Expression of the nicotinic receptor alpha 7 gene in tendon and periosteum during early development.

One of the most abundant nicotinic acetylcholine receptors expressed in the central and peripheral nervous systems is a species that contains the alpha 7 gene product, binds alpha-bungarotoxin with high affinity, and has a high relative permeability to calcium. The alpha 7 gene is also expressed at low levels in embryonic muscle tissue. We show here that the alpha 7 gene is expressed in tendon fibroblasts and periosteal cells during development. In situ hybridizations identify alpha 7 transcripts in tissue sections containing embryonic tendon and periosteum. RNase protection experiments demonstrate alpha 7 mRNA in primary tendon cells grown in culture. Immunofluorescence with subunit-specific monoclonal antibodies reveals alpha 7 protein in embryonic tendon. Immunoprecipitation assays with the antibodies indicate that the alpha 7-containing species in tendon is capable of binding alpha-bungarotoxin and that a similar species can be identified at low levels on the surface of fibroblasts in culture. The results show that the alpha 7 gene product is expressed in a range of tissues, including cells thought to be nonexcitable. The distribution of alpha 7 expression early in development and the ability of alpha 7-containing receptors to elevate intracellular calcium suggest that the gene may influence a variety of calcium-dependent events during embryogenesis.