Worm Breeder's Gazette 13(3): 81 (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.

The unc-40 axon guidance gene encodes a transmembrane receptor with extracellular fibronectin and immunoglobulin domains.

Shirley Chan[1], Ming-Wan Su[1], Hong Zhang[1], Joe Culotti[1], Ed Hedgecock[2]

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

unc-40 primarily affects ventrally oriented pioneer growth cone and cell migrations that occur on the epidermis. unc-40 also has minor effects on dorsally oriented pioneer migrations (Hedgecock et al., Neuron 4:61-85,1990). We mapped unc-40 relative to strain-specific DNA polymorphisms, then rescued the Unc and DTC defects by germline transformation with a cosmid and with a 14 kb phage from the region. Based on germline transformation experiments using overlapping cosmid and phage clones, we were able to identify a region required for rescue that encodes a single transcript by Northern analysis of 5.5 kb. We cloned and sequenced a 4.2 kb cDNA (S. Kim library) corresponding to this transcript. This cDNA contains a 3.3 kb open reading frame. The predicted unc-40 protein (so far) has a single hydrophobic transmembrane domain, six fibronectin type III (FNIII) domains and two immunoglobulin (IG) domains. FNIII and IG domains are found in a variety of transmembrane proteins, but these most commonly have three or five FNIII domains. Several transmembrane proteins that have extracellular IG and FNIII domains also have intracellular tyrosine kinase or phosphotyrosine phophatase domains, but the predicted 309 residue intracellular region of unc-40 has no obvious similarity to these domains.

We are currently sequencing genomic DNA to identify the 5' end of unc-40 .Northern and Southern analyses have failed to reveal detectable deletions or rearrangements in a dozen unc-40 mutants analyzed.

In addition to affecting migrations on the dorsoventral coordinates of the epidermis, unc-40 mutations also affect body shape, normally an epidermal function. To determine where unc-40 is expressed and where it is required for guidance, we are constructing strains to do mosaic analysis and to analyze patterns of expression from the unc-40 promoter.