Use of complex oligonucleotide libraries for concurrent high-resolution fluorescence imaging of both DNA and RNA in various sample types

Abstract

Fluorescence in situ Hybridization (FISH) is a powerful technique for determining the localization specific nucleic acid sequences within individual cells. Previously, the use of FISH has often been dependent upon access to cloned template DNA for the generation of probes, which can be difficult if clones for specific regions are unavailable, or if the genomic region of interest contains repetitive and/or other problematic sequences. We have developed the ability to chemically synthesize DNA in massively parallel reactions, which we have used to produce libraries of oligonucleotides up to 200 bases in length that can be utilized for the generation of FISH probes. The sequences of the oligonucleotides in these libraries are selected in silico using empirically determined criteria so as to avoid repetitive elements or regions homologous to other non-targeted loci. We have found that these oligonucleotide library-derived FISH probes can detect human genomic regions as small as 1.8 kb and as large as whole chromosomes in both metaphase and interphase cells, using the same simple assay protocol. Because of the inherent flexibility in our probe design methods, we can readily visualize regions rich in repeats and/or GC content. We have also used these oligonucleotide library-derived FISH probes to detect the localization of a variety of both coding and non-coding RNAs in fixed tissue culture cells and formalin-fixed paraffin-embedded tissue sections, using both conventional fluorescence and structured illumination microscopy. Simultaneous hybridization of FISH probes labeled with different fluorophores enables visualization of multiple sequences at once. Using probes designed specifically to transcribed vs. non-transcribed regions has enabled the simultaneously detect DNA and RNA from the same locus, or from two different loci, in the same FISH assay. The ability to generate high performance FISH probes using chemically synthesized oligo libraries that can simultaneously detect DNA and RNA yields a valuable tool for studies of how localization of specific nucleic acids impacts biological function.

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