Puffing of Salivary Gland Chromosomes after Treatment with Carbon Dioxide

Abstract

AFTER larvae of the Oregon R strain of Drosophila melanogaster had been placed in an atmosphere of CO₂ for 1 h late in the third instar, the salivary-gland chromosomes were examined and compared with those of a similar group of the same age. The chromosomal regions studied were eight regions known to puff: 85–86, 93, and 95 on the right arm of the third chromosome; 66, 71–72, 74–75, and 78 on the left arm of the same chromosome; and 2B on the X chromosome. The size of the puffs in the 84 glands examined were arbitrarily divided into four classes from smallest to largest and the data tabulated accordingly (Table 1). Although not all puffs were larger in the groups treated, the mean size of puffs III R 85–86, 93, and 95, and III L 66 was larger after exposure to CO₂. The remainder showed no tendency to enlarge after such treatment. Larvae late in the third instar not used for chromosomal studies survived and developed into adults following the exposure to CO₂. Many younger larvae died. These observations are reported because of current interest in the puffing pattern as presumed indication of localized production of RNA in response to hormonal stimulation. Recently we have found that ecdysone will produce puffing at this stage of larval development in some regions but not in others. Two not affected by CO₂ (I 2B and III L 74–75) showed an increase in mean size with ecdysone, and one (III L 71–72) failed to respond to either treatment.