Worm Breeder's Gazette 12(3): 40 (June 15, 1992)

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.

Touch Neuron Axons Go Dorsal

Michel Hamelin, Youwen Zhou, Ian Scott, Joe Culotti

The Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada M5 G1X5

The unc-5 gene encodes a novel cell adhesion receptor of the immunoglobulin super family which is required to guide dorsal migrations of neuron growth cones on the epidermis ( UNC-5 ;Neuron 4:61; Leung-Hagesteinj et al.,submitted). unc-5 has been shown genetically to require unc-6 ,which encodes a putative epidermal guidance cue, for its guidance functions (Neuron 4:61).

The neurons mostly affected by unc-5 mutations are the motor neurons DA, DB, DD, AS, and VD. unc-5 has been shown to act cell autonomously in these cells (WBG 12[1]:32). We wanted to test whether unc-5 expression in neurons that do not normally grow dorsally on the epidermis would suffice to steer them in a dorsal direction

The six touch receptor neurons normally extend axons ventrally or longitudinally on the epidermis. These trajectories are not affected by unc-5 mutations. The mec- 7 tubulin gene promoter has been shown to express lacZ specifically in the touch neurons (WBG 11[3]:40; Hamelin et al., in press). A fusion gene was made with the mec-7 promoter and the entire unc-5 coding region. This mec-7 - unc-5 construct was injected in the germline of wild type animals, along with a mec- 7-lacZ construct (WBG 11[3]:40), and pRF4 (WBG 11[1]:18). Transgenic animals were stained with X-Gal to reveal their touch neuron axons. Virtually all detectable axons (376/378) were found to be dorsally re-directed. The cell bodies were often displaced, mostly dorsally, but sometimes anteriorly (AVM, ALMs, PLMs) or posteriorly (PVM). Most transgenics were also touch insensitive.

If UNC-5 induces dorsal trajectories in the touch neurons by utilizing its normal guidance functions, then these abnormal trajectories should depend on UNC-6 .In a null mutant of unc-6 carrying the mec-7 - unc-5 transgene, the touch neuron axons were no longer found to be misguided

Together, these results indicate that UNC-5 can act cell-autonomously, and is sufficient to steer dorsally the growth cones of neurons that normally don't.

Literature Cited:

Neuron 4:61

WBG 12[1]:32

WBG 11[3]:40

Hamelin et al., in press

WBG 11[1]:18