Wnt pathway components orient a mitotic spindle in the early Caenorhabditis elegans embryo without requiring gene transcription in the responding cell

Ann Schlesinger; Christopher A. Shelton; Julin N. Maloof; Marc Meneghini; Bruce Bowerman

Wnt pathway components orient a mitotic spindle in the early Caenorhabditis elegans embryo without requiring gene transcription in the responding cell

Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403 USA; Department of Biochemistry and Biophysics, University of California, San Francisco, California 94143 USA

Abstract

In a four-cell-stage Caenorhabditis elegans embryo, Wnt signaling polarizes an endoderm precursor called EMS. The polarization of this cell orients its mitotic spindle in addition to inducing endodermal fate in one daughter cell. Reducing the function of Wnt pathway genes, including a newly identifiedGSK-3β homolog called gsk-3, disrupts endoderm induction, whereas only a subset of these genes is required for proper EMS mitotic spindle orientation. Wnt pathway genes thought to act downstream of gsk-3 appear not to be required for spindle orientation, suggesting that gsk-3 represents a branch point in the control of endoderm induction and spindle orientation. Orientation of the mitotic spindle does not require gene transcription in EMS, suggesting that Wnt signaling may directly target the cytoskeleton in a responding cell.

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