Worm Breeder's Gazette 11(3): 70
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.
In C. elegans, coordinated sinusoidal locomotion is mediated through six major motor neurons (DA, DB, DD, VA, VB, and VD). Four of these motor neuron classes are excitatory (DA, DB, VA, and VB), whereas, DD and VD are inhibitory motor neurons (White et al. 1986). We have previously reported that DD and VD motor neurons are brightly stained with an anti-tubulin monoclonal antibody (2-26-33) that was raised against Sea Urchin axonemes (G. Piperno, personal communications; Siddiqui, S. et al., 1969). The pattern of staining with 2-28-33 matches closely that of the staining with anti-GABA antibodies (S. McIntyre, R. Horvitz, and J. White, WBG: 9 (2), p55). Mutants with Abnormal Fasciculation of DD and VD Axons: A number of mutants affecting DD and VD neurons were previously identified by screening locomotory mutants, immunocytochemically with anti-GABA antibodies (S. McIntyre,R. Horvitz, & J. White). We did a similar screen with 2-28-33. We have screened mutants in all available 'uncoordinated' genes, immunocytochemically, on whole mount squash preparations, using 2-26-33 antibodies, and identified mutants in 15 genes with abnormal staining of DD and VD neurons. Mutations in 11 genes (unc-5, unc-6, unc-13, unc-34, unc-40, unc-51, unc-62, unc-69, unc-71, unc-73, and unc-76) affect the growth and fasciculation of the dorsalward processes of DD and VD axons. Among these, mutations in four genes (unc-5, unc-6, unc-51, and unc-69) appeared to have the most pronounced effect on the growth DD and VD dorsalward axons. The mutant axons fail to reach their normal targets in the dorsal cord, and instead veer in various lateral positions; frequently reentering the ventral cord. The cell body position of the DD and VD neurons is also abnormal in most of the stained worms. Mutants in seven genes (unc-13, unc-34, unc-40, unc-62, unc-71, unc- 73, and unc-76), display less severe abnormalities in the dorsalward axons of the DD and VD neurons, as the mutant axons eventually reach the dorsal cord through circuitous routes. Abnormal arborizations of the axons is also seen, and the cell bodies are occasionally displaced. Mutants in unc-59, and unc-55 (known to have defective cytokinesis) display multiple axonal processes emanating from the cell bodies, but they generally grow along the motor commissures. Mutants in all of the genes mentioned above harbor defects in different classes of neurons, including mechanosensory neurons, chemosensory neurons, and other motor neurons. e.g, cell body positions and axons of the touch neurons are variably abnormal. Mutants in unc-6, unc-13, unc-51, unc- 71, and unc-73, are known to affect axonal growth and placement of PHC and PVN neurons (Siddiqui and Culotti, unpublished, Siddiqui, 1989). Axonal guidance of the PHA and PHB neurons of unc-6, unc-13, unc-51, unc-73, and unc-76 mutants is abnormal(Hedgecock et al. 1985, Siddiqui, 1989). Mutants in unc-6, unc-34, unc-40, unc-51, unc-71, unc-73, and unc-76 are known to affect the axonal outgrowth of the hermaphrodite specific neuron (HSN) (Desai, et al. 1988). These observations suggest that different neuron types are specified by a combination of genes that are activated in different cell types. Comparison of 2-28-33 Staining with Anti-GABA Staining: Due to differential requirements for fixation, double labeling with 2-28-33 and anti-GABA antibodies has proven difficult. However, we find DD, VD, and RME cells stain very brightly with both antibodies ( Siddiqui et al. 1989). In addition, we find two cells in the head that stain faintly with 2-28-33. The cell body position (doubly stained with Hoechst dye) suggests that these cells are RIS and AVL. However, this identification is tentative and begs confirmation with either laser ablation of the RIS and AVL neurons or use of mutants that may eliminate or overproduce these neurons. We are more definite about DVB, a neuron located in the dorsorectal ganglion; by staining lin-4 mutant animals with either 2-28-33,or anti-GABA antibodies. In 40% of the stained mutant animals, multiple (2 or 3) DVB cells are apparently stained. The major difference in the staining pattern of 2-28-33 and anti- GABA antibodies is in unc-30 mutants. Anti-GABA antibodies fail to stain the cell bodies and the axonal processes of the DD and VD neurons, whereas, 2-28-33 antibodies stain DD and VD neuronal cell bodies in most of the stained animals. The mutant cell bodies are, however, stained less brightly than in the wild type, and their disposition is abnormal along the ventral nerve cord. The DD and VD axons fail to stain with 2-28-33 in unc-30 mutants, but the RME and DVB cells apparently stain normally. Mutants in unc-25 lack staining of both the cell bodies and the axonal processes of DD and VD neurons, with either anti-GABA or 2-28- 33 antibodies. Mutants in unc-47 and unc-43 that show enhanced and reduced staining, respectively, with anti-GABA abs., seem to show normal staining with 2-28-33 antibodies. Several alleles for each gene were screened in the immunocytochemical studies, except when only one allele is available. At least one hundred well stained animals were scored for each mutant class.