Worm Breeder's Gazette 8(3): 33
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 lin-22(n372) males (B. Fixsen and R. Horvitz, 1), V2-V5 and sometimes V1 generate rays instead of body seam cells. (The cells undergo a V5-like lineage, in which Vn.pppa as well as Vn.pppp usually produces a ray.) In the wild type, the generation of V rays requires mab-5 activity. Examining the requirement for mab-5 activity in ray production in lin-22(n372) males has led to some surprising and significant conclusions. Body seam cells generate alae, which are easy to score using Nomarski optics. I have measured the extent and position of alae in lin-22(n372) males carrying different numbers of mab-5+ genes copies. The animals were grown at 15 C. 1. In lin-22(n372) males with three (or four) copies of mab-5+, alae are generally absent, or present only in the head. The mab-5 dosage was increased by using sDp3 III, a free duplication very kindly provided by R. Rosenbluth and D. Baillie. 2. In lin-22 males (two copies of mab-5 ), alae overlie the head and often the V1 region. Occasionally patches of alae are present posterior to V1. 3. In mab-5(e1239)/+,lin-22(n372) males (one copy of mab-5+), alae usually extend into the V2 and sometimes the V3 region. In addition, patches of alae are more often present posteriorly. 4. In mab-5,lin-22 males (no mab-5+ copies) alae extend along most of the body, with some gaps in the posterior. V lineages have been determined in several mab-5;lin-22 males. In these animals, as in lin-22 males, the V cells usually divided to produce two seam cells following L2 lethargus. Cells located in the anterior (and sometimes posteriorly), generated body seam cell descendants, which produced alae. Posterior seam cells often generated rays, with no overlying alae. In addition, cells that could not easily be classified as body or tail seam cells sometimes were produced. These cells generally produced faint (or no) alae. A preliminary but possibly important observation is that Vn.pppp cells have shown a greater tendency to produce rays than Vn.pppa cells. These results are significant for two reasons. First, they demonstrate that in lin-22 mutants, the decision to produce rays instead of body seam cells is influenced by the level of mab-5 activity. The probability of any V descendant adopting a ray instead of a body seam fate can be increased by raising or decreased by lowering the level of mab-5 activity. Thus, mab-5 can act as a developmental switch in lin-22 animals, and probably in the wild type as well. Second, in each of the four mutant strains described above, posterior cells are more likely to produce rays than anterior cells. Each increase in mab-5 dosage increases the anterior extent of ray production. This suggests 1) that in the wild type the level of mab-5 activity defines the size of the posterior ray domain, and 2) that at least one component of the mab-5 regulatory circuit is present in a graded distribution among the seam cells. This graded signal need not be mab-5 itself, and in principle could be generated within the V lineages or externally.