Regulation of the β2 subunit chain of laminin in developing rabbit fetal lung tissue

Abstract

Laminins are a family of basement membrane-associated heterotrimeric proteins that are important in mediating the growth, migration, and differentiation of a variety of cell types. The β2 subunit chain is a component of several laminin isoforms, e.g., laminin-3, laminin-4, laminin-7, and possibly other, as yet uncharacterized laminin isoforms. Utilizing monoclonal antibodies directed against the β2 subunit chain of laminin, we detected this protein in fetal, neonatal, and adult lung tissues. The relative amount of laminin β2 subunit chain in fetal lung tissue increased as gestation proceeded, reaching its peak around the time of alveolar type II cell differentiation in the rabbit. The laminin β2 subunit chain was localized in early gestational age rabbit fetal lung tissue primarily in basement membranes of prealveolar ducts, airways, and smooth muscle cells of airways and arterial blood vessels. A rabbit laminin β2 cDNA was generated using RT-PCR and utilized as a probe in northern blot analysis to characterize the levels of laminin β2 mRNA in developing rabbit lung tissue. Similar to the pattern of laminin β2 protein induction observed in fetal lung tissue, laminin β2 mRNA levels were maximal late in gestation. Utilizing a laminin β2 chain cRNA probe and in situ hybridization, we detected laminin β2 mRNA in the epithelial cells of prealveolar ducts, the alveolar wall, and airways, as well as in connective tissue cells, and the smooth muscle cells of airways and blood vessels in fetal and adult lung tissues. In addition, using an in vitro explant model, we determined that alveolar type II cells are capable of synthesizing laminin β2 subunit mRNA and depositing this laminin subunit chain in the basement membrane beneath type II cells. The results of this study are suggestive that the laminin β2 chain may be involved in alveolar epithelial cell differentiation.