CAMP-STIMULATED TERMINATION OF VITELLOGENESIS IN HYALOPHORA-CECROPIA - FORMATION OF A DIFFUSION BARRIER AND THE LOSS OF PATENCY

Activation of cAMP-dependent protein kinase (PKA) by cell-permeable an alogs of cAMP causes early and mid-vitellogenic follicles of Hyalophor a cecropia to terminate vitellogenin uptake [Wang and Telfer, 1994, In sect Biochem. Mol. Biol. 26, 85-94 (1996)]. The response is shown here to entail the formation of an epithelial diffusion barrier, Follicle cells that have been loosely organized to provide intercellular pathwa ys for the movement of vitellogenin to the oocyte surface transform ir ate a tight epithelium within 1-2 h of exposure to PKA activators, The follicle cells can now prevent the escape of Lucifer yellow CH that h as been iontophoresed into the space surrounding the oocyte, and the e ntry of labeled vitellogenin from the medium, As they form this. funct ional equivalent of a tight junction, the follicle cells further reduc e the intercellular spaces by enlarging and pressing against each othe r, and by slowing the secretion of the sulfated glycosaminoglycan matr ix that separates them during vitellogenesis, The activation of PKA in early and mid-vitellogenic follicles thus appears to trigger prematur ely a set of changes that do not normally occur until the follicle has grown to a length of about 2.0 mm. (C) 1997 Elsevier Science Ltd.