Biology Reference
In-Depth Information
nature. If gut symbionts of pest insects are transformed with antibiotic resistance
genes, these genes might move horizontally to other bacteria within the insect
gut. Transfer of antibiotic resistance genes to pathogens is undesirable because
HT of antibiotic-resistance genes has led to a serious medical crisis. Some human
pathogens are now resistant to almost all available antibiotics.
Whether HT will cause harm would certainly depend on the gene(s) trans-
ferred and its destination. The most serious harm might occur if the TE or viral
vector inserted into germ-line tissues so it could be transmitted to succeed-
ing generations. However, damage also might occur if the elements damaged
somatic tissues; the movement of
mariner
in the soma reduced the lifespan of
Drosophila simulans
males (
Nikitin and Woodruff 1995
). The movement of ret-
roelements into human breast, colon and testicular tissues can induce cancer or
Duchene muscular dystrophy (
Capy et al. 1996
).
Analyses of the role of TEs in the evolution of genomes is undergoing reeval-
uation and it is clear that naturally occurring HT between species has provided
some of the variability upon which evolution has acted, although the ini-
tial event can cause harm (
Plasterk 1993, Krishnapillai 1996, Britten 1997
). It is
unlikely that the presence of a transgene in an arthropod will increase the small
probability that the transgene will be transferred to another species by HT
if
the
TE or viral-vector sequences used could be removed before release into the field.
Even then, however, the probability of HT will not be zero.
Disabled TE vectors probably pose a relatively low risk of HT of the transgene
to other organisms. However, it is possible for an inactivated vector (lacking
transposase or inverted repeats) to become active through a process called
con-
version
.
Peronnet et al. (2000)
showed that conversion could transform an inac-
tive
P
element into an active one through the interaction of three different
P
elements in the genome in a three-step process. Conversion could make a trans-
gene unstable and could, in theory, pose a risk for HT.
The potential risks of using TEs as drivers for inserting useful genes into
arthropod populations should be evaluated carefully on a case-by-case basis.
As noted by
Kidwell and Evgen'ev (1999
), “the transposability of mobile ele-
ments, their potential for rapid, and sometimes massive, amplification in copy
number, their ability to change genomic locations, as well as their propensity for
HT, makes the generalization of results from model organisms far less reliable.
Extrapolation of results from one species to another must therefore be made
with caution.” Models of HT should be examined with care; if inappropriate
assumptions or relevant data are unavailable, models can provide misleading
results (
Caprio and Hoy 1994, 1995
).
