Biology Reference
In-Depth Information
a single
P
inserts into a gene and causes a visible mutation, facilitates the iden-
tification and cloning of genes from
Drosophila
.
P
-element vectors repair gaps
left in chromatids when
P
elements excise, which offers the possibility of insert-
ing exogenous DNA into targeted, rather than random, sites in the
Drosophila
chromosome.
Many drosophilid species have inactive forms of
P
in their genomes, which are
suppressed by several mechanisms to reduce the deleterious effects transposi-
tion imposes on individuals and populations. The long-term survival of TEs such
as
P
may require that it move horizontally into new species.
P
-element vectors cannot be used to transform insects other than
Drosophila
,
but other TEs, including
Hermes
,
minos
,
hobo
,
piggyBac
and
mariner
, have been
engineered as vectors. They can transform a variety of insect species, providing
tools with which to insert exogenous genes into both pest and beneficial insects
with the goal of improving pest-management programs. Risk issues relating to
use of TE vectors include the possibility of horizontal transfer to nontarget spe-
cies and a lack of stability of the transgene. Also, transformation frequencies are
usually
<
5% and insertions can occur in regions of the genome that result in low
levels of expression.
Recently, other techniques have been developed to insert genes into specific
sites within the genome or to replace a genome sequence with an inserted one
or to inhibit expression of endogenous genes. These include zinc-finger nucle-
ases (ZFNs) and transcription activator-like effectors (TALEs). Homing endo-
nucleases (or meganucleases) also can result in gene mutations/insertions. RNA
interference (RNAi) can be used to reduce transcription of specific genes, at least
temporarily, and nanotechnology methods are being studied as tools to deliver
RNAi or to insert novel genes. It remains to be determined whether these new
methods will result in more-stable and effective transformations of insects for
pest-management programs.
9.2 Introduction
The
P
element first was genetically modified to serve as a vector of exogenous
DNA in 1982 (
Rubin and Spradling 1982, Spradling and Rubin 1982
). A variety
of different
P
-element vectors are used routinely to introduce exogenous DNA
into
D. melanogaster
.
P
-mediated transformation of
D. melanogaster
has revo-
lutionized how geneticists study gene structure, function, regulation, position
effects, dosage compensation, and development.
P
-mediated transformation
allows geneticists to decipher the genetic basis of behavior, development, and
sex determination in
Drosophila
, as is described in Chapters 10 and 11.
