The transforming gene (v-mos) of Moloney murine sarcoma virus has been intensively studied in order to understand how it transforms mammalian cells. The characterization of oncogenes such as mos has also led to the identification of normal cellular genes that control cell growth, proliferation and development. Recently it was shown that the c-mos proto- oncogene is developmentally expressed in germ cells. In mouse and Xenopus oocytes, expression of mos is essential for meiosis and this function is likely to be conserved in humans. Thus, the overall objective of this grant is to extend our understanding of how mos regulates cell cycle control, both during oncogenic transformation as well as meiosis. Three specific areas of research are proposed. First, we will examine the role of mos(xe) in Xenopus laevis oocyte maturation. Evidence suggest that during oocyte maturation the mos protein plays a role in the activation or stabilization of MPF. Therefore, we will examine the potential effects of mos(xe) on the phosphorylation state of p34(cdc2). We will study the effect of cyclin phosphorylation on oocyte maturation and on the ability of mos(xe) to accelerate oocyte maturation induced by cyclin. Experiments are also proposed to further investigate the requirement for mos(xe) expression during progression from meiosis I to meiosis II. Additional experiments will determine the interaction between the mos(xe) protein and microtubules, and also the effects of mos(xe) expression on the activation of MAP kinase during oocyte maturation. Second, we will study the importance of phosphorylation for activation of mos(xe). Evidence suggests that the biological activities of the mos(xe) protein are regulated in part by phoshorylation. In this section, we propose to examine in detail the time course of phosphorylation with respect to the appearance of both maturation promoting factor (MPF) and cytostatic factor (CSF) during meiotic maturation. These studies will include the determination of major phosphorylation sites in the mos(xe) protein. In addition to potential sites of autophosphorylation, we will attempt to characterize other kinase(s) responsible for phosphorylating the mos(xe) protein. Third, we will examine the role of mos expression in mammalian cell transformation. We will undertake the construction of mammalian cell lines allowing rapid inducible expression of mos. Our goal will be to isolate cell lines which are inducible for either morphological transformation or cytotoxicity (which has been correlated with mos overexpression.) These studies will allow us to determine the threshhold level of mos expression required to achieve mammalian cell transformation or cytotoxicity. The effects of inducible mos overexpression on the mammalian cell cycle will be examined.
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