Distinct α 7A β 1 and α 7B β 1 integrin expression patterns during mouse development: α 7A is restricted to skeletal muscle but α 7B is expressed in striated muscle, vasculature, and nervous system

The laminin binding α 7 β 1 integrin has been described as a major integrin in skeletal muscle. The RNA coding for the cytoplasmic domain of α 7 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 α 7 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 α 7 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 immunohistochemistry revealed a postnatal induction of α 7B in the myocardium. In addition to striated muscle, α 7B integrin was localized to previously unreported nonmuscle locations such as a subset of vascular endothelia and restricted sites in the nervous system. Comparison of the α 7 integrin expression pattern with that of different laminin isoforms and dystroglycan revealed a coordinated temporal expression of dystroglycan, α 7 integrin, and laminin‐α2, but not laminin‐α1, in the forming skeletal muscle. We conclude that the α 7A and α 7B integrin variants are expressed in a developmentally regulated, tissue‐specific pattern suggesting different functions for the two splice forms. © 1996 Wiley‐Liss, Inc.