Veeraiah Bodepudi

High-density Hapten Labeling and HRP Conjugation of Oligonucleotides for Use as In Situ Hybridization Probes to Detect mRNA Targets in Cells and Tissues

Oligonucleotides that carry a detectable label can be used to probe for mRNA targets in in situ hybridization experiments. Oligonucleotide probes (OPs) have several advantages over cDNA probes and riboprobes. These include the easy synthesis of large quantities of probe, superior penetration of probe into cells and tissues, and the ability to design gene- or allele-specific probes. One significant disadvantage of OPs is poor sensitivity, in part due to the constraints of adding and subsequently detecting multiple labels per oligonucleotide. In this study, we compared OPs labeled with multiple detectable haptens (such as biotin, digoxigenin, or fluorescein) to those directly conjugated with horseradish peroxidase (HRP). We used branching phosphoramidites to add from two to 64 haptens per OP and show that in cells, 16-32 haptens per OP give the best detection sensitivity for mRNA targets. OPs were also made by directly conjugating the same oligonucleotide sequences to HRP. In general, the HRP-conjugated OPs were more sensitive than the multihapten versions of the same sequence. Both probe designs work well both on cells and on formaldehyde-fixed, paraffin-embedded tissues. We also show that a cocktail of OPs further increases sensitivity and that OPs can be designed to detect specific members of a gene family. This work demonstrates that multihapten-labeled and HRP-conjugated OPs are sensitive and specific and can make superior in situ hybridization probes for both research and diagnostic applications.

High-specificity single-tube multiplex genotyping using Ribo-PAP PCR, tag primers, alkali cleavage of RNA/DNA chimeras and MALDI-TOF MS.

Here, we describe a high‐throughput, single‐tube, allele‐specific ribonucleotide analog pyrophosphorolysis‐activated polymerization (ribo‐PAP) PCR multiplex genotyping and resequencing method. An RNA/DNA chimeric PCR product is generated using genomic DNA as starting template, a panel of allele‐selective 5′‐tagged primers, a reverse primer, one nucleotide in the ribo‐form (90–100%), the other nucleotides in the deoxy‐form, a DNA polymerase capable of incorporating ribonucleotides, a suitable buffer and thermal cycling. The RNA/DNA chimeric PCR products are fragmented by treatment with alkali and analyzed by mass spectrometry. All allele‐selective primers have a 5′ repetitive motif where each repeat unit has a unique, distinct mass upon reverse copying and alkali fragmentation. The mass of the complement repeat fragment or flag identifies the primer or primers that were recruited in the ribo‐PAP PCR. The method readily identifies homozygous and heterozygous positions in simplex or duplex ribo‐PAP PCR. Many different tags can be analyzed simultaneously. The assay can genotype several SNPs in a single tube. It thus constitutes the simplest genotyping protocol with multiplex analysis. This novel genotyping and resequencing protocol was applied to different genomic loci: NOS1 and H19 in 30 individuals in simplex ribo‐PAP PCR and at two SLCO1B1 loci in 95 individuals in duplex ribo‐PAP PCR.