Studies proposed in this research project are concerned with the mechanisms by which processes of oocyte differentiation (growth, maturation and activation) are controlled. Ions, hormones and secondary cytoplasmic factors produced in response to hormones appear to mediate many of these changes. We have recently identified, in progesterone treated amphibian oocytes, a biologically active cytoplasmic material which inhibits transport of the yolk protein precursor (3H-vitellogenin) across the oocyte cell membrane when injected into non-hormone treated oocytes. Particularly, we wish to: (1) isolate and characterize this inhibitory factor, (2) establish whether it is the same of different from other biologically active cytoplasmic factors also present in hormone treated oocytes, (3) elucidate how the inhibitor is formed in the oocyte and how it acts on the cell membrane. In addition, we wish to determine if oocytes of other species in which the same stages of meiotic differentiation are controlled by different hormones or factors, contain similar biologically active cytoplasmic factors as those found in amphibian oocytes. The involvement of calcium ions in the process of differentiation will also be studied. Oocytes at different stages of in vitro differentiation will be analyzed to determine if there are (1) quantitative changes in the amount of bound and unbound calcium in the oocyte as determined by atomic absorption spectrophotometry, (2) alterations in calcium 45 incorporation, (3) changes in the binding capacity of oocytes microinjected with Ca45. The relative importance of different portions of the oocyte surface in the incorporation of vitellogenin and calcium, and in propagating the response to activating stimuli, will be examined.