Biology Reference
In-Depth Information
2010; Gohlmann and Talloen 2009
). Entomologists also use microarrays to eval-
uate gene expression and function. Microarrays are being used to study gene
function in insects, with the goal of understanding development and responses
to environmental cues such as pathogens, temperature, and parasitism (
Gibson
2002, Johnson et al. 2009
). The responses of plants to herbivory by insects can be
studied using microarrays (
Maleck et al. 2000, Schenk et al. 2000, Reymond 2001,
Kempema et al. 2007
).
Each insect cell contains the same DNA, yet each cell and tissue type is dif-
ferent, presumably due to differences in gene activity. Expression microarrays
allow geneticists to determine which genes are on and which are off in specific
cells, tissues, or organisms treated to different environmental conditions. To pro-
duce microarrays, sequences of genes are needed and microarrays can hold the
sequences of an entire genome. Microarrays containing DNA, cDNAs, oligonu-
cleotides (oligos), or proteins allow geneticists to determine the expression level
of a large number of genes in a single experiment. Some microarrays contain-
ing insect genes are commercially available because the community of scien-
tists studying the insect is large and the complete genome has been sequenced
and annotated (for example,
Drosophila
). Companies and core facilities at uni-
versities also produce specific microarrays for fees, upon request. For exam-
ple, Indiana University produces a gene expression microarray for analysis of
the parasitoid
Nasonia vitripennis
, a wasp that has had its genome completely
sequenced (
Werren et al. 2010, Center for Genomics and Bioinformatics 2012
). It
also is possible to make your own microarrays (
Stewart 2000
), although there is
concern that the data obtained from these are less reproducible (
Beisvag et al.
2011
). Microarrays are expensive, but the cost is declining and, relative to the
amount of data that can be obtained from a single experiment, the investment
may be cost-effective.
DNA microarrays are similar to Southern blots in that they rely on comple-
mentary-base pairing between complementary nucleotides for specificity of
the signal (except for protein microarrays). Each spot on a microarray contains
multiple identical strands of DNA (or oligos) and the sequence on each spot
is unique. Each spot should represent one gene, and thousands of spots are
arranged in orderly rows and columns on a solid surface in a precise and unique
manner. Glass, silicon chips, or nylon membranes provide the solid surface and
are approximately the size of a microscope slide (
Lockhart and Winzeler 2000
).
The location and sequence of each spot are recorded. DNA chips or microarrays
can be made with oligonucleotides that are synthesized
in situ
or by conven-
tional synthesis, followed by on-chip immobilization. The array then is exposed
to labeled sample DNA, hybridized, and complementary sequences can be
