Originally published as Genetics Published Articles Ahead of Print on February 16, 2009.

Genetics, Vol. 181, 1249-1260, April 2009, Copyright © 2009
doi:10.1534/genetics.108.099440

FBF and Its Dual Control of gld-1 Expression in the Caenorhabditis elegans Germline

Nayoung Suh^*, Sarah L. Crittenden^,1, Aaron Goldstrohm^*,1,2, Brad Hook^*, Beth Thompson, Marvin Wickens^*, and Judith Kimble^*,,,3

^* Department of Biochemistry, Howard Hughes Medical Institute and Program in Cellular and Molecular Biology, University of Wisconsin, Madison, Wisconsin 53706

³ Corresponding author: Howard Hughes Medical Institute and Department of Biochemistry, University of Wisconsin, 433 Babcock Dr., Madison, WI 53706-1544.
E-mail: jekimble{at}wisc.edu

FBF, a PUF RNA-binding protein, is a key regulator of the mitosis/meiosis decision in the Caenorhabditis elegans germline. Genetically, FBF has a dual role in this decision: it maintains germ cells in mitosis, but it also facilitates entry into meiosis. In this article, we explore the molecular basis of that dual role. Previous work showed that FBF downregulates gld-1 expression to promote mitosis and that the GLD-2 poly(A) polymerase upregulates gld-1 expression to reinforce the decision to enter meiosis. Here we ask whether FBF can act as both a negative regulator and a positive regulator of gld-1 expression and also investigate its molecular mechanisms of control. We first show that FBF co-immunoprecipitates with gld-1 mRNA, a result that complements previous evidence that FBF directly controls gld-1 mRNA. Then we show that FBF represses gld-1 expression, that FBF physically interacts with the CCF-1/Pop2p deadenylase and can stimulate deadenylation in vitro, and that CCF-1 is partially responsible for maintaining low GLD-1 in the mitotic region. Finally, we show that FBF can elevate gld-1 expression, that FBF physically interacts with the GLD-2 poly(A) polymerase, and that FBF can enhance GLD-2 poly(A) polymerase activity in vitro. We propose that FBF can affect polyadenylation either negatively by its CCF-1 interaction or positively by its GLD-2 interaction.

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