Isolation and characterization of temperature-sensitivelethal (2) giant larva alleles : I. Mutagenesis and larval pathology.

EMS induced temperature-sensitivelethal (2) giant larva, 1(2)gl, alleles were isolated by screening against a knownl(2)gl allele. Analysis of the lethal phase of thel(2)gl -deficiency heterozygotes demonstrated: (1) the majority of thel(2)gl larvae survive to late third instar, (2) at 29°C the majority of thel(2)gl larvae failed to pupate and only rarely did they differentiate adult cuticular structures, (3) at 15°C the majority of the larvae pupated and frequently differentiated adult cuticular structures. Examination of the imaginal discs ofl(2)gl larvae reared at 29°C revealed the presence of morphologically abnormal wing, haltere and leg imaginal discs. No morphologically abnormal discs were found in thel(2)gl larvae reared at 15°C. Studies on both the histology and the developmental capacity of the morphologically normal and abnormall(2)gl discs were performed. The morphologically normal discs are histologically normal and produce a full complement of adult cuticular structures. However, the morphologically abnormal discs contained both regions that maintained the normal monolayer epithelium and regions that had lost the normal tissue architecture. The implants obtained when the morphologically abnormal discs are injected into metamorphosing larvae contained only a limited number of the normal complement of adult structures and usually only structures found in the ventral wing hinge region were recovered. In addition, the "metamorphosed" morphologically abnormal discs contained undifferentiated tissue that gave rise to transplantable neoplasms when cultured in adults. The results of the studies on the pathology of thel(2)gl larvae are discussed with respect to the role of thel(2)gl function during normal development, the autonomy of the neoplastic development of thel(2)gl tissues, and similarities between neoplastic development inDrosophila and mammals.