Recombinant Adenovirus in Neurobiology - Viral Vector Approaches in Neurobiology and Brain Diseases - page 11

construct, one can control the expression of the target gene to a
specifi c cell type [ 5 , 6 ]. On the other hand, administration of
recombinant adenovirus containing antisense sequences or siRNAs
of a target gene can reduce the expression of the gene in the spe-
cifi c brain region and may be cell type specifi c [ 7 , 8 ]. Administration
of recombinant adenovirus containing sequence for inducing pro-
tein, such as Cre DNA recombinase, into inducible knockout or
knock-in mice with same inducible system, such as a Cre-loxP, one
can activate the inducible systems in specifi c brain regions and at
specifi c developmental periods [ 9 , 10 ]. This approach can be used
to not only conduct inducible knockout or knock-in in selected
brain regions but also can avoid the need to cross-breed the induc-
ible knockout or knock-in mice with Cre transgenic mice that
could be lethal. Furthermore, delivery of a gene, which is a neuro-
nal tracer, such as barley lectin or tetanus toxin fragment C, to
specifi c brain regions using recombinant adenovirus greatly facili-
tates studies on anatomic neurocircuitries because the tracers can
be controlled by promoters to selectively express in the neurons of
interest [ 11 ].
One of the most commonly used recombinant adenoviral sys-
tems is the AdEasy system [ 12 - 14 ]. The AdEasy system contains
shuttle vectors and an AdEasy-1 viral vector. Compared to other
viral systems, the AdEasy is a simple and highly effi cient system.
It contains two vectors, a shuttle vector and a viral vector. Both
vectors can be amplifi ed in Escherichia coli , which makes production
of the construct and recombinant the virus easier. In the AdEasy-1
vector, E1 and E3 domains are deleted. Therefore, the toxicity of
the AdEasy-1-derived recombinant adenovirus is reduced.
However, the toxicity of recombinant adenovirus is higher than
other viral systems such as adeno-associate virus. Another feature
of the adenovirus is limited spread of the virus, which is particularly
useful for manipulating gene expression in selective brain regions
[ 6 ]. In contrast, the recombinant adenovirus is not suitable for
alterations of gene expression in the whole brain. Since recombi-
nant adenovirus is not able to proliferate, it dies when the cells
propagate. Thus, the infection of proliferative cells, such as astro-
cytes, usually last for 2-3 weeks. However, because neurons do not
proliferation, the viral infection lasts much longer in neurons [ 6 ].
Therefore, although recombinant adenovirus has similar infection
effi ciency for astrocytes and neurons, most infected cells are neurons
when a long-term treatment approach is used. Furthermore, recom-
binant adenoviruses induce only transient expression. It should be
noted with caution that the protein expressed by the virus may not
undergo physiological and pathological processes similar to endog-
enous proteins. This is especially important for posttranslational
modifi cations, which may not occur in virally expressed proteins in
cell lines. All together, recombinant adenovirus is a useful tool
for neurobiological research once we understand the features of
the AdEasy systems.