PRIMARY STRUCTURE, DEVELOPMENTAL EXPRESSION, AND IMMUNOLOCALIZATION OF THE MURINE LAMININ ALPHA-4 CHAIN

The complete primary structure of the mouse laminin alpha 4 chain was derived from cDNA clones. The translation product contains a 24-residu e signal peptide preceding the mature alpha 4 chain of 1,792 residues. Northern analysis on whole mouse embryos revealed that the expression was weak at day 7, but it later increased and peaked at day 15. In ad ult tissues the strongest expression was observed in lung and cardiac and skeletal muscles. Weak expression was also seen in other adult tis sues such as brain, spleen, liver, kidney, and testis. By in situ hybr idization of fetal and newborn tissues, expression of the laminin alph a 4 chain was mainly localized to mesenchymal cells. Strong expression was seen in the villi and submucosa of the developing intestine, the mesenchymal stroma surrounding the branching lung epithelia, and the e xternal root sheath of vibrissae follicles, as well as in cardiac and skeletal muscle fibers. In the developing kidney, intense but transien t expression was associated with the differentiation of epithelial kid ney tubules from the nephrogenic mesenchyme. Immunohistologic staining with affinity-purified IgG localized the laminin alpha 4 chain primar ily to lung septa, heart, and skeletal muscle, capillaries, and perine urium.