Neuroendocrine factors affecting the steady-state levels of early trypsin mRNA in Aedes aegypti

Transcription of the early trypsin gene occurs in the midgut after adult emergence under control of juvenile hormone (JH). We tested the hypothesis that factors that affect the steady-state levels of early trypsin mRNA do so by influencing the levels of JH. We investigated the effect of ingesting different meals on early trypsin mRNA levels as well as on JH levels. We also studied how early trypsin mRNA levels changed when the midgut was isolated from different components of the neuroendocrine system by abdominal ligation and decapitation. Early trypsin transcripts levels are high in unfed females; feeding different meals had three distinct effects on the changes of steady-state levels of early trypsin mRNA: (1) blood and protein meals caused the level to decrease drastically and remained low for at least 24 h; (2) amino acid meals caused a transient decrease in the mRNA level, but it returned to high levels after 12-18 h; and (3) sugar, latex and saline meals had no effect on the early trypsin mRNA steady-state levels. The changes in JH levels after ingesting blood and amino acid meals show profiles resembling the changes in early trypsin mRNA levels for the corresponding meal. Decapitation at 1, 2 and 3 days after emergence does not affect the steady-state levels of early trypsin in unfed females. In contrast, 24 h after feeding, transcript levels were significantly higher in decapitated females when compared with non-decapitated fed females. We propose that the changes in the steady-state levels of early trypsin mRNA observed after the ingestion of different meals, ligations and decapitations are generated by changes in the levels of juvenile hormone.