also be used from metallothionein or heat shock
protein genes.
3. Transmission to Later Generations (Establishing a Transgenic Line)
One introduced to a host genome, the gene is transmitted to future generations
through eggs of sperm. Not all of the offspring will possess the gene, however. The
genes are not introduced simultaneously at the same sites in two homologous
chromosomes; rather, gametes with and without the genes form after meiosis.
Transfer of genes microinjected into a fertilized egg typically takes place after the
second cell stage; often, cells in the parents’ bodies (including pre-meiosis reproductive cells) are separated into those with and without the genes, which form a
kind of mosaic.
To establish a line where foreign genes are constantly being transmitted to all
descendants, it is necessary to first create organisms in which those genes form a
homo junction on the chromosome. These may be obtained through gynogenesis in
the initial transgenic female, or similarly through androgenesis in the male.
4.4.2 Examples of Applications
The previous sections have given a sequential account of the basic techniques
needed for fish breeding. In contrast with chromosome or cell manipulation, these
basic techniques hold no significance at all on their own. Rather, they are mere
constituents in the technical system of the single greatest example of application,
namely the creation of transgenic fish.
For this reason, the explanation in this section will consider the introduction of
tuna growth hormone genes into a rainbow trout as an example of application
(Fig. 4.14). The purpose of this research is to significantly promote the trout’s
growth and create a fish that is as large and flavorful as tuna through marine culture.
The entire system consists of modification of growth hormone genes, a process
that consists of three stages.
First, a specific base sequence is located in the growth hormsone gene, and a
probe is created with a complementary oligonucleotide (a DNA fragment consisting
of dozens of bases). This requires extraction and purification of growth hormone (a
protein molecule) from the tuna’s pituitary gland (an organ for hormone production) and analysis of its amino acid sequence. By estimating the corresponding
DNA base sequence on the genetic code, it is possible to identify the major
sequences of the tuna’s growth hormone gene. A very specific sequence is then
selected and a DNA fragment consisting of 20 to 50 bases is artificially synthesized
with a synthesizer. Once it has been labeled with
32 P, it is now a probe.
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approach is to use a virus such as simian virus 40 (SV40), which is isolated from
monkeys, or respiratory syncytial virus (RSV). Powerful promoters that allow
expression to be controlled may also be used from metallothionein or heat shock
protein genes.
3. Transmission to Later Generations (Establishing a Transgenic Line)
One introduced to a host genome, the gene is transmitted to future generations
through eggs of sperm. Not all of the offspring will possess the gene, however. The
genes are not introduced simultaneously at the same sites in two homologous
chromosomes; rather, gametes with and without the genes form after meiosis.
Transfer of genes microinjected into a fertilized egg typically takes place after the
second cell stage; often, cells in the parents’ bodies (including pre-meiosis reproductive cells) are separated into those with and without the genes, which form a
kind of mosaic.
To establish a line where foreign genes are constantly being transmitted to all
descendants, it is necessary to first create organisms in which those genes form a
homo junction on the chromosome. These may be obtained through gynogenesis in
the initial transgenic female, or similarly through androgenesis in the male.
4.4.2 Examples of Applications
The previous sections have given a sequential account of the basic techniques
needed for fish breeding. In contrast with chromosome or cell manipulation, these
basic techniques hold no significance at all on their own. Rather, they are mere
constituents in the technical system of the single greatest example of application,
namely the creation of transgenic fish.
For this reason, the explanation in this section will consider the introduction of
tuna growth hormone genes into a rainbow trout as an example of application
(Fig. 4.14). The purpose of this research is to significantly promote the trout’s
growth and create a fish that is as large and flavorful as tuna through marine culture.
The entire system consists of modification of growth hormone genes, a process
that consists of three stages.
First, a specific base sequence is located in the growth hormsone gene, and a
probe is created with a complementary oligonucleotide (a DNA fragment consisting
of dozens of bases). This requires extraction and purification of growth hormone (a
protein molecule) from the tuna’s pituitary gland (an organ for hormone production) and analysis of its amino acid sequence. By estimating the corresponding
DNA base sequence on the genetic code, it is possible to identify the major
sequences of the tuna’s growth hormone gene. A very specific sequence is then
selected and a DNA fragment consisting of 20 to 50 bases is artificially synthesized
with a synthesizer. Once it has been labeled with
32 P, it is now a probe.
102
4 Fish Breeding and Biotechnology