Hatching through enzymatic breakdown of the embryonic coats in the lancelet, Branchiostoma lanceolatum (Cephalochordata)

A study was made of the hatching process of the lancelet, Branchiostoma lanceolatum (Amphioxus), under laboratory conditions. Embryos in the early neurula stage (5 to 6 pairs of somites) escape through a hole made in the fertilization envelope, following intensive rotatory movements and partial digestion of the envelope. Using the chromogenic substrate Hide Powder Azure (HPA) at pH 8.0, proteolytic activity was detected in the hatching medium. The effect of various protease inhibitors was investigated. Whereas the activity was only slightly affected by inhibitors of trypsin, chymotrypsin or thiol proteases, chelating agents such as EDTA and 1,10-phenanthroline prevented the degradation of HPA, as well as the breakdown of the vitelline membrane of alcohol fixed oocytes by the protease from hatching fluid. These data suggest the presence of a metalloprotease in the hatching medium. How far this enzyme can be compared with hatching enzymes found in echinoderms and fishes (where they have been identified as matrix degrading metalloproteases), awaits further study of the lancelet enzyme, including its isolation and purification.