The cell cycle can occur in starfish oocytes and embryos without the production of transferable MPF (maturation-promoting factor)

Abstract

All cells undergoing the transition from interphase to metaphase have been postulated to contain a "maturation-promoting factor" (MPF) capable of causing meiotic maturation when injected into immature oocytes. We have shown in an accompanying paper (A. Picard, M. C. Harricane, J. C. Labbe, and M. Doreé, 1988, Dev. Biol. 128, 121-128) that the basic oscillator driving the cell cycle still operates in maturing starfish oocytes and fertilized eggs in the absence of germinal vesicle (GV) material. Under such conditions of enucleation, we now show, however, that MPF activity cannot be detected after hormonal stimulation of prophase-arrested oocytes in Astropecten or after the normal time of second meiotic cleavage in Marthasterias. In contrast, cell cycles occur with the production of transferable MPF activity in embryos from which both pronuclei have been removed after fertilization. Reinjection of the entire contents of a GV after the normal time of second meiotic cleavage restores the ability of cytoplasm to induce meiotic maturation in immature recipient oocytes after transfer. Transduction of the hormonal stimulus at the level of the plasma membrane, stimulation of the phosphorylation of cytoplasmic proteins, and activation of a cycling Ca2+- and cyclic nucleotide-independent histone kinase still occur in the absence of GV material. Since previous studies have demonstrated that the presence of GV material in the recipient oocytes is absolutely required in starfish for the amplification of microinjected MPF (Kishimoto et al., 1981; Picard and Doree, 1984), we propose that some unidentified component of the GV is required, at least after the normal time of second meiotic cleavage in donor oocytes and at any time in recipient oocytes, for the successful transfer of MPF activity in starfish.