Current Biology
Volume 14, Issue 24, 29 December 2004, Pages 2252-2258
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C. elegans MOM-5/Frizzled Functions in MOM-2/Wnt-Independent Cell Polarity and Is Localized Asymmetrically prior to Cell Division

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Abstract

C. elegans embryonic cells have a common anterior/posterior (a/p) polarity that is apparent in the localization of the transcription factor POP-1 1, 2. The level of nuclear POP-1 remains high in the anterior daughters of dividing cells but is lowered in the posterior daughters 2, 3. To generate POP-1 asymmetry, most early embryonic cells require contact with signaling cells that express the ligand MOM-2/Wnt 4, 5; the point of cell contact specifies the daughter with low nuclear POP-1 6, 7. In contrast, slightly older embryonic cells that have no apparent prior exposure to Wnt signaling can generate POP-1 asymmetry, provided these cells express MOM-5/Frizzled [7]. We show here that MOM-5::GFP is enriched at the posterior pole of cells prior to division and that a similar asymmetry is observed in cultured cells with no apparent prior exposure to Wnt signaling. While depleting these latter cells of MOM-5/Frizzled causes both daughter cells to have high levels of POP-1 [7], we show that both daughter cells have low levels of POP-1 in embryos with atypically high levels of MOM-5::GFP. These results suggest that MOM-5/Frizzled asymmetry leads to POP-1 asymmetry. In later embryogenesis, we find that MOM-5::GFP localizes to the leading edges of epidermal cells during ventral enclosure. These localization patterns suggest a parallel between MOM-5/Frizzled and the roles of Drosophila Frizzled in planar polarity and dorsal enclosure.

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