The C-Terminus Shortened Analogs of the Insect Peptide Oostatic Hormone with Accelerated Activity

Shortened analogs1a–1fof the oostatic hormone1gwith a decreased number or an omission of the C-terminal Pro residues were synthesized for investigation of their effect on oogenesis in the flesh flySarcophaga bullata Parker(Diptera). Peptides1b–1gwere prepared by solid-phase synthesis on polystyrene/divinylbenzene polymer with a 2-chlorotrityl linker using Fmoc/tBu strategy in dimethylformamide (DMF). Tetrapeptide1a, devoid of all the carboxy-terminal Pro residues, was prepared by stepwise procedure in DMF solution from HCl-H-Ala-OMe using Boc-Pro-OH, Z-Asp(OtBu)-OSu, and Boc-Tyr-OSu. In general, the peptides assayed affected processes of egg development in 20–80% of ovarioles causing changes in the follicular epithelium, proliferation of its nuclei, and cell division toward the inner part of the egg chamber. This process leads to the occurrence of a multilayered follicular epithelium which later fills up almost the whole egg chamber and then degenerates. Such ovarioles are never able to produce eggs. The shortening of the peptide sequence accelerated the observed effects on egg development. The application of the125I-labeled peptides made possible to express quantitatively the time dependence of the radioactivity distribution in the insect body, including ovaries through which it is transferred to the next F1 generation. The radioactivity was measured in larvaes and, consequently, in newborn flies. For different peptide sequences applied, different radioactivity distributions in the insect body were found using the same radiolabeling.