AbstractThe expression of alaserpin, a serine protease inhibitor, was studied in the developing adult olfactory system ofManduca sexta. Alaserpin mRNA in the antenna was identical to alaserpin from larval fat body, by restriction mapping and partial sequencing of clones isolated from a male pupal stage 6 antennal cDNA library. Northern and primer extension analysis showed that alaserpin transcripts were the same length at all stages and were present at stages 3 and 6, declined at stages 9–15, reappeared at stage 18, and persisted in adults. Western blotting revealed that alaserpin was present at stages 3–12, declined at stage 15, and disappeared at stage 18 and in adults. Immunocytochemistry at stage 6 revealed labeled cells closely associated with neurite bundles and scattered throughout the receptor cell layer. An occasional cell was seen in the antennal lumen. Labeled cells were segmentally distributed along the length of the antenna. The results suggest that alaserpin may have a role in antennal morphogenesis and olfactory neuron axon outgro