Luteinising hormone, follicle stimulating hormone and gonadotropin releasing hormone immunoreactivity in two insects: Locusta migratoria migratoroides R&F andSarcophaga bullata(Parker)

Gonadotropins in insects: an overview

Control of gonad development in insects requires juvenile hormone, ecdysteroids, and a peptidic brain gonadotropin(s). Compared to vertebrates, the situation in insects with respect to the molecular structure of gonadotropins is far less uniform. Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) of vertebrates are glycoproteins that are synthezised in the hypothalamus and released from the anterior pituitary. They stimulate gonad development, the production of progesterone or of sex steroids (estrogens, androgens). None of the known insect gonadotropins is a glycoprotein, neither can they be grouped into a single peptide family. In Drosophila, two G-protein coupled receptors, structurally related to the mammalian glycoprotein hormone receptors, have been identified. Nothing is known about their natural ligands. The sex-steroids of insects are likely to be ecdysteroids (20E in females, E in males of some species). Some of the identified gonadotropins speed up vitellogenesis (locust OMP and some -PF/-RFamide peptides) or stimulate ecdysteroid production by the ovaries (locust-OMP and Aedes- OEH) or testis (testis ecdysiotropin of Lymantria). In flies, the only as yet identified gonadotropin is the cAMP-generating peptide of Neobellieria. The seeming absence of uniformity in gonadotropins in insects might be due to a multitude of factors that can stimulate ecdysteroid production and/or to the use of different bioassays. Arch.

Isolation of NEB-LFamide, a novel myotropic neuropeptide from the grey fleshfly

A methanolic extract of 350,000 adult grey fleshflies Neobellieria bullata, was prepared and screened for myotropic activity. After fractionation on the first column, all fractions were screened in two heterologous (Locusta oviduct and Leucophaea hindgut) and one homologous (Neobellieria hindgut) myotropic bioassay. We here report the purification of one fraction, which stimulates the contractions of the Locusta oviduct. Electrospray Mass Spectrometry of the peptide revealed a molecular mass of 1395.82. The primary structure has been determined as AYRKPPFNGSLF-amide. This novel peptide was designated Neb-LF-amide. This sequence is different from the other known myotropic peptides in insects. The threshold concentration of the synthetic peptide is 1 x 10(-7) M on the Locusta oviduct. On the hindgut of Neobellieria or Leucophaea, the synthetic peptide is not active. By use of a polyclonal antiserum raised against the synthetic peptide, immunoreactivity was localized in median neurosecretory cells in the pars intercerebralis of the fly brain, indicating that Neb-LF-amide is a neuropeptide.

Folliculostatins, gonadotropins and a model for control of growth in the grey fleshfly, Neobellieria (sarcophaga) bullata

The sequences of two folliculostatic peptides of the fleshfly Neobellieria bullata have been determined recently. The first peptide (Neb-TMOF: H-NPTNLH-OH), originates from a 75 kDa precursor protein found in vitellogenic oocytes. The hexapeptide directly inhibits the synthesis of trypsin-like enzymes in the gut, and thus lowers the concentration of yolk polypeptides in the hemolymph. It also inhibits the biosynthesis of ecdysone in the larval ring gland. Therefore, it could also be named prothoracicostatic hormone (Neb-PTSH). The second peptide (Neb-colloostatin: H-SIV-PLGLPVPIGPIVVGPR-OH) acts on previtellogenic follicles and is a cleaved product of a collagen-like precursor molecule. Our results indicate that peptides that are cleaved from matrix proteins could act as growth-inhibiting factors. Gonadotropin releasing hormone (GnRH)-immunolike peptides were not identified, but progress is being made in the isolation and characterization of factors which stimulate cAMP production by the ovary. Using these results, a novel model of growth control in which matrix proteins play an important role as a potential source of growth regulators has been developed.