Figure 5. The Wnt/b-Catenin Pathway Is Involved in the Asymmetric Division of the SMDD/AIY Mother (A) A general diagram of the Wnt/b-catenin asymmetry pathway. Only the components used in this study are presented; for a more complete description of the pathway, see Mizumoto and Sawa (2007). Upon stimulation of a Wnt receptor Frizzled, the kinases MOM-4/TAK-1 and LIT-1/NLK are activated in the posterior daughter cell. LIT-1 enters the nucleus and phosphorylates POP-1/TCF, promoting its nuclear export. As a consequence, POP-1 concentration is low in the posterior nucleus, allowing most of the POP-1 proteins to be associated with the limiting coactivator SYS-1/b-catenin, activating transcription, while in the anterior nucleus, POP-1 concentration is high; most of the POP-1 proteins are not associated with SYS-1 and therefore repress transcription. (B) Localization of POP-1::GFP (qIs74) or SYS-1::VENUS (qIs95) fusion proteins just after cleavage of the SMDD/ AIY mother (epidermal enclosure, ventral view, anterior to the left, SMDD/AIY lineage marked by
ttx-3promB::mcherry, otIs181 or otEx2644). (C) Expression of
ttx-3 (
ttx-3promB::gfp, mgIs18) in wild-type or
mom-4(
ne1539);
lit-1(
t1512) temperature-sensitive mutants. Embryos were shifted to the restrictive temperature just before cleavage of the SMDD/AIY mother and analyzed at the 1.5-fold stage or at hatching (lateral view, anterior to the left). The results are summed up at the bottom (red,
ttx-3 expression; numbers = number of animals showing expression in the cell depicted/total number of animals). (D) Expression of
ceh-10 (
ceh-10promA::gfp, lqIs4) in wildtype or
mom-4(
ne1539);
lit-1(
t1512) temperature-sensitive mutants. Embryos were shifted to the restrictive temperature just before cleavage of the SMDD/AIY mother and analyzed at the 1.5-fold stage (lateral view, anterior to the left). The results are summed up at the bottom (blue,
ceh-10 expression; numbers = number of embryos showing expression in the cell depicted/total number of embryos). Scale bar for all panels = 2 mm.