Expression of the Nicotinic Receptor α7 Gene in Tendon and Periosteum During Early Development

Abstract

One of the most abundant nicotinic acetylcholine receptors expressed in the central and peripheral nervous systems is a species that contains the α7 gene product, binds α‐bungarotoxin with high affinity, and has a high relative permeability to calcium. The α7 gene is also expressed at low levels in embryonic muscle tissue. We show here that the α7 gene is expressed in tendon fibroblasts and periosteal cells during development. In situ hybridizations identify α7 transcripts in tissue sections containing embryonic tendon and periosteum. RNase protection experiments demonstrate α7 mRNA in primary tendon cells grown in culture. Immunofluorescence with subunit‐specific monoclonal antibodies reveals α7 protein in embryonic tendon. Immunoprecipitation assays with the antibodies indicate that the α7‐containing species in tendon is capable of binding α‐bungarotoxin and that a similar species can be identified at low levels on the surface of fibroblasts in culture. The results show that the α7 gene product is expressed in a range of tissues, including cells thought to be nonexcitable. The distribution of α7 expression early in development and the ability of α7‐containing receptors to elevate intracellular calcium suggest that the gene may influence a variety of calcium‐dependent events during embryogenesis.

An α7 nicotinic receptor-G protein pathway complex regulates neurite growth in neural cells*

“…It is noteworthy, that none of the drug treatment conditions appeared to significantly alter the percentage of cells with at least one process longer than the cell body (an inclusion criteria in the analysis) thus confirming that a7 receptor activity is associated with changes in neurite growth within differentiating cells. Our findings are consistent with earlier observations on the inhibitory effects of ACh on neurite development (Hieber et al, 1992;Lauder and Schambra, 1999) and suggest a role for a7 in structural and synaptic development (Corriveau et al, 1995;Romano et al, 1997). However, since nicotine and ACh activate other cholinergic receptors, the contribution of non-a7 receptors to neurite growth cannot be excluded.…”

Expression of non-neuronal cholinergic system in osteoblast-like cells and its involvement in osteogenesis

“…4, 5). The presence of subunit α7 has previously been reported for the periosteum, which contains pre-osteoblasts, mesenchymal cells, and fibroblasts (Romano et al 1997). The occurrence of the nAChR α7 subunit in fibroblasts is also known from other organs, e.g., skin and lung in which it mediates collagen expression (Arredondo et al 2003;Sekhon et al Fig.…”

“…The nicotine-induced increase in cell proliferation in human trabecular bone cores, as revealed by an increase in osteopontin protein amount analyzed by Western blot, is inhibited in a dosedependent manner by the addition of D-tubocurarine, an antagonist of nAChR (Walker et al 2001). The occurrence of nAChR subunits α4 and α7 has been demonstrated in bone and periosteum by using reverse transcription with the polymerase chain reaction (RT-PCR) and in situ hybridization, respectively (Walker et al 2001;Romano et al 1997). In this report, we have investigated the expression of the whole cholinergic system in human and mouse osteoblastlike cell cultures by utilizing RT-PCR.…”

Nicotinic receptor signaling in nonexcitable cells

“…In vertebrate muscle, transcripts for ␣4, ␣5, ␣7, and ␤4 have been detected, and their levels are regulated with embryonic age, suggesting a role for nAChRs during skeletal muscle development (Corriveau et al, 1995). The nAChR ␣7 gene is expressed in the chick tendon and periosteum during development (Romano et al, 1997). Neuronal stem cells and progenitors express functional nAChRs ( Komourian and Quik, 1996;Berger et al, 1998;Atluri et al, 2001).…”