Isolation and characterization of temperature-sensitivelethal(2)giant larva alleles : II. Temperature-sensitive expression of the imaginal disc neoplasm.

In this paper we present an analysis of the behavior ofl(2)gl imaginal wing discs during culture in adult hosts. Thel(2)gl larvae reared at 29° C contain two types of wing discs, those that are morphologically normal and those that are abnormal. When discs of both types are cultured in adult hosts at 29° C, the restrictive temperature, they give rise to transplantable neoplastic tissue. However, when the 29° C reared discs are cultured at 15° C, the permissive temperature, the morphologically normal discs maintain their morphology, but the morphologically abnormal discs give rise to neoplasms. Thel(2)gl larvae reared at 15° C contain only morphologically normal discs. When these discs are cultured in adult hosts at 29° C they give rise to neoplasms, however if the discs are cultured at 15° C they maintain their normal morphology. These results demonstrate: (1) that all wing imaginal discs obtained from 29° C rearedl(2)gl larvae are competent to undergo neoplastic development, (2) the morphologically abnormal discs obtained from the 29° C rearedl(2)gl larvae are committed to neoplastic development, (3) the neoplastic development of the morphologically normal discs is temperature dependent, (4) once the neoplastic development of thel(2)gl discs has been initiated the process is not readily reversible. In addition, the ability ofl(2)gl wing discs to perform epimorphic regulation was tested by amputating morphologically normal permissively rearedl(2)gl wing discs and culturing both fragiments at the permissive temperature. Fragments of control wild-type discs maintained their morphology during culture at the permissive temperature. However, both fragments of txel(2)gl discs became neoplastic. This result is discussed with respect to a possible role for thel(2)gl function in epimorphic regulation and with respect to the phenomena of tumor promotion in vertebrates.