HATCHING THROUGH ENZYMATIC BREAKDOWN OF T HE EMBRYONIC COATS IN THE LANCELET, BRANCHIOSTOMA-LANCEOLATUM (CEPHALOCHORDATA)

A study was made of the hatching process of the lancelet, Branchiostom a lanceolatum (Amphioxus), under laboratory conditions. Embryos in the early neurula stage (5 to 6 pairs of somites) escape through a hole m ade in the fertilization envelope, following intensive rotatory moveme nts and partial digestion of the envelope. Using the chromogenic subst rate Hide Powder Azure (HPA) at pH 8.0, proteolytic activity was detec ted in the hatching medium. The effect of various protease inhibitors was investigated. Whereas the activity was only slightly affected by i nhibitors of trypsin, chymotrypsin or thiol proteases, chelating agent s such as EDTA and 1,10-phenanthroline prevented the degradation of HP A, as well as the breakdown of the vitelline membrane of alcohol fixed oocytes by the protease from hatching fluid. These data suggest the p resence of a metalloprotease in the hatching medium. How far this enzy me can be compared with hatching enzymes found in echinoderms and fish es (where they have been identified as matrix degrading metalloproteas es), awaits further study of the lancelet enzyme, including its isolat ion and purification.