The use of 33P-labelled riboprobes for in situ hybridizations: localization of myosin alkali light-chain mRNAs in adult human skeletal muscle.

33P-labelled probes were used to localize the mRNAs coding for the myosin alkali light-chain isoforms MLC 1f/3f and MLC 1sb in adult human muscles, which are distributed in characteristic fibre type specific patterns. In situ hybridizations of 33P-labelled probes were compared with probes carrying 35S or digoxigenin labels. Signals of equal strength were obtained with each of the three labels. The preferentially peripheral localization of these mRNAs in the muscle fibres could be clearly seen with all three probes, with digoxigenin probes providing the best resolution. 33P can serve as a viable alternative in this type of experiment. These experiments with adult human muscles also showed that the post mortem stability of RNA in human muscle is better than generally assumed. We could detect no signs of degradation in RNA prepared from heart ventricle as well as skeletal muscle up to 24 hours post mortem. In situ hybridizations worked equally well in biopsy material as in post mortem samples.