Laser ablation of persistent twist cells in Drosophila: muscle precursor fate is not segmentally restricted

In Drosophila the precursors of the adult musculature arise during embryoge nesis. These precursor cells have been termed Persistent Twist Cells (PTCs) , as they continue to express the transcription factor Twist after that gen e ceases expression elsewhere in the mesoderm, In the larval abdomen, the P TCs are associated with peripheral nerves in stereotypic ventral, dorsal, a nd lateral clusters, which give rise, respectively, to the ventral, dorsal, and lateral muscle fiber groups of the adult, We tested the developmental potential of the PTCs by using a microbeam laser to ablate specific cluster s in larvae. We found that the ablation of a single segmental PTC cluster d oes not usually result in the deletion of the corresponding adult fibers of that segment. Instead, normal or near normal numbers of adult fibers can f orm after the ablation, Examination of pupae following ablation showed that migrating PTCs from adjacent segments are able to invade the affected segm ent, replenishing the ablated cells. However, the ablation of homologous PT Cs in multiple segments does result in the deletion of the corresponding ad ult muscle fibers. These data indicate that the PTCs in an abdominal segmen t can contribute to the formation of muscle fibers in adjacent abdominal se gments, and thus are not inherently restricted to the formation of muscle f ibers within their segment of origin.