Biology Reference
In-Depth Information
microinjection of TE vectors and other vectors into dechorionated insect eggs
or microinjection of plasmids directly into the testes of males or the abdomen
of female mites or insects (maternal microinjection). Less frequently, DNA has
been delivered by soaking eggs in DNA, using sperm to carry foreign DNA into
eggs of the honey bee, by using microprojectiles (gene gun technology) to insert
DNA into insect eggs, electroporation of DNA into insect eggs, and transplant-
ing nuclei and cells. Future methods might involve inserting artificial chromo-
somes into the insect genome, especially if multiple genes are to be inserted.
14.7 What Genes are Available?
Cloned DNA can be isolated from the same or other species. It is technically fea-
sible to insert genes from microorganisms into arthropods and have the DNA
transcribed and translated, although coding sequences isolated from microor-
ganisms must be attached to promoters (controlling elements) and other regu-
latory sequences derived from a eukaryotic organism so that the gene can be
expressed in insects. The regulatory sequences determine when a gene will be
transcribed, at what level, in what tissues, and how long the messenger RNA can
be used for translation. Considerable research has been conducted to identify
regulatory sequences that regulate genes in specific tissues.
It also may be possible to isolate a gene from the species being manipulated,
alter it, and reinsert it into the germ line, although this approach has not yet
been attempted in insects other than
Drosophila
. This approach has received
increased interest in plant breeding using recombinant DNA methods because it
decreases concerns about risks. The complete sequence of genomes from multi-
ple arthropod species (see Chapter 7) increases our ability to identify interesting
genes in other arthropods using sequence similarity of conserved regions.
Many relevant traits probably are determined by multiple genes, which make
them difficult to manipulate at present. Inserting traits determined by multiple
genes into an insect by recombinant DNA methods has not been achieved, but
there are several methods by which several foreign genes can be introduced
into a transgenic plant that might be adapted for use in insects (
Halpin et al.
2001, Hunt and Maiti 2001
).
14.8 Why are Regulatory Signals Important?
Genes consist of coding segments that determine the amino-acid sequences in
the enzyme or structural proteins produced. However, whether a protein-coding
region is transcribed and translated in a specific tissue is determined by regula-
tory sequences in the DNA, including promoters, enhancers and multiple types
