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Vol. 18, Issue 6, 2254-2263, June 2007

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Direct Observation of Regulated Ribonucleoprotein Transport Across the Nurse Cell/Oocyte Boundary

Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455

Submitted October 27, 2006; Revised March 19, 2007; Accepted March 30, 2007
Monitoring Editor: Susan Wente

In Drosophila, the asymmetric localization of specific mRNAs to discrete regions within the developing oocyte determines the embryonic axes. The microtubule motors dynein and kinesin are required for the proper localization of the determinant ribonucleoprotein (RNP) complexes, but the mechanisms that account for RNP transport to and within the oocyte are not well understood. In this work, we focus on the transport of RNA complexes containing bicoid (bcd), an anterior determinant. We show in live egg chambers that, within the nurse cell compartment, dynein actively transports green fluorescent protein-tagged Exuperantia, a cofactor required for bcd RNP localization. Surprisingly, the loss of kinesin I activity elevates RNP motility in nurse cells, whereas disruption of dynein activity inhibits RNP transport. Once RNPs are transferred through the ring canal to the oocyte, they no longer display rapid, linear movements, but they are distributed by cytoplasmic streaming and gradually disassemble. By contrast, bcd mRNA injected into oocytes assembles de novo into RNP particles that exhibit rapid, dynein-dependent transport. We speculate that after delivery to the oocyte, RNP complexes may disassemble and be remodeled with appropriate accessory factors to ensure proper localization.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

Address correspondence to: Thomas S. Hays (haysx001{at}umn.edu)

Abbreviations used: bcd, bicoid; Dhc, dynein heavy chain; Exu, Exuperantia; Gl, Glued; Gl, truncated Glued; Khc, kinesin I heavy chain; RNP, ribonucleoprotein.