EXPRESSION OF TYPE-IV COLLAGEN-DEGRADING ACTIVITY DURING EARLY EMBRYONAL DEVELOPMENT IN THE SEA-URCHIN AND THE ARRESTING EFFECTS OF COLLAGEN-SYNTHESIS INHIBITORS ON EMBRYOGENESIS

Type IV collagen-degrading activity was expressed in homogenates of Ly techinus pictus embryos during embryogenesis. Activity was concentrate d 1,600-fold by ammonium sulfate fractionation, ion exchange, and gel chromatography and could not be activated further upon trypsin or orga nomercurial treatment. This enzyme activity could also degrade gelatin but had no affinity for type I, III, and V collagens. Activity was in hibited by addition of excess type IV collagen or gelatin, but was una ffected by addition of excess amounts of non-collagenous proteins of t he extracellular matrix. Chelators such as 1,10-phenanthroline or Na2E DTA reduced activity to control levels. Inhibitors of plasmin and of s erine and thiol proteases were without effect. Type IV collagen-degrad ing activity first became apparent at the stage of early mesenchyme bl astula. It then increased by a small increment and remained stable up to the stage of late mesenchyme blastula, coinciding with first detect ion of collagen synthesis and the appearance of the archenteron. There after, a sharp increase in activity was observed, concurrently with re modelling of the archenteron. Maximum activity was attained at prism s tage and was retained throughout to pluteus-larva stage. The specific inhibitors of collagen biosynthesis 8,9-dihydroxy-7-methyl-benzo[b]qui nolizinium bromide and tricyclodecane-9-yl xanthate arrested sea urchi n embryo development at early blastula, prevented the invagination of the archenteron, and reverted the expression of type IV collagen-degra ding activity to non-detectable levels. Removal of the inhibitors allo wed embryos to gastrulate and express type IV collagen-degrading activ ity.