© 1982 by The Society for Integrative and Comparative Biology
Genetically Induced Abnormalities in Drosophila: Two or Three Patterns?1
School of Life Sciences, University of Nebraska—Lincoln Lincoln, Lincoln, Nebraska 68588
SYNOPSIS. The removal of a portion of a Drosophila imaginal disc stimulates pattern regulation whereby the missing portion is regenerated or extra copies of the surviving portion (duplications and triplications) are produced. The results of recent experiments in which temperature-sensitive cell-lethal mutations were used to induce pattern regulation are considered here in an attempt to answer a major question: What is the nature of the pattern-forming system in the newly formed tissues? One current hypothesis is that the observed pattern regulation phenotypes are the result of interactions between portions of a single pattern. The evidence from studies in which Drosophila genetic investigative techniques were applied to developing leg duplications indicate that initiation and growth of the duplicate are similar or identical to normal development in terms of cell number, growth rate and pattern of cell lineage (compartments). This suggests that portions of the genetic mechanism underlying normal development may be reactivated and used to control abnormal development. Leg triplications consist of one complete set of leg structures and two partial sets arranged in a mirror symmetrical cuticular process. These processes either become more or less complete distally (they diverge or converge, respectively) by the addition or deletion of structures at the lines of symmetry. Whether a particular process diverges or converges is related to its circumferential location. These leg duplication and triplication phenotypes can be explained as the result of cell death in situ followed by interaction between the surviving portions of the original leg pattern following the rules of the polar coordinate model of positional information.