Targeted disruption of the LAMA3 gene in mice reveals abnormalities in survival and late stage differentiation of epithelial cells

Laminin 5 regulates anchorage and motility of epithelial cells through integrins alpha 6 beta 4 and alpha 3 beta 1 respectively. We used targeted disruption of the LAMA3 gene, which encodes the alpha 3 subunit of laminin 5 and other isoforms, to examine developmental functions that are regulated by adhesion to the basement membrane (BM). In homozygous null animals, profound epithelial abnormalities were detected that resulted in neonatal lethality, consistent with removal of all alpha 3-laminin isoforms from epithelial BMs Alterations in three different cellular functions were identified. First, using a novel tissue adhesion assay, we found that the mutant BM could not induce stable adhesion by integrin alpha 6 beta 4. consistent with the presence of junctional blisters and abnormal hemidesmosomes. In the absence of laminin 5 function, we were able to detect a new ligand for integrin alpha 3 beta 1 in the epidermal BM, suggesting that basal keratinocytes can utilize integrin alpha 3 beta 1 to interact with an alternative ligand. Second, we identified a survival defect in mutant epithelial cells that could be rescued by exogenous laminin 5, collagen, or an antibody against integrin alpha 6 beta 4, suggesting that signaling through beta 1 or beta 4 integrins is sufficient for survival. Third, we detected abnormalities in ameloblast differentiation in developing mutant incisors indicating that events downstream of adhesion are affected in mutant animals. These results indicate that laminin 5 has an important role in regulating tissue organization, gene expression, and survival of epithelium.