Developmental analysis of a temperature-sensitive melanotic tumor mutant inDrosophila melanogaster.

A sex-linked, temperature-sensitive melanotic tumor mutation inDrosophila melanogaster, tu (1) Sz , was mapped at 34.3±and localized to bands 10A10-11 of the polytene chromosomes. At 26°Ctu-Sz larvae develop melanotic tumors whereas 18°C is non-permissive for tumor formation. Tumorigenesis at 26°C involves the encapsulation of abnormal caudal fat body regions by precociously differentiated hemocytes. Low temperature blocks the development of the abnormal adipose cells and the overlying aberrant tissue surfaces but does not inhibit precocious differentiation of the hemocytes to the lamellocytic form. This phenotypic difference at the two temperatures indicates that lamellocyte encapsulation to form melanotic tumors is directed against abnormal tissue surfaces. On the basis of these observations and an earlier study (Rizki and Rizki 1979) we propose that hereditary melanotic tumors inD. melanogaster are a calss of autoimmune disorders in which affected tissue surfaces arouse the body's cellmediated defense response.