Biology Reference
In-Depth Information
Stable transformation of the nuclear genome involves incorporating the
genetic information into the germ line (ovaries and testes) so that the new
genetic information is transmitted to succeeding generations (
=
transgenesis).
Several approaches have been successful in inserting exogenous nucleic acids
into the genomes of insects (
Table 14.3
). Typically, multiple transgenic lines are
developed and evaluated to determine which are most fit and stable in the
laboratory; such evaluations should be conducted in a manner to preclude acci-
dental release into the environment by using appropriate containment condi-
tions and procedures (
Hoy et al. 1997, Young et al. 2000
,
National Academy of
Sciences 2004
). If laboratory tests indicate that the transgenic strain is fit and
the trait is stably and appropriately expressed, the transgenic strain(s) may be
evaluated in greenhouses or small field plots to confirm their efficacy and fit-
ness under more-natural conditions (
Table 14.2
).
The goals of genetic manipulation of the nuclear genomes of pest and benefi-
cial insects are different, although most of the steps are similar (
Table 14.2
). The
goal is to
reduce
or eliminate the pest population, or its impact; by contrast, the
goal is to
enhance
or increase the population of beneficial arthropods, or their
impact, in the field.
14.5 What Genetic Modification Methods are Available?
14.5.1 Transposable-Element (TE) Vectors and Transgenesis
Inserting nucleic acids into insects can be accomplished using several differ-
ent techniques (
Table 14.3
). If the inserted DNA is incorporated into the chro-
mosomes in the cells that give rise to the ovaries and testes, the new genetic
material could be transmitted faithfully and indefinitely to successive genera-
tions (stable germ-line transformation). However, not all gene insertions remain
stable due to gene silencing, DNA-repair mechanisms, or instability due to the
movement of the transposable-element (TE) vector.
Initial research on stable transformation methods were accomplished with
Drosophila melanogaster
when it was discovered that the
P
element could be
genetically manipulated to serve as a vector to carry foreign genes into the
chromosomes of germ-line cells (
Rubin and Spradling 1982, Spradling and Rubin
1982
, see Chapter 9). The genes carried by the
P
-element vector became stably
integrated into the chromosomes of
D. melanogaster
and were expressed. This
served as the model for several years but, ultimately, the
P
element failed to
transform insects other than
Drosophila
species. As a result other TEs, such as
Hermes
,
hobo
,
mariner
,
Minos
and
piggyBac
, were isolated from insects and
genetically modified for use as vectors (
Atkinson et al. 2001
).
