Biology Reference
In-Depth Information
Baculoviruses infect many pest insects and several have been used as biological
pesticides, including
Autographa californica
NPV and
Lymantria dispar
NPV (
Shuler
et al. 1994
). These, and the
Bombyx mori
NPV, were exploited as vectors to carry
exogenous DNA into insect cells (
Miller 1988
,
Iatrou and Meidinger 1990
,
Yu et al.
1992
). Baculovirus vectors can produce a high level of commercially important pro-
teins in insect cell cultures (
Frommer and Ninnemann
1995,
Jones and Morikawa
1996
). The host range of baculovirus vectors has been found to include human
liver cells, suggesting that baculoviruses could be used for gene therapy in humans
(
Hofmann et al. 1995
). Recombinant baculoviruses can integrate into Chinese ham-
ster ovary chromosomes in cell cultures, suggesting they could be used as gene vec-
tors for transforming mammals in a stable manner (
Merrihew et al. 2001
).
Densonucleosis viruses (Parvoviridae) are linear single-stranded DNA mol-
ecules that apparently are restricted to arthropods and can be used to deliver
genes into mosquitoes for laboratory studies of gene expression. Densoviruses
also might be used for biological control programs directed against mosquitoes
(
Beaty and Carlson 1997, Carlson et al. 2000
).
Retroviral vectors were developed by genetically modifying the Moloney
murine leukemia virus so that it contains the G-envelope protein from vesicu-
lar stomatitis virus (
Burns 2000
). These retroviral vectors have a very wide host
range (are pantropic), but are considered to be stable once inserted into the
host genome because they lack the genetic information needed to propagate.
These vectors have been evaluated for human gene therapy and can be used to
transform fish, cows, clams, and amoebae, as well as lepidopteran and dipteran
cells (
Burns 2000
). The viruses have been used to study promoter function and
regulation in insect cells (
Matsubara et al. 1996, Jordan et al. 1998, Burns 2000
).
Silk moth embryos infected with pseudotyped retroviral particles carrying the
GFP construct yielded larvae that contained these viral vector sequences, indicat-
ing the virus integrated into the genome (
Komoto et al. 2000
).
The
gypsy
element in
D. melanogaster
is an infectious retrovirus; it was the
first retrovirus to be identified in invertebrates (
Kim et al. 1994, Bucheton 1995
).
gypsy
normally is repressed (prevented from moving) by a gene in
Drosophila
called
flamenco.
. Apparently,
gypsy
elements invaded
D. melanogaster
a long
time ago and
D. melanogaster
survived the invasion because variants of the
fla-
menco
gene were able to suppress the activity of the invading
gypsy
(
Pelisson
et al. 1997
). This is a fine example of the ability of insects to evolve resistance to
invading nucleic acids (including TEs) that cause genetic damage.
Alphaviruses (Togaviridae) have a single-stranded RNA genome and have been
genetically engineered as expression vectors (
Beaty and Carlson 1997
). These
