Simultaneous detection of different mRNA sequences coding for neuropeptide hormones by double in situ hybridization using FITC- and biotin-labeled oligonucleotides.

Oligonucleotides labeled with FITC or biotin were applied for detection of specific mRNAs in microscopic preparations by in situ hybridization. The oligonucleotides were labeled with one FITC or biotin molecule at the 5' end or with a tail of biotin molecules at the 3' end. The target sequences were mRNAs coding for an ovulation hormone (CDCH) in the caudodorsal cells (CDC) of the pond snail Lymnaea stagnalis and a molluscan insulin-like peptide (MIP) in the light green cells (LGC) of the same organism. The hybridized oligonucleotides were detected either directly after the hybridization procedure by fluorescence microscopy or indirectly after an immunocytochemical procedure to visualize the biotin or FITC moiety. The results indicate that the detectability of the mRNA sequences is at least partially dependent on the accessibility of the target sequences for the immunocytochemical detection systems. The positive hybridization results obtained with oligonucleotides containing different labels enabled us to perform double hybridization experiments for simultaneous detection of CDCH and MIP mRNAs in one tissue section. Using FITC- and biotin-labeled oligonucleotides, we also demonstrated simultaneously different sequences on the same mRNA molecule.