Biology Reference
In-Depth Information
active TEs or inactive TE vectors (
Petrov et al. 1995
). The safest course might be
to remove any introduced TE vector sequences from a transgenic strain before
its
permanent
release into the environment to reduce the probability that the
transgene will move, either within the strain or horizontally between different
populations or species.
Elements other than
P
and
mariner
also move horizontally.
Jordan et al.
(1999)
showed that a long terminal repeat retrotransposon (a different class of
element than the
P
and
mariner
elements) in the
D. melanogaster
group species
moved into
D. willistoni
, perhaps within the past 100-200 years.
Insect viruses could mediate HT of DNA. The
piggyBac
element was discovered
embedded within the genome of a baculovirus (
Fraser 2000
) and another
Tc1
-like
transposon was found in the
Cydia pomonella
granulovirus (
Jehle et al. 1998
). If
HT of transgenes by viruses were to occur in the field, there is no guarantee that
genes inserted into a particular species would remain within that species.
HT might even occur when DNA is eaten. Although most consumed DNA is
degraded over time in the gut, it may not happen for several days (
Schubbert
et al. 1997, 1998
). Bacteriophage DNA fed to mice can persist in fragmented
form in the gut, can penetrate the intestinal wall and reach the nuclei of leu-
kocytes, spleen, and liver cells (
Schubbert et al. 1998
). Fetal and newborn prog-
eny of female mice fed such DNA during pregnancy had the phage DNA in
various organs. Furthermore, the phage DNA was located in nuclei and associ-
ated with chromosomes, although the DNA had not integrated (
Schubbert et al.
1998
). Such an association of DNA with the chromosomes could affect normal
gene function.
Hohlweg and Doerfler (2001)
fed mice soybean leaves containing
a specific gene and analyzed its fate. This experiment provided a more natural
delivery system than feeding naked DNA. The results indicated that DNA in soy-
bean leaves was found less frequently in mice tissues than when naked DNA was
fed, in part because the amount of DNA was reduced by
≈
5 orders of magnitude
(
Hohlweg and Doerfler 2001
).
Genetic engineering of insect gut symbionts might allow the movement of
the inserted genes between the many types of microorganisms found within the
insect gut (
Watanabe and Sato 1998, Watanabe et al. 1998
).
Enterobacter cloacae
,
a bacterium found in the guts of insects, and
Erwinia herbicola
, a bacterium that
grows on the surface of plants, grow in the guts of silk moth larvae and exchange
genetic information via plasmids at very high rates (
Watanabe and Sato 1998,
Watanabe et al. 1998
). The bacteria containing new genetic information were
found in insect feces, suggesting that this method of HT is a frequent event in
