Worm Breeder's Gazette 17(1): 37 (October 1, 2001)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Overexpression of UNC-40 in the touch neurons results in misdirection of the ALM axon.

Naomi Levy-Strumpf, Joseph G. Culotti

S.L. Research Institute of Mt. Sinai Hospital, 600 University Ave., Toronto M5G 1X5 Canada

Ectopic expression of UNC-5 in the touch neurons leads to reorientation of their axons toward the dorsal side in an unc-6 dependent manner (1). Therefore, the expression of UNC-5 changes their responsiveness to the UNC-6 signal from attraction to repulsion in the case of the AVM and PVM, and from non-responsiveness to repulsion in the case of the ALM. The latter suggests that the ALM contains the necessary machinery to respond to the UNC-6 signal, but is refractory to UNC-6 and sends a process longitudinally rather than ventrally. Several reasons might account for this, including that UNC-40, which is expressed in the ALM, is tightly regulated and therefore is prevented from responding to the UNC-6 ventral signal or that the forces that drive the ALM process longitudinally are dominant over the UNC-6 ventral cue. We have overexpressed an UNC-40gfp fusion protein in the touch neurons by using the mec-7 promoter. The overexpression of UNC-40 in the ALM results in a variety of axon reorientations which we intend to pursue further. The most common phenotype we observe is that the ALM process, which normally migrates longitudinally, reorients itself towards the ventral cord before it reaches the nerve ring, suggesting that it became responsive to the proximal UNC-6 signal expressed by the axon tracts entering the nerve ring. This finding suggests that the overexpression of UNC-40 in the ALM increases its sensitivity to UNC-6 and prompted us to initiate a screen to look for mutants in which the ALM sends a process ventrally at an earlier stage. Such further increase in the sensitivity to UNC-6 may result from mutations in genes that function either in the regulation of UNC-40 or in the opposing forces that prevent the ALM from sending its process ventrally .

1. Expression of the UNC-5 guidance receptor in the touch neurons of C. elegans steers their axons dorsally. Hamelin et al. Nature 364: 327-330 (1993).