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The laminin binding α₇β₁ integrin has been described as a major integrin in skeletal muscle. The RNA coding for the cytoplasmic domain of α₇ integrin undergoes alternative splicing to generate two major forms, denoted α_7A and α_7B. In the current paper, we have examined the developmental expression patterns of the α_7A and α_7B splice variants in the mouse. The α₇ integrin expression is compared to that of the nonintegrin laminin receptor dystroglycan and to that of laminin‐α1 and laminin‐α2 chains. α_7A integrin was found by in situ hybridization to be specific to skeletal muscle. Antibodies specific for α_7B integrin and in situ hybridization revealed the presence of α₇ mRNA and α_7B protein in the E10 myotome and later in primary and secondary myotubes. In the heart, α_7B integrin was not detectable in the endocardium or myocardium during embryonic and fetal heart development. Northern blot analysis and …