Cytochemistry of the differentiating flight muscles of the desert locust Schistocerca gregaria.

Cytochemical changes in the metathoracic dorsal longitudinal flight muscle of the female desert locust, Schistocerca gregaria, during its differentiation from the last day of the fourth larval instar, through the fifth larval instar up to the eighth day after the imaginal moult were examined with respect to: (1) DNA content, (2) transcriptional activity, (3) degree of chromatin condensation, (4) RNA content, (5) protein content and (6) cross-secetional fibre area. Microspectrophotometric analysis of Feulgen-stained nuclei shows that polyploidization is not a phenomenon associated with the differentiation of these muscles. The nuclei remain diploid throughout the developmental period. By "staining" with 3H-Actinomycin D, followed by autoradiography, the changes in transcriptional activity coincedent with flight muscle development were examined. At the beginning of the developmental period the transcriptional activity is relatively high and remains so up until about the middle of the fifth instar after which time it declines fairly steadily. These changes in transcriptional activity are accompanied by changes in the degree of chromatin condensation. Generally, the periods of high transcriptional activity exhibit less condensation of the chromatin. The originally high transcriptional activity is accompanied by a steady over-all increase in total RNA content during the developmental period; and in turn a large increase in total protein content. The cross-sectional area of the muscle fibres increases significantly during the growth and differentiation of the flight muscles.