Integrin expression in developing smooth muscle cells.

We studied the specific expression patterns and distributions of alpha1 and beta1 integrin subunits, the major cell adhesion receptors in smooth muscle, in developing smooth muscle cells from 16-, 18-, and 20-day embryonic gizzards and from 1- and 7-day post hatch chick gizzards by SDS-PAGE, immunoblotting, and immunoelectron microscopy. Antibodies raised against alpha1 and beta1 integrins isolated from avian gizzards were used as probes. Gels and blots showed that the amount of alpha1 and beta1 integrins increased as age increased, with major increases at 1 and 7 days post hatch. Image analysis of immunoelectron micrographs demonstrated that statistically significant labeling increases occurred between embryonic Days 16 and 18, between embryonic Day 20 and 1 day post hatch, and between 1 day and 7 days post hatch. Immunolabeling with both anti-alpha1 and anti-beta1 integrin was prominent at membrane-associated dense plaques (MADPs) and at filament anchoring regions at cell ends. This indicates that alpha1 and beta1 integrin expression coincides temporally with the intracellular proliferation and reorientation of myofilaments. The similarity in distribution patterns of alpha1 and beta1 integrins during development suggests that the two integrin subunits are synchronously expressed during development and do not appear sequentially. (J Histochem Cytochem 46:119-125, 1998)