Biology Reference
In-Depth Information
9.17 Conversion of Inactive TE Vectors to Activity
398
9.18 Suppression of Transgene Expression
399
9.19 Other Transformation Methods 399
9.19.1 JcDNV Gene Vectors for Somatic Transformations
401
9.19.2 RNAi for
Drosophila
401
9.19.3 Zinc-Finger Nucleases (ZFNs) 403
9.19.4 Transcription Activator-Like Effector Nucleases (TALENs)
404
9.19.5 Meganucleases (or Homing Endonucleases)
405
9.19.6 Cell-Penetrating Peptides 406
9.19.7 Nanotechnology Approaches
406
9.20 Conclusions 407
General References
407
References Cited
407
9.1 Overview
P
transposable elements (TEs) were genetically modified to serve as vectors for
inserting exogenous DNA into
Drosophila
in 1982 and this tool revolutionized
research on
D. melanogaster
. For the first time, geneticists could insert genes
to study insect development, gene structure, function, regulation and position
effects.
P
elements are found in certain strains (called P) of
D. melanogaster
, but
are lacking in others (M). When P males and M females are crossed, their prog-
eny exhibit a condition called “hybrid dysgenesis” because the
P
elements present
in the chromosomes of the F
1
progeny are no longer prevented from transpos-
ing (or moving). The resultant insertions of
P
elements into new chromosomal
sites result in mutations and sterility (
=
hybrid dysgenesis).
P
elements appear to
have invaded
D. melanogaster
≈
60 years ago from another
Drosophila
species (an
example of horizontal transmission). A mite (Acarina) could have been the mech-
anism by which
P
was transferred into
D. melanogaster
. It was hypothesized that
a parasitic mite obtained
P
elements from the eggs of one
Drosophila
species dur-
ing feeding. Subsequent feeding by this “infected” mite on
D. melanogaster
eggs
might have resulted in the mechanical transfer of
P
elements to
D. melanogaster
and their subsequent spread in field populations around the world. Alternatively,
rare interspecies mating could have allowed
P
to invade
D. melanogaster
.
When
P
-element vectors containing cloned genes are microinjected into early-
stage
Drosophila
embryos (before cellular blastoderm), some of the
P
vectors
integrate into the chromosomes in germ-line tissues. If the newly inserted DNA
is transmitted to the progeny of the injected embryos, stable transformation
has occurred. Multiple lines of putative transformants are produced and evalu-
ated for stability and expression levels of the inserted gene. The location of the
insertion may affect expression levels. Transposon tagging, which occurs when
