The major objective of this proposal is to understand the molecular mechanisms that control gene expression at the posttranscriptional level in early vertebrate development. In particular, Xenopus oocytes contain many dormant mRNAs that become translated when the cells re-enter the meiotic divisions (oocyte maturation). While dormant, the poly(A) tails on these mRNAs are short;translation ensues when the tails lengthen in response to hormonal stimulation. CPEB is a cytoplasmic polyadenylation element (CPE) specific RNA binding protein that controls poly(A) tail length;it does so in conjunction with several other proteins including CPSF, symplekin, Gld2 (a poly(A) polymerase), and PARN (a deadenylase). While CPE-containing pre-mRNAs acquire a typical long poly(A) tail in the nucleus, the tail is removed once the RNA is exported to the cytoplasm. There, CPEB, Gld2, PARN, and other factors associate with the RNA;Gld2 and PARN are both active, but because PARN is more active, the poly(A) tail is removed. Upon hormonal stimulation, a cascade of events leads to CPEB phosphorylation, an event that expels PARN from the ribonucleoprotein (RNP) complex and allows Gld2-catalyzed default poly(A) tail growth. Polyadenylation controls translation through Maskin, a CPEB binding protein. When the poly(A) tail is short, Maskin is also bound to eIF4E and translation is repressed;an elongated poly(A) tail induces Maskin dissociation from eIF4E, allowing translation to proceed. How the elongated poly(A) tail causes Maskin-eIF4E dissociation will be investigated particularly as it relates to the dynamic change in the factors associated with the CPEB-containing RNP complex during oocyte maturation. Recent experiments have shown that CPEB transiently resides in the nucleus where it interacts with CPE-containing pre-mRNA as well as several processing factors. We will determine whether CPEB is involved in nuclear RNA processing and whether its nuclear experience determines the cytoplasmic fate of mRNA. Finally, an upstream event that is necessary for CPEB-mediated polyadenylation is the translational activation of RINGO/Spy mRNA, which encodes an atypical cyclin B1-like protein. Pumilio is the key factor that controls RINGO/Spy translation, and the mechanism by which it does so will be determined. Translational control by CPEB is widespread in metazoans, and it not only mediates germ cell development, but neuronal synaptic plasticity, hippocampal-dependent memories, and cellular senescence as well. Thus, an understanding of the fundamental biochemical events controlled by CPEB has important implications for human health, particularly fertility, neurodegeneration, and perhaps longevity and cancer.This project will investigate the regulation of gene expression in early animal development. In particular, we will examine RNA processing and translational control. Because of the fundamental nature of this work, it has important implications for fertility, neurodegeneration, and cancer.
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