Cell-substrate and cell-cell interactions differently regulate cytoskeletal and extracellular matrix protein gene expression.

In this study, cellular events during tissue formation were investigated at the mRNA level using the Northern blot technique. The levels of expression of mRNAs encoding specific proteins (beta-actin, fibronectin, and laminin) during tissue formation on tissue culture dishes were quantitatively assessed using a Northern blot technique with autoradiography. The level of beta-actin mRNA increased with incubation time and reached a maximal level near the confluent state, followed by reduced beta-actin mRNA expression at a later stage of tissue formation. The time course of beta-actin mRNA expression corresponded well to the time course of morphologic changes and cytoskeletal organization in adherent cells. Expression of the mRNAs encoding the extracellular matrix proteins fibronectin and laminin was initiated at the proliferation stage. After maximum expression levels of these two mRNAs were reached at the confluent stage, a gradual decrease in their expression levels was seen during long-term culture. Expression patterns of mRNAs encoding cytoskeletal and extracellular matrix proteins strongly depended on the type of artificial substrates used; a mRNA expression pattern similar to that observed during tissue formation on tissue culture dishes was observed on a cell-adhesive substrate during tissue formation, whereas reduced expression was seen during tissue formation on a less adhesive substrate. Thus, the dynamic changes occurring during tissue formation were quantified to investigate the roles of artificial substrates in tissue formation at the mRNA level.