Expression patterns of laminin α1 and α5 in human lung during development

Laminins are trimeric glycoprotein components of basement membranes. Each laminin has three structurally similar chains, designated α, β, and γ. Five laminin α chains are now known. In previous studies using monoclonal antibody 4C7, laminin α1 was thought to be present in basement membranes of human lung throughout development and in the adult, but recent expression studies have demonstrated that 4C7 identifies laminin α5 rather than α1. To determine the temporal and spatial patterns of laminin α1 and laminin α5 in developing human lung, we prepared complementary DNA probes specific for laminin α1 and α5 messenger RNAs (mRNAs). By Northern analysis, laminin α1 mRNA was prominent in first-trimester fetal lung, but was not detectable at 23 wk or at later times. In contrast, laminin α5 mRNA was readily detected in early fetal lung and remained present thereafter. Immunohistochemical staining demonstrated laminin α1 only in early fetal lung, whereas laminin α5 was persistent from the early fetal period. In situ hybridization localized laminin α1 expression to distal epithelium in the first-trimester lung, and laminin α5 to all epithelium and developing pulmonary arteries from the first trimester through the perinatal period. These studies indicate that laminin α1 expression is restricted to early human lung morphogenesis, whereas the expression of laminin α5 in human lung is continuous from early lung development through adult life. It is evident that laminin α1 and laminin α5 have different roles in the development of the human lung.