Integrin Expression in Developing Smooth Muscle Cells

We studied the specific expression patterns and distributions of α 1 and β 1 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 α 1 and β 1 integrins isolated from avian gizzards were used as probes. Gels and blots showed that the amount of α 1 and β 1 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-α 1 and anti-β 1 integrin was prominent at membrane-associated dense plaques (MADPs) and at filament anchoring regions at cell ends. This indicates that α 1 and β 1 integrin expression coincides temporally with the intracellular proliferation and reorientation of myofilaments. The similarity in distribution patterns of α 1 and β 1 integrins during development suggests that the two integrin subunits are synchronously expressed during development and do not appear sequentially.