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Although there are other, non-array methods for analyzing gene expression, such as
serial analysis of gene expression (SAGE), the simplicity of the oligonucleotide
approach makes it the most attractive option for the gene expression profi ling.
Important applications are in drug discovery, a fi eld that is now fl ooded with poten-
tial targets. Microarrays will play an essential role in overcoming this obstacle in
both target identifi cation and in the long road of drug discovery and development.
Two important therapeutic areas for gene expression profi ling using microarrays are
cancer and neurological disorders.
Analysis of Single-Cell Gene Expression
Analysis of single-cell gene expression promises a more precise understanding of
human disease pathogenesis and has important diagnostic applications. Single cell
isolation methods include fl ow cytometry cell sorting and laser capture microdis-
section. Besides the gene expression analysis, the following nucleic acid amplifi ca-
tion methods are suitable for single-cell analysis:
- Single cell phenotyping
- Homomeric tailed PCR, which allows unbiased amplifi cation of RNA
- RNA amplifi cation
Gene expression analysis of single cells is providing new insights into disease
pathogenesis, and has applications in clinical diagnosis. Molecular signatures of
some diseases can best be discerned by analysis of cell subpopulations. Studies in
disease-relevant cell populations that identify important mRNA (and protein) differ-
ences between health and disease should allow earlier diagnosis, better therapeutic
intervention and more sensitive monitoring of treatment effi cacy. This will facilitate
the developed of personalized medicine based on the molecular signatures of the
diseased cell population.
Current assays for gene expression destroy the structural context. By combining
advances in computational fl uorescence microscopy with multiplex probe design,
expression of many genes can be visualized simultaneously inside single cells with
high spatial and temporal resolution.
Gene Expression Profi ling Based on Alternative RNA Splicing
RNA splicing is an essential, precisely regulated process that occurs after gene tran-
scription and before mRNA translation. A gene is fi rst transcribed into a pre-mRNA,
which is a copy of the genomic DNA containing intronic regions destined to be
removed during pre-mRNA processing (RNA splicing), as well as exonic sequences
that are retained within the mature mRNA. During splicing, exons can either be
retained in the mature message or targeted for removal in different combinations to
2 Molecular Diagnostics in Personalized Medicine