Isolation and Identification of Neuropeptides in Locusta Migratoria
By means of high performance liquid chromatography (HPLC) using 4 columns with different separation characteristics, 44 neuropeptides were isolated from the migratory locust, Locusta migratoria, starting from an extract of 9000 brain-corpora cardiaca-corpora allata-suboesophageal ganglion complexes. A heterologous bioassay, based on the motility of the isolated hindgut of Leucophaea maderae was used to monitor active fractions during the purification steps. 32 hindgut stimulating and 12 hindgut inhibitory peptide fractions were isolated in a pure form. The amino acid sequences of 10 of the isolated locust peptides were established, belonging to at least three distinct families. The primary structures of some of the isolated peptides resemble vertebrate peptide hormones like gastrin, cholecystokinin and tachykinins which are known to stimulate contractions of vertebrate smooth muscle. The sequence homologies and analogous myotropic activities in insects and vertebrates substantiate evidence for a widespread and early evolution of these peptides. In an alternative approach the possibilities of recombinant DNA technology for unravelling the structures of insect neuropeptides are being investigated. A cDNA expression library (lambda gt11) was prepared starting with mRNAs from brains of Locusta. Screening was done by means of antisera directed against peptide hormones. Transformed bacterial clones synthesized molecules immunologically related to bovine growth hormone, amphibian melanophore stimulating hormone, hypertrehalosaemic factor II (Caraustus) and caudo-dorsal cell hormone (Lymnea). So far, no spectacular base sequence homologies with the “authentic materials” have been observed.
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