Gonadotropins in insects: An overview

Control of gonad development in insects requires juvenile hormone, ecdyster oids, and a peptidic brain gonadotropin(s). Compared to vertebrates, the si tuation in insects with respect to the molecular structure of gonadotropins is far less uniform. Follicle Stimulating Hormone (FSH) and Luteinizing Ho rmone (LH) of vertebrates are glycoproteins that are synthezised in the hyp othalamus and released from the anterior pituitary. They stimulate gonad de velopment, the production of progesterone or of sex steroids (estrogens, an drogens). None of the known insect gonadotropins is a glycoprotein, neither can they be grouped into a single peptide family. In Drosophila, two G-pro tein coupled receptors, structurally related to the mammalian glycoprotein hormone receptors, have been identified. Nothing is known about their natur al ligands. The sex-steroids of insects are likely to be ecdysteroids (20E in females, E in males of some species). Some of the identified gonadotropi ns speed up vitellogenesis (locust OMP and some -PF/-RFamide peptides) or s timulate ecdysteroid production by the ovaries (locust-OMP and Aedes- OEH) or testis (testis ecdysiotropin of Lymantria). In flies, the only as yet id entified gonadotropin is the cAMP-generating peptide of Neobellieria. The s eeming absence of uniformity in gonadotropins in insects might be due to a multitude of factors that can stimulate ecdysteroid production and/or to th e use of different bioassays. (C) 2001 Wiley-Liss, Inc.