time of mRNA extraction, this is known as a cDNA library. A synthetic probe is
used to select only the growth hormone cDNA for cloning.
The third step is extraction of the growth hormone gene itself. Within the egg
cell, there is a strong probability that the entire introduced gene will be expressed,
rather than the cDNA, which lacks intron. First, the entire genome DNA is extracted
from body tissues such as corpuscles or muscles polymeric state, and restriction
enzymes are used to separate it into fragments, each of which is recombined with a
bacillus bacterium or phage and cloned. This is known as a chromosomal DNA
library, as it is believed to contain all genes on the chromosome. A more precise
method of selecting the growth hormone gene involves the use of a cDNA probe
containing a sequence complementary to the entire information section. Cloned
growth hormone genes may be microinjected into the egg cell as it is or in combination with a suitable promoter. The gene’s introduction into the host rainbow
trout genome, its expression, and its transmission to future generations must be
individually verified.
Next, we will consider what genes may be introduced to produce particular kinds
of fish. In traditional cross-breeding approaches, available genes have been limited
to those within species that are the same or closely related. With gene introduction,
it is possible for any gene from any organism to be introduced according to a set
method. In other words, it becomes possible to use the genetic resources of all
20,000 or so species of fish, or of the millions of species of organisms living on
Earth today.
In some cases, genes already possessed by the fish, or something similar, are
introduced and their activities amplified with an emphasis on specific beneficial or
economic properties (such as growth hormone genes). In others, entirely new genes
are introduced to transfer an outstanding capability specific to one fish intact to
another (as with genes for flounder anti-freezing proteins or carp a-globin). Both
are crucial for breeding.
Introduction of growth hormone genes was touched off by research conducted in
1982, when Richard Palmiter and other U.S. researchers introduced rat growth
hormone genes to a fertilized mouse egg to create a “super mouse” nearly twice the
weight of a normal mouse. In the future, genes from fish will be used rather than
genes from previously cloned mammals. This approach is beneficial in terms of
regulating gene expression in the host and the physiological activity of the final
peptide hormone product.
Anti-freezing proteins in the blood of flounders allow them to live in Arctic
Ocean where their blood would otherwise freeze. Attempts are now under way to
introduce those genes into salmon to increase the range of regions in which they can
be farmed.
Salmon and trout are vulnerable to oxygen deficiency, whereas carp are stronger.
This stems from differences in the structure of their hemoglobin (a protein that
transports oxygen in the blood), and in its globin molecule subunits. By introducing
carp globin genes into rainbow trout, it may be possible to significantly increase the
latter’s respiratory capabilities—allowing them to be raised in non-flowing waters
—and produce rainbow trout that are easy transported.
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4 Fish Breeding and Biotechnology
used to select only the growth hormone cDNA for cloning.
The third step is extraction of the growth hormone gene itself. Within the egg
cell, there is a strong probability that the entire introduced gene will be expressed,
rather than the cDNA, which lacks intron. First, the entire genome DNA is extracted
from body tissues such as corpuscles or muscles polymeric state, and restriction
enzymes are used to separate it into fragments, each of which is recombined with a
bacillus bacterium or phage and cloned. This is known as a chromosomal DNA
library, as it is believed to contain all genes on the chromosome. A more precise
method of selecting the growth hormone gene involves the use of a cDNA probe
containing a sequence complementary to the entire information section. Cloned
growth hormone genes may be microinjected into the egg cell as it is or in combination with a suitable promoter. The gene’s introduction into the host rainbow
trout genome, its expression, and its transmission to future generations must be
individually verified.
Next, we will consider what genes may be introduced to produce particular kinds
of fish. In traditional cross-breeding approaches, available genes have been limited
to those within species that are the same or closely related. With gene introduction,
it is possible for any gene from any organism to be introduced according to a set
method. In other words, it becomes possible to use the genetic resources of all
20,000 or so species of fish, or of the millions of species of organisms living on
Earth today.
In some cases, genes already possessed by the fish, or something similar, are
introduced and their activities amplified with an emphasis on specific beneficial or
economic properties (such as growth hormone genes). In others, entirely new genes
are introduced to transfer an outstanding capability specific to one fish intact to
another (as with genes for flounder anti-freezing proteins or carp a-globin). Both
are crucial for breeding.
Introduction of growth hormone genes was touched off by research conducted in
1982, when Richard Palmiter and other U.S. researchers introduced rat growth
hormone genes to a fertilized mouse egg to create a “super mouse” nearly twice the
weight of a normal mouse. In the future, genes from fish will be used rather than
genes from previously cloned mammals. This approach is beneficial in terms of
regulating gene expression in the host and the physiological activity of the final
peptide hormone product.
Anti-freezing proteins in the blood of flounders allow them to live in Arctic
Ocean where their blood would otherwise freeze. Attempts are now under way to
introduce those genes into salmon to increase the range of regions in which they can
be farmed.
Salmon and trout are vulnerable to oxygen deficiency, whereas carp are stronger.
This stems from differences in the structure of their hemoglobin (a protein that
transports oxygen in the blood), and in its globin molecule subunits. By introducing
carp globin genes into rainbow trout, it may be possible to significantly increase the
latter’s respiratory capabilities—allowing them to be raised in non-flowing waters
—and produce rainbow trout that are easy transported.
104
4 Fish Breeding and Biotechnology