TRANSCRIPTS FOR THE ACETYLCHOLINE-RECEPTOR AND ACETYLCHOLINE ESTERASE SHOW DISTRIBUTION DIFFERENCES IN CULTURED CHICK MUSCLE-CELLS

In situ hybridization of chick cultured muscle cells using exonic DNA probes for both AChR alpha-subunit and the catalytic subunit of AChE, revealed major differences in the distribution of label both over nuclei and in their surrounding cytoplasm, although some overlap in these distributions exists. For the AChR alpha-subunit there is a highly skewed distribution of labeled nuclei, with 35 % of the nuclei being relatively inactive (<0.25 times the mean label) and approximately 10% being very heavily labeled (>2.5 times the mean label). In contrast the nuclei labeled with the exonic probe for the AChE transcripts had a more Gaussian distribution, yet with some slight skewness in the direction of a few heavily labeled nuclei. There was also a difference in the cytoplasmic distribution of the label. The AChR alpha-subunit mRNA was mainly within 4-mu-m of labeled nuclei while the AChE mRNA was more widely distributed throughout the cytoplasm, possibly within a 10-mu-m rim around labeled nuclei. An intronic probe for the AChE gave the identical distribution of nuclear label to that of the exonic probe (but without any cytoplasmic label). In addition, calibration of the technique indicated that per myotube the AChE transcript is about sixfold more abundant than the AChR a-subunit transcript.