Activation of Balbiani ring genes in Chironomus tentans after a pilocarpine-induced depletion of the secretory products from the salivary gland lumen

Abstract

The synthesis of protein and RNA has been studied in Chironomus salivary glands after pilocarpine-induced depletion of secretory products from the gland lumen. Emptied glands showed a more than fourfold enhancement of protein synthesis, the secretory proteins being the main product. The large chromosomal puffs, Balbiani ring 1 (BR 1) and Balbiani ring 2 (BR 2), likely to be responsible for the production of messenger RNA for the secretory proteins, expanded to a considerable extent and the synthesis of the corresponding RNA species, 75 S RNA, increased fivefold after a 5-h pilocarpine treatment. In vitro experiments suggest that pilocarpine does not exert its effect on the expression of the BR genes via a direct action on the salivary gland cells themselves. The effect is more likely to result from stimulation of the retractor muscles (near the secretory duct), regulating the discharge of the secretory products from the gland lumen and, consequently, also the amount of secretory products present in the gland lumen at any given moment.