Biology Reference
In-Depth Information
Figure 9.4
Two
P
-element vectors, mutator (A) and jumpstarter (B), were developed to facilitate
insertion of a single
P
element to identify and clone genes in
D. melanogaster
. Jumpstarter encodes
transposase and can therefore mobilize mutator. Mutator is able to transpose and carries ampicillin
and neomycin resistance genes to facilitate identification and subsequent cloning of the
Drosophila
gene into which it has inserted. (Modified from
Cooley et al. 1988
.)
structure of the mutator element facilitates identifying and cloning genes
because it carries two selectable markers.
9.8.2 Expressing Exogenous Genes
Genetic engineering techniques permit the expression of exogenous genes
in a variety of organisms, and the availability of a transformation method for
Drosophila
makes it possible to express interesting genes in this insect. For
example,
Rancourt et al. (1990)
obtained expression in
D. melanogaster
of two
antifreeze-protein genes isolated from the Atlantic wolfish,
Anarhichas lupus
.
The two genes were cloned into a
P
vector with
Drosophila
yolk-protein gene
promoters. These highly active promoters were expressed in
Drosophila
females
shortly after eclosion and remained active for several weeks. Transformed adult
Drosophila
females produced 1.5-5mg/ml of antifreeze protein in their hemo-
lymph. The antifreeze activity of the purified protein was determined by mea-
suring freezing point depression and had full biological activity.
9.8.3 Evaluating Position Effects
Transposon jumping
can be used to move stably inserted
P
elements lacking
transposase to other sites within the genome. This allows researchers to explore
the effects of position on gene expression. To induce jumping, embryos from a
transformed strain are injected with helper plasmids that transcribe transposase.
The transposase interacts with the terminal repeats of the stably inserted
P
con-
struct, causing it to transpose to a new site. The gene located within the P vec-
tor experiences a new genomic environment that may modify expression levels.
The helper element does not integrate, so the new strain should be stable until
transposase is again supplied.
