POTENTIAL ROLE IN DEVELOPMENT OF THE MAJOR CYSTEINE PROTEASE IN LARVAE OF THE BRINE SHRIMP ARTEMIA-FRANCISCANA

Encysted embryos and larvae of the brine shrimp Artemia franciscana co ntain a cysteine protease which represents over 90% of the protease ac tivity in these organisms. We have used immunocytochemical methods to determine the localization and potential role of the cysteine protease in development of young larvae. In prenauplius larvae, there is inten se staining for the protease on the basal side of the epidermal layer in the posterior region and diffuse staining for the protease througho ut the embryo. In first instar larvae, cysteine-protease staining beco mes intense in the midgut-forming area where a reticulum-like pattern emerges in cells with an abundance of yolk platelets. Cysteine-proteas e staining in second instar larvae becomes intense in the apical side of epidermal cells and in the basal and apical zones of midgut cells. Subcellular localization of the protease in the epidermis and midgut o f young larvae using immunogold electron microscopy suggests that most is located in the cytosol and extracellular matrix adjacent to these cells. Addition of cysteine-protease inhibitors to the growth medium, especially the fluoromethyl ketone Z-Phe-Ala-CH2F, inhibits growth and segmentation of the thorax. Collectively, these observations suggest that the major cysteine protease in embryos and larvae functions in yo lk utilization, as a hatching enzyme, in apolysis during the molt cycl e, and as a digestive enzyme when the swimming larvae begin to feed.