Experimental Cell Research 47, 97-107 (1967) 97 STUDIES ON PROTEIN SYNTHESIS IN IMAGINAL DISCS OF DROSOPHILA MELANOGASTER J. W. FRISTROM and BARBARA B. KNOWLES’ Department of Genetics, University of California, Berkeley, Calif., U.S.A. Received October 14. 1966 IN Dipteran insects a large proportion of the external adult structures are derived from imaginal discs. The discs themselves arise from the embryonic hypoderm and are carried during larval life in the body cavity as discrete masses of tissue. Each type of disc has a distinctive morphology and generally one type of disc can be readily distinguished from other types. When trans- planted to larvae, discs develop autonomously within the host larvae and undergo normal morphogenesis [a]. Hadorn [7] has summarized evidence indicating that the imaginal structures are developmentally determined in the early embryo. The basic gross morphological appearance of discs remains unchanged during the third larval instar. In the prepupa, in a matter of 3-4 hr, discs undergo distinctive morphological alterations. Thus, during this transition discs are good material for the study of morphogenesis. The present report describes studies on protein synthesis in discs of different ages. The study was undertaken in an attempt to evaluate the importance of qualitative alterations in protein synthesis during disc morphogenesis. MATERIALS AND METHODS An Oregon R stock of Drosophila melanogasfer was used. Larvae were grown in mass cultures at 25°C following the method of Mitchell and Mitchell [IO]. In experi- ments comparing protein synthesis in larval discs of different ages, flies were allowed to deposit eggs in food boxes for 4 hr intervals. Longer egg laying periods were used for comparisons of protein synthesis in larval and prepupal discs. Larvae were re- covered from food boxes by washing with water. Prepupae were recovered by dis- lodging attached prepupae from the sides and covers of the food boxes. They were suspended in distilled water and allowed to settle. Those which had developed abdominal gas bubbles floated and were discarded. The remaining prepupae were assumed to be less than 44 hr old and were used as a source of prepupal discs. Discs were isolated following the method of Fristrom and Mitchell [6]. Larger numbers of larvae were used than previously reported and the efficiency of disc recovery was 1 N.I.H. Postdoctoral Trainee. 7 - 671817 Experimental Cell Research 47