Development Expression of the Genes Encoding the Four Subunits of the Chicken Muscle Acetylcholine Receptor

Subunit-specific DNA probes for the chicken muscle acetylcholine receptor have been used in conjunction with Northern blots and dot-blots based upon the SP6/T7 RNA polymerase reaction to quantitate changes in the steady-state mRNA levels of all four subunits during development. In pectoral muscle, maximal subunit transcript levels are observed at day 12 in ovo for α, days 12–16 in ovo for β, day 14 in ovo for γ, and days 12–14 in ovo for δ. Interestingly, two δ-subunit transcripts which have somewhat different patterns of temporal expression are detected. At the peak of expression of each subunit mRNA the absolute levels of the α-, β-, and γ-subunit transcripts are very similar (49.2, 66.0, and 70.7 attomoles of transcript/μg of poly(A)+ RNA, respectively) whereas that for the summed δ-subunit transcripts is significantly lower (17.8 attomoles/μg of poly(A)+ RNA). Further, this lower level of (δ-subunit mRNA is observed from day 10 to day 16 of embryonic development. We conclude that subunit transcript availability is important in the synthesis of acetylcholine receptor protein during development and that the level of the δ-subunit transcript can be rate limiting in the expression of this receptor.