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Epidermal growth factor (EGF) induces fibronectin (FN) and FN mRNA in rat liver epithelial cells, under conditions where the factor also induces the cells to migrate. Newly synthesized protein is secreted into the medium and deposited as substratum-bound extracellular matrix. The levels of mRNA and the amount of protein synthesized are not influenced by cyclic AMP or dexamethasone, factors that have been found to modulate FN expression in other cells. However, the cells are sensitive to the factors, suggesting a cell-specific regulation. The EGF-induced RNA contains the sequences EIIIA and EIIIB characteristic of cellular fibronectin.

Isolated seminiferous tubules of rat testis contain considerable urokinase-inhibiting activity. An immunohistological analysis revealed the presence of plasminogen activator inhibitor type 1 (PAI-1) in the basement membrane as well as in the interior of the tubules. Distribution and intensity of the intratubular immunoreactivity depends on the stage of the seminiferous cycle. A relatively weak signal is present around elongated nuclei of spermatids at the beginning of chromatin condensation. The signal intensity increases in the course of differentiation until a maximum is reached at stages VII-VIII. In these stages PAI-1 immunoreactivity is localised around the nuclei of the late spermatids as well as along their tails. Spermatozoa in the ductus epididymis also strongly react with the PAI-1-specific antiserum, suggesting that the inhibitor remains associated with the germ cells after spermiation and during maturation in the epididymis. In intact mature spermatozoa isolated from epididymis cauda by 'swimming-up' in non-capacitation medium, PAI-1 antigen is localised on the plasma membrane surrounding the head. In addition, in fixed and permeabilised cells the immunoreactivity is detectable in the acrosome and in the tail. Possible functions of PAI-1 in spermatogenesis, sperm motility and sperm-egg interaction are discussed.