Worm Breeder's Gazette 13(3): 82 (June 1, 1994)

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.

Suppressors of unc-5 -inducedreorientation of the touch receptor axons.

Antonio Colavita[1], Joe Culotti[2]

[1]Samuel Lunenfeld Research Institute of Mt. Sinai Hospital
[2]Samuel Lunenfeld Research Institute of Mt. Sinai Hospital
Toronto, Canada

unc-5 encodes a transmembrane receptor ( UNC-5 )required for dorsally oriented pioneer growth cone migrations (Leung-Hagesteijn et al., Cell 71:289-299,1992). Ectopic expression of unc-5 in the touch receptor neurons under the control of the mec-7 promoter is sufficient to reorient their axons from longitudinal (ALMs, PLMs) or ventral (AVM, PVM) to a dorsal trajectory. This unc-5 induced reorientation is suppressed by unc-6 mutations (Hamelin et al., Nature 364:327-330, 1993)

These observations form the basis of a screen to identify additional mutations that, like unc-6 mutations, suppress unc-5 induced reorientation of the touch cell axons. To make this screen more efficient, we have constructed a dpy-20 rescued (nonRol) transgenic line that expresses unc-5 and lacZ in the touch neurons under the control of the mec-7 promoter. We mutagenized this line and did a visible screen for suppressors. From approximately 25,000 F2 animals examined, we recovered 18 mutations that identify six to eight genes. Among these are alleles of unc-6 , unc-40 ,and unc-44 .At present, we are genetically characterizing the other mutations and continuing the screen.

Suppression of 'ectopic unc-5 -induced'reorientation of the touch cell axons is more sensitive to the dose of unc-6 than is normal unc-5 mediated guidance. This is based on the observation that unc-6 ( ev400 )acts as a dominant suppressor of ectopic unc-5 -inducedguidance, but is recessive for motor neuron guidance. This observation provides some hope that an F1 suppressor screen similar to the F2 screen described above, might reveal mutations in essential genes (which could be recovered as heterozygotes) that act in the unc-5 molecular pathway.