Procathepsin and acid phosphatase are stored in Musca domestica yolk spheres

Yolk spheres present in mature invertebrate oocytes are composed of yolk pr oteins and proteolytic enzymes. In the fly Musca domestica, yolk proteins a re degraded during embryogenesis by a cathepsin-like proteinase: that is st ored as a zymogen. An acid phosphatase is also active in the yolk spheres d uring Musca embryogenesis. In this paper we show that procathepsin and acid phosphatase are initially stored by a different pathway from the one follo wed by yolk protein precursors. Both enzymes are taken up by the oocytes an d transitorily stored into small vesicles (lysosomes) surrounding the early yolk spheres. Fusion of both structures. the early yolk spheres and lysoso mes, creates the mature yolk spheres. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.