Park Frederick D, Tenlen Jennifer R, Priess James R
Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA.
Curr Biol. 2004 Dec 29;14(24):2252-8. doi: 10.1016/j.cub.2004.12.019.
C. elegans embryonic cells have a common anterior/posterior (a/p) polarity that is apparent in the localization of the transcription factor POP-1. The level of nuclear POP-1 remains high in the anterior daughters of dividing cells but is lowered in the posterior daughters. To generate POP-1 asymmetry, most early embryonic cells require contact with signaling cells that express the ligand MOM-2/Wnt; the point of cell contact specifies the daughter with low nuclear POP-1. 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. 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, 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.
秀丽隐杆线虫胚胎细胞具有共同的前后极性，这在转录因子POP-1的定位中很明显。在分裂细胞的前子代中，核内POP-1水平仍然很高，但在后子代中则降低。为了产生POP-1的不对称性，大多数早期胚胎细胞需要与表达配体MOM-2/Wnt的信号细胞接触；细胞接触点决定了核内POP-1水平低的子代细胞。相比之下，那些没有明显预先接触Wnt信号的稍大胚胎细胞，如果这些细胞表达MOM-5/卷曲蛋白，也可以产生POP-1的不对称性。我们在此表明，MOM-5::GFP在细胞分裂前富集于细胞的后极，并且在没有明显预先接触Wnt信号的培养细胞中也观察到类似的不对称性。虽然去除这些细胞中的MOM-5/卷曲蛋白会导致两个子代细胞都具有高水平的POP-1，但我们表明，在MOM-5::GFP水平异常高的胚胎中，两个子代细胞都具有低水平的POP-1。这些结果表明，MOM-5/卷曲蛋白的不对称性导致了POP-1的不对称性。在胚胎发育后期，我们发现MOM-5::GFP在腹侧包被过程中定位于表皮细胞的前缘。这些定位模式表明MOM-5/卷曲蛋白与果蝇卷曲蛋白在平面极性和背侧包被中的作用之间存在平行关系。
