Neuronal dendritic-axonal asymmetry, once established, is normally stabilized in order to maintain information flow. However, polarity changes can occur in response to developmental changes or in culture. The six C. elegans GABAergic DD motoneurons remodel their synaptic connectivity patterns as the worm matures from the L1 to the L2 stage. (1) In L1 worms these DD motoneurons form neuromuscular junctions (NMJs) to ventral muscles. In the L2 to adult stage the NMJs are reformed onto dorsal muscles without an alteration in the morphology of these motoneurons. A recent study in the mouse CNS has shown that cerebellar granule cells secrete factors that induce axon and growth cone remodeling in mossy fibers. (2) This effect is blocked by a Wnt antagonist and mimicked by Wnt7a which is expressed by granule cells. To investigate whether DD remodeling may employ Wnt signaling, we are examining the effect of various existing Wnt signaling mutants. We have used the Punc-25 driven SNB-1::GFP marker to visualize the presynaptic pattern of DD neurons. (3) Preliminary results reveal that four maternal effect Wnt signaling mutants,
mom-2,
mom-4,
lit-1 and
pop-1 do not have a dominant effect on DD remodeling. We are currently examining the zygotic effect of these mutants. The zygotic Wnt signaling mutants
egl-20 and
lin-17 do not have any effect on DD remodeling. In
egl-27 mutants however, DD motoneurons appear to form synapses to dorsal muscles in the L1 stage. We are further investigating whether this effect may be due to a cell fate alteration. (1) White JG, Albertson DG, Anness MAR Nature 271 , 764-766 (1978) (2) Hall AC, Lucas FR, Salinas PC Cell 100 , 525-535 (2000) (3) Hallam SJ and JinY Nature 395 , 78-82(1998)