Increase in the size of the amino acid pool is sufficient to activate translation of early trypsin mRNA in Aedes aegypti midgut

Early trypsin is a female-specific protease present in the midgut of the ye llow fever mosquito Aedes aegypti during the first 4-6 h after ingestion of a blood meal. Transcription of the early trypsin gene occurs after adult e mergence under control of juvenile hormone, but the transcript remains untr anslated before feeding. Early trypsin was in vitro translated using mRNA e xtracted from midguts of unfed and fed females, indicating that there are n ot structural features in the early trypsin mRNA that impede translation in vitro. Eight single protein meals exhibiting different molecular weights a nd amino acid composition, as well as ingestion of several amino acid mixtu res of different complexity, had the ability to prompt early trypsin transl ation. In contrast, ingestion of saline, latex or midgut-filling sugars wer e unable to induce early trypsin mRNA translation. In addition intra-thorac ic injection of an amino acid solution induced early trypsin translation, w hile injection of saline or albumin failed. In summary an increase in the s ize of the midgut amino acid pool by feeding or injection of an amino acid solution was sufficient to induce translation of early trypsin mRNA; S-35-l abeled amino acids, fed with a protein meal, were incorporated into newly s ynthesized early trypsin, the first phase of trypsin synthesis is likely in duced by an initial rapid increase in the concentration of amino acids in t he midgut cells after ingestion of a blood meal. (C) 1999 Published by Else vier Science Ltd. All rights reserved.