Effects of hormones and injury on RNA synthesis in Saturniid moths

Abstract

The present report examines the rate of RNA synthesis during the post-embryonic life of the Cecropia silkworm and other Saturniid moths. Autoradiographic determinations were made of the rate of incorporation of tritiated uridine in various tissues during normal development and in insects subjected to endocrinological and surgical manœuvres. The effects of inhibitors of RNA and protein synthesis during various stages of the life cycle were also analysed. The rate of RNA synthesis in many tissues roughly parallelled the rate of respiration during various stages of the life cycle, but there were significant differences in temporal patterns of RNA synthesis not only between tissues but within a tissue. During larval moult cycles chitogenous epithelia such as epidermis, tracheae, and foregut showed temporal patterns of RNA synthesis which correlated directly with the process of moulting. In other tissues the temporal patterns of RNA synthesis did not parallel the events of the moult cycle. The rate of RNA synthesis was higher during larval life than in any other stage. After pupation RNA synthesis decreases in most tissues and is extremely low during diapause at which time only a few tissues such as haemocytes, brain, oenocytes, Malpighian tubules, and perigonadal fat body continue to synthesize RNA at significant rates. During the first half of the pupal-adult transformation, the rate of RNA synthesis increased initially, but thereafter it decreased in many tissues. Integumentary injury to diapausing pupae stimulated RNA synthesis. A local stimulation occurred within 2 hr of injury and was characterized by intense RNA synthesis in tissues near the injury. A systemic stimulation appeared later in all of the tissues examined except the gonads. This systemic stimulation of RNA synthesis roughly paralleled the increased respiration stimulated by injury. A pupal cuticle was synthesized by the regenerating epidermis in the absence of juvenile hormone. When RNA synthesis was blocked in diapausing pupae with actinomycin D, pupae survived and continued to synthesize proteins for 24 days, suggesting that messenger RNAs survive for many days. When protein synthesis was blocked with puromycin, diapausing pupae died within 17 days. During periods of rapid RNA synthesis such as larval life, early stages of adult development and after injury, the insects were promptly killed by low doses of actinomycin. When RNA synthesis was low, such as during diapause, in late states of adult development, and during adult life, they were insensitive to large doses of actinomycin. Experiments on developing adults indicated that the mRNA for many specific developmental events was made many days prior to the event.