IDENTIFICATION OF A STEROIDOGENIC NEUROHORMONE IN FEMALE MOSQUITOS

In the female mosquito, Aedes aegypti, neurohormones are released from the brain in response to a blood meal and stimulate the ovaries to se crete ecdysteroid hormones, which modulate yolk protein synthesis in t he fat body. Neuropeptides with this bioactivity were isolated from he ad extracts, and partial sequences from these peptides when aligned ga ve a 31-residue sequence at the amino terminus. Oligonucleotide primer s for this sequence were used to amplify with the polymerase chain rea ction a genomic DNA product that hybridized to a clone from a head cDN A library. The cDNA encodes a 149-residue preprohormone that is proces sed into an 86-residue peptide, as indicated by the mass value obtaine d from the native peptide, with the expected amino-terminal sequence, After modification, the cDNA for the putative neurohormone was express ed in a bacterial system, and the purified peptide had high specific a ctivity in bioassays, thus confirming that it is a steroidogenic gonad otropin, the first to be identified for invertebrates.