Worm Breeder's Gazette 5(2): 21
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.
During a Nomarski screen of the mab (male abnormal) mutants, John Sulston noticed that there were anterior Q daughters on the left side of mab-5(e1239) animals. (Normally, the daughters of Q2 (right) are anterior, those of Q1 are posterior - see Sulston and Horvitz, Develop. Biol. 56: 110-156, 1977.) By following the Q lineages in mab-5, I've found that the defect is caused by the inappropriate migration of the Q1 progeny (toward the head instead of the tail). This places the lineage anywhere from near the vulva to the anterior position of the Q2 progeny. Among the cells made by these lineages are the two ventral microtubule cells: Q2.paa,.the anterior ventral microtubule c.?ll (AVM) , and Q1.paa, the posterior ventral microtubule cell (PVM) (see Fig. 1 in Chalfie and Thomson, J. Cell Biol. 82: 278-289, 1979). Although these cells have many common features, they differ in that l) Q2.paa is more anterior, 2) only Q2.paa grows an added branch into the nerve ring, 3) only Q2.paa makes synapses with the major ventral cord interneurons (via the extra branch), and 4) Q2.paa, but not Q1.paa, is sufficient to give a touch response when all the other microtubule cells (the touch receptors) are killed with the laser. To test whether these differences result from the different placement of the cells, one would like to alter their positions. The mab-5 mutation, in effect, does this. If Q1.paa is made near the vulva in the mutant, it has a microtubule cell process that goes further anterior than the wild type process (almost to the rear bulb of the pharynx), but it does not have the added branch and it is not functional on its own. However, when Q1.paa is produced near to the position of Q2.paa (i.e. even microtubule-containing process grows past the nerve ring). Under these conditions, it has the added branch and is functional. Q1.paa, thus, becomes more like Q2.paa. In another experiment, laser debris was created in the migration path of the wild type Q2 cell. With its migration blocked, Q2 divided posterior to the vulva. Although the E. M. hasn't been done yet, it is known that Q2.paa is not functional. It appears that the correct positioning of Q2.paa is also important for its differentiation. Thus, the growth of the extra branch and, probably, the formation of synapses are under some position-dependent regulation. Other features may not be dependent on position, e.g. the length of the microtubule-containing process.