Biology Reference
In-Depth Information
viruses, and nonoccluded viruses. Their host range is limited to insects, so the
viruses are considered safe for vertebrates. Likewise, the lepidopteran cells used
are free of human pathogens (
van Oers 2011
). The proteins produced are used
for vaccine preparations or diagnostics or functional studies. The first vaccine
commercially produced in the baculovirus system protects against classical swine
fever (or hog cholera). The first vaccine for human use protects against cervical
cancer, and another product is used to treat prostate cancer.
Most NPVs primarily infect lepidopterans, where they produce nuclear inclu-
sion bodies in which progeny virus particles are embedded. Polyhedrin is the
protein component of the crystalline matrix that protects the viral particles
when they are outside their insect host. Several NPVs have been used as bio-
logical pesticides in pest-management programs, including baculoviruses for
the control of codling moth
Cydia pomonella
on apple, the velvet bean cater-
pillar
Anticarsia gemmatalis
in soybean, and the cotton bollworm
Helicoverpa
armigera
(
van Oers 2011
). Perhaps the most extensively studied baculovirus is
Autographa californica
NPV. It has a relatively broad host range, and the life
cycle of wild-type baculovirus begins when caterpillars eat the protein matrix
(polyhedrin), thereby releasing the virus particles. Virus replication occurs
within host cells, but the protein matrix is not produced early in the infection.
However, when the caterpillar is near death, the virus resumes polyhedrin pro-
duction until
≈
20% of the insect cell proteins consist of polyhedrin.
The
A. californica
nuclear polyhedrosis virus (AcNPV) and the
Bombyx mori
nuclear polyhedrosis virus (BmNPV) have been exploited as vectors to carry
exogenous DNA into insect cells in cell culture or into living silk moth larvae to
produce novel proteins (
Maeda 1989
). The productivity of baculovirus expres-
sion vectors is based on the extremely high efficiency of its polyhedrin gene
promoter. The polyhedrin promoter enables very large amounts of the desired
polypeptides to be produced. The level of expression of foreign gene products
varies, depending on the specific protein being produced.
In principle, any foreign gene could be expressed in the baculovirus-insect cell
expression system. However, cytoplasmic proteins are expressed at higher levels
than secreted glycoproteins, and transmembrane proteins are even more diffi-
cult to produce.
6.9 Expression Microarray Analysis
Microarray analysis of gene expression was adopted and used extensively by
human geneticists who wanted to identify genes important in disease or to
determine what drugs are effective (
Wu et al. 2005; MAQC Consortium 2006,
