Worm Breeder's Gazette 8(3): 51
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 ALM neurons are located on the sides of the animal somewhat anterior to the gonad. They are embryonic sisters of the BDU neurons located nearer the head. In the wild type, the ALM/BDU mother cell divides fairly late (430 min) and the ALM daughter migrates posterior to its final position. The ALM extends a process anteriorly along the edge of the dorsal body muscles and the cell body rests against the muscle edge in newly hatched larvae. In the homeotic mutant lin-32( e1926), the ALM cell bodies are displaced anterior of their normal position. In a small fraction of the neurons, the cell bodies are located against the ventral muscle edge and extend a process anteriorly along it. Some of these ventral processes switch again to the dorsal muscle edge as they approach the nerve ring but most remain ventral. The ALM neurons in early L1 larvae are usually positioned laterally and near BDU. We speculate that they differentiate later than normal. Cynthia Kenyon (previous Newsletter) has found that the Q/V5 mother cell divides late in this mutant. Conceivably the ALM/BDU division is similarly delayed. In any event, the ALM neurons appear able to grow along the ventral muscle edge as a second choice to their normal path. The PLM neurons are located in the tail and normally extend axons anteriorly along the ventral muscle edges. The PLM cell bodies are displaced anteriorly in lin-32(e1926) mutants perhaps reflecting delayed maturation. No misplaced PLM axons were observed. M. Chalfie (personal communication) has found a new lin-32 allele that apparently blocks the birth or differentiation of the PLM neurons completely. The PLM axons in unc (rh34) mutants sometimes extend along the dorsal muscle edge. These displaced processes appear to extend forward for their normal distance and stop somewhat before the ALM cell body. In a few animals, we have followed the displaced processes back into the tail where they have ended in exceptionally large soma. The rh34 mutant has not been mapped but its phenotype, blocked cytokinesis in certain postembryonic lineages, closely resembles the published description of unc-59 mutants (Sulston and Horvitz, 1981). We speculate that certain late embryonic cell divisions also fail in rh34 including the PLM/ALN division. Interestingly, the ALN axon normally arows along the dorsal muscle edge. We speculate that when the division fails, a hybrid cell is formed with the distinctive process specializations of the PLM neuron but the dorsal preference of the ALN neuron. In lin-30 (e1908; LGIII) mutants, cytokinesis fails in many late embryonic and postembryonic divisions including the ALM/BDU division. In rare animals where this division occurs. the ALM and BDU neurons are normal. We have not yet looked at the axons in the blocked cells but such cells remains lateral at the normal BDU position. [See Figure 1]