Amphibian embryo protease inhibitor. III. Binding studies on the trypsin inhibitor and properties of its yolk-bound form

Induction and inhibition of amphibian (Rana pipiens) oocyte maturation by protease inhibitor (TPCK)

We report for the first time that oocyte nuclear and cytoplasmic maturation are triggered in vitro in non-hormone-treated amphibian (Rana pipiens) ovarian follicles following transient exposure to synthetic chymotrypsin inhibitor N alpha-tosyl-L-phenylalanine-chloromethyl ketone (TPCK). The mechanism of action of TPCK in regulating oocyte maturation was investigated and compared to that induced by progesterone or pituitary hormone. Follicular oocytes failed to mature following continuous exposure to the same doses of TPCK in the presence or absence of progesterone. Continuous treatment of follicles with lower levels of TPCK occasionally induced GVBD in the absence of progesterone and augmented maturational effects of low levels of progesterone. TPCK induced maturation of intrafollicular oocytes without stimulating progesterone production and also induced maturation of naked oocytes. Stimulation of follicular progesterone synthesis following gonadotropin stimulation or addition of pregnenolone was inhibited by TPCK, indicating that TPCK affects metabolic processes in both the somatic and germinal components of the ovarian follicle. Oocyte maturation induced by either TPCK or progesterone was inhibited by cycloheximide, calcium-deficient medium, and forskolin. Results suggest that TPCK induces oocyte maturation independent of steroidogenesis via mechanisms similar to those triggered by progesterone involving protein synthesis, formation of cytoplasmic maturation-promoting factor (MPF), and changes in cAMP levels. Our data indicate that a chymotrypsin-like protease plays a role(s) in regulating the oocyte meiotic maturation process.

Ultrastructural indications for autosynthetic proteinaceous yolk formation in amphibian oocytes

The formation of proteinaceous yolk is a main feature during amphibian oogenesis. The main bulk is built up by a process called heterosynthesis. The precursor complex vitellogenin is synthesized in the liver, transported by the bloodstream to the ovary, where the oocytes sequester the material by means of endocytosis. This pathway has been described in detail by many authors. The ultrastructural study of amphibian oocytes indicates on the other hand a small but distinct contribution of the oocyte itself towards yolk formation. This process has been called autosynthesis and starts before the onset of heterosynthetic activities. The cell organelles possibly involved in yolk-recursor and yolk-platelet formation are the nuclear envelope, annulate lamellae, endoplasmic reticulum, Golgi complex, GERL and mitochondria. The aim of this paper is to discuss the data, mainly of ultrastructural nature, so far accumulated during the study of autosynthesis. It is hoped to stimulate more biochemically orientated research in this field.

Amphibian embryo protease inhibitor. V. Effect of calcium on the distribution of amphibian trypsin inhibitor during fertilization and subsequent development of Rana pipiens

In previous publications we have documented the existence in oocytes and embryos of a variety of forms (notably Rana pipiens), massive amounts of a powerful inhibitor of trypsin-like enzymes (ATI). The bulk of the inhibitor in Rana pipiens is localized in yolk platelets. We present evidence here that the distribution of the inhibitor between yolk platelets and cytosol changes and that this change is mediated by variations in the distribution of calcium ions. There is an inverse relationship between ATI and free calcium in the cytosol. Several workers have demonstrated a dramatic rise in free cytosol calcium immediately following fertilization. We confirm this observation, and demonstrate that there is a parallel and equally dramatic decrease in free cytosol ATI during this period. Experiments with purified yolk platelets indicate that calcium effects a release of sequestered inhibitor from these particles. Other experiments indicate that calcium mediates ATI-lippovitellin associations. A calcium mediated flux of ATI from cytosol to yolk is proposed as a device for controlling limited proteolysis in the cytoplasm. We offer this as a model for studying the unmasking of mRNA which follows fertilization.

Amphibian embryo protease inhibitors. IV. Studies on an inhibitor of chymotrypsin and papain

Amphibian embryo chymotrypsin and papain inhibitor (ACPI) purified by the procedure described in this paper produces a single band on sodium dodecyl sulfate (SDS) gel electrophoresis and a single peak on Sephadex G-75 chromatography. Except for its enzyme specificity, ACPI is very similar to amphibian embryo trypsin inhibitor (ATI). Its molecular weight is about 10,500 and its amino acid composition is typical of many naturally occurring protease inhibitors. Inhibition develops slowly, is retarded by the presence of substrate and is temporary. ACPI is localized in the yolk platelets and its disappearance both from whole embryos and from select tissue types corresponds closely with that of ATI. Possible roles for amphibian embryo proteases and protease inhibitors in development are discussed.