Coexistence of natural enemies in a multitrophic host–parasitoid system

Abstract.  1. This study explored the temporal and spatial aspects of coexistence over many generations in a multispecies host–parasitoid assemblage.
2. The long-term interaction between the cabbage root fly, Delia radicum (Diptera: Anthomyiidae), and two of its natural enemies, Trybliographa rapae (Hymenoptera: Fitigidae) and Aleochara bilineata (Coleoptera: Staphylinidae), in a cultivated field at Silwood Park over 19 years was explored.
3. Although time series showed that the populations were regulated, the impact of the natural enemies was highly variable. Within-year determinants showed that the spatial response of the specialist parasitoid, T. rapae , was predominantly independent of host density while A. bilineata acted simply as a randomly foraging generalist parasitoid.
4. These findings are compared and contrasted with an earlier investigation of the same system when only the first 9 years of the time series were available. This study demonstrated the potential of long-term field studies for exploring hypotheses on population regulation, persistence, and coexistence.     

Heparin binds to Leishmania donovani promastigotes and inhibits protein phosphorylation.

We show that promastigotes of Leishmania donovani, the causative agent of visceral leishmaniasis (kala-azar), possess heparin receptors on their surface. From a linear Scatchard plot of the binding data obtained using [3H]heparin and viable promastigotes, one derives a binding constant of 4.7 x 10(-7) M and an estimate of 860,000 receptors per parasite. The [3H]heparin bound to parasites could not be displaced by hyaluronic acid or by three other glycosaminoglycans (dermatan sulphate, chondroitin 4-sulphate and chondroitin 6-sulphate). It was demonstrated that exponential phase promastigotes growing in medium 199 supplemented with fetal bovine serum incorporate 35SO4 into a cell-associated macromolecule that has the properties of heparin proteoglycan. Heparin inhibits the activity of the cell-surface histone-protein kinase; incubation of viable promastigotes with [gamma-32P]ATP and MgCl2 (10 mM) in the absence and presence of heparin (0.01-0.5 mg/ml) for 10 min, followed by analysis by SDS/polyacrylamide-gel electrophoresis and autoradiography, revealed that the phosphorylation of 12 or 13 parasite proteins was inhibited by the glycosaminoglycan. These data suggest that heparin may play a role in the host-parasite relationship.     

Glomerular basement membrane proteoglycans are derived from a large precursor

The basement membrane heparan sulfate proteoglycan produced by the Englebreth-Holm-Swarm (EHS) tumor and by glomeruli were compared by immunological methods. Antibodies to the EHS proteoglycan immunoprecipitated a single precursor protein (Mr = 400,000) from [35S]methionine-pulsed glomeruli, the same size produced by EHS cells. These antibodies detected both heparan sulfate proteoglycans and glycoproteins in extracts of unlabeled glomeruli and glomerular basement membrane. The proteoglycans contained core proteins of varying size (Mr = 150,000 to 400,000) with a Mr = 250,000 species being predominant. The glycoproteins are fragments of the core protein which lack heparan sulfate side chains. Antibodies to glomerular basement membrane proteoglycan immunoprecipitated the precursor protein (Mr = 400,000) synthesized by EHS cells and also reacted with most of the proteolytic fragments of the EHS proteoglycan. This antibody did not, however, react with the P44 fragment, a peptide situated at one end of the EHS proteoglycan core protein. These data suggest that the glomerular basement membrane proteoglycan is synthesized from a large precursor protein which undergoes specific proteolytic processing.     

Identification of cDNA clones encoding different domains of the basement membrane heparan sulfate proteoglycan

We have used antibodies to the basement membrane proteoglycan to screen lambda gt11 expression vector libraries and have isolated two cDNA clones, termed BPG 5 and BPG 7, which encode different portions of the core protein of the heparan sulfate basement membrane proteoglycan. These clones hybridize to a single mRNA species of approximately 12 kilobases. Amino acid sequences obtained on peptides derived from protease digests of the core protein were found in the deduced sequence, confirming the identity of these clones. BPG 5 spanned 1986 base pairs and has an open reading frame of 662 amino acids. The amino acid sequence deduced from BPG 5 contains two cysteine-rich domains and two internally homologous domains lacking cysteine. The cysteine-rich domains show homology to the cysteine-rich domains of the laminin chains. A globule-rod structure, similar to that of the short arms of the laminin chains, is proposed for this region of the proteoglycan. The other clone, BPG 7, is 2193 base pairs long and has an open reading frame of 731 amino acids. The deduced sequence contains eight internal repeats with 2 cysteine residues in each repeat. These repeats show homology to the neural-cell adhesion molecule N-CAM and the plasma alpha 1B-glycoprotein. Looping structures similar to these proteins and to other proteins of the immunoglobulin gene superfamily are proposed for this region of the proteoglycan. The sequence DSGEY was found four times in this domain and could be heparan sulfate attachment sites.