Rafael A. Fissore
Professor and Head, Department of Veterinary and Animal Sciences, University of Massachusetts
Ph.D.: University of Massachusetts Postdoctoral Training: Harvard Medical School
The sperm during fertilization initiates in mammalian oocytes a series of [Ca2+]i oscillations that are critical for activation and initiation of development. Two hypotheses have been suggested to explain the signaling mechanism(s) utilized by the sperm to trigger Ca2+ release, the receptor hypothesis and the fusion hypothesis. The fusion hypothesis predicts that a sperm cytosolic protein is released into the oocyte upon fusion. In accordance with this theory, extracts from sperm induce, when injected into oocytes, [Ca2+]i oscillations similar to those observed during fertilization. Our extracts, from porcine sperm, have the ability to induce high frequency Ca2+ release in mouse oocytes. Partial characterization of the active fraction revealed a pI of 6.7-7.0, a relative molecular weight of 29-68 kDa, and absence of gpi/oscillin, a protein previously thought to represent the active component of mammalian sperm. Future studies will establish the molecular nature of the active compound(s) and its possible site of action in mammalian eggs. In another project, we are characterizing the role of mos and MAP kinase in the initiation, and progression, of meiosis in mammalian oocytes. We are also interested in investigating the role of Ca2+ in the activation of maturation promoting factor (MPF) in the same stage of meiosis. For these experiments, mRNA’s coding for different proteins are injected into oocytes and the effects on kinase activity and meiosis progression is assessed by in vitro kinase assays and by Hoescht staining. Ca2+ activity is assessed by microfluorometry. Other general molecular and cellular biology techniques are used in the laboratory.