Worm Breeder's Gazette 14(1): 50 (October 1, 1995)
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.
Department of Molecular and Cell Biology, University of California Berkeley, CA 94720
In the course of mapping gm17, an HSN-migration defective mutant isolated by Michael Basson in the Horvitz lab, we discovered that it fell under mnDp57(X) and had a similar appearance to dpy-23(e840) (a dumpy body with characteristic bulges around the head). e840 failed to complement gm17 for the Dpy phenotype; in addition, e840 has an HSN migration defect. Anti-serotonin antibody staining to observe HSN morphology showed that the HSNs migrated 53% and 46% of normal their normal distances in gm17 and e840 animals, respectively. The HSN axons, which normally extend forward to the pharyngeal nerve ring, extend rearward to the tail in 25% of gm17 animals and 40% of e840 animals. Many HSN cell migration mutants also have mild HSN axon defects, presumably because the cell body is in the wrong place relative to axon guidance cues. The dpy-23 axon defects, however, appear to be more severe and of higher penetrance than those usually observed in cell migration mutants. Nomarski optics showed that the QL cell, which normally migrates rearward, often migrated forward instead. Finally, the gonad arms frequently have abnormal reflexions, indicating a distal tip cell migration defect. The dumpy phenotype of dpy-23 animals can be maternally rescued. Examination of the HSNs of mutant progeny of heterozygous animals by Nomarski and anti-serotonin staining showed that the HSN migration defects were also usually maternally rescued. We found several animals with HSN cell bodies in the correct positions but that still had extended HSN axons rearward to the tail. This suggests that dpy-23 is specifically required for proper HSN axon guidance, and that the misrouted axons are not simply a secondary result of misplaced cell bodies. Because dpy-23 mutants are very sick, and because in the past it has been suggested that dpy-23 might be involved in dosage compensation, we were concerned that dpy-23¹s effects on cell migrations might be caused by defects in dosage compensation, by a Dpy body shape, or by general sickness. The cell bodies, however, are not misplaced in dosage compensation Dpy genes like dpy-21 or dpy-28. Furthermore, other sick Dpy mutants, such as dpy-22 or unc-119, do not have HSN migration defects. Efforts to clone dpy-23 are in progress. We have mapped dpy-23 relative to RFLPs, and have achieved single-cosmid rescue. We are now further narrowing down the rescuing region.