Cloning and characterisation of Schistosoma japonicum insulin receptors

Background

Schistosomes depend for growth and development on host hormonal signals, which may include the insulin signalling pathway. We cloned and assessed the function of two insulin receptors from Schistosoma japonicum in order to shed light on their role in schistosome biology.

Methodology/Principal Findings

We isolated, from S. japonicum, insulin receptors 1 (SjIR-1) and 2 (SjIR-2) sharing close sequence identity to their S. mansoni homologues (SmIR-1 and SmIR-2). SjIR-1 is located on the tegument basal membrane and the internal epithelium of adult worms, whereas SjIR-2 is located in the parenchyma of males and the vitelline tissue of females. Phylogenetic analysis showed that SjIR-2 and SmIR-2 are close to Echinococcus multilocularis insulin receptor (EmIR), suggesting that SjIR-2, SmIR-2 and EmIR share similar roles in growth and development in the three taxa. Structure homology modelling recovered the conserved structure between the SjIRs and Homo sapiens IR (HIR) implying a common predicted binding mechanism in the ligand domain and the same downstream signal transduction processing in the tyrosine kinase domain as in HIR. Two-hybrid analysis was used to confirm that the ligand domains of SjIR-1 and SjIR-2 contain the insulin binding site. Incubation of adult worms in vitro, both with a specific insulin receptor inhibitor and anti-SjIRs antibodies, resulted in a significant decrease in worm glucose levels, suggesting again the same function for SjIRs in regulating glucose uptake as described for mammalian cells.

Conclusions

Adult worms of S. japonicum possess insulin receptors that can specifically bind to insulin, indicating that the parasite can utilize host insulin for development and growth by sharing the same pathway as mammalian cells in regulating glucose uptake. A complete understanding of the role of SjIRs in the biology of S. japonicum may result in their use as new targets for drug and vaccine development against schistosomiasis.

Cloning and expression of the large zebrafish protocadherin gene, Fat

The cadherin superfamily members play an important role in mediating cell-cell contact and adhesion (Takeichi, M., 1991. Cadherin cell adhesion receptors as a morphogenetic regulator. Science 251, 1451-1455). A distinct subfamily, neither belonging to the classical or protocadherins includes Fat, the largest member of the cadherin super-family. Fat was originally identified in Drosophila. Subsequently, orthologues of Fat have been described in man (Dunne, J., Hanby, A. M., Poulsom, R., Jones, T. A., Sheer, D., Chin, W. G., Da, S. M., Zhao, Q., Beverley, P. C., Owen, M. J., 1995. Molecular cloning and tissue expression of FAT, the human homologue of the Drosophila fat gene that is located on chromosome 4q34-q35 and encodes a putative adhesion molecule. Genomics 30, 207-223), rat (Ponassi, M., Jacques, T. S., Ciani, L., ffrench, C. C., 1999. Expression of the rat homologue of the Drosophila fat tumour suppressor gene. Mech. Dev. 80, 207-212) and mouse (Cox, B., Hadjantonakis, A. K., Collins, J. E., Magee, A. I., 2000. Cloning and expression throughout mouse development of mfat1, a homologue of the Drosophila tumour suppressor gene fat [In Process Citation]. Dev. Dyn. 217, 233-240). In Drosophila, Fat has been shown to play an important role in both planar cell polarity and cell boundary formation during development. In this study we describe the characterization of zebrafish Fat, the first non-mammalian, vertebrate Fat homologue to be identified. The Fat protein has 64% amino acid identity and 80% similarity to human FAT and an identical domain structure to other vertebrate Fat proteins. During embryogenesis fat mRNA is expressed in the developing brain, specialised epithelial surfaces the notochord, ears, eyes and digestive tract, a pattern similar but distinct to that found in mammals.

Concurrent binding of anti-EphA3 antibody and ephrin-A5 amplifies EphA3 signaling and downstream responses: potential as EphA3-specific tumor-targeting reagents

The Eph receptor tyrosine kinases and their membrane-bound ephrin ligands form a unique cell-cell contact-mediated system for controlling cell localization and organization. Their high expression in a wide variety of human tumors indicates a role in tumor progression, and relatively low Eph and ephrin levels in normal tissues make these proteins potential targets for anticancer therapies. The monoclonal antibody IIIA4, previously used to isolate EphA3, binds with subnanomolar affinity to a conformation-specific epitope within the ephrin-binding domain that is closely adjacent to the "low-affinity" ephrin-A5 heterotetramerization site. We show that similar to ephrin-A5, preclustered IIIA4 effectively triggers EphA3 activation, contraction of the cytoskeleton, and cell rounding. BIAcore analysis, immunoblot, and confocal microscopy of wild-type and mutant EphA3 with compromised ephrin-A5 or IIIA4-binding capacities indicate that IIIA4 binding triggers an EphA3 conformation which is permissive for the assembly of EphA3/ephrin-A5-type signaling clusters. Furthermore, unclustered IIIA4 and ephrin-A5 Fc applied in combination initiate greatly enhanced EphA3 signaling. Radiometal conjugates of ephrin-A5 and IIIA4 retain their affinity, and in mouse xenografts localize to, and are internalized rapidly into EphA3-positive, human tumors. These findings show the biological importance of EphA3/ephrin-A5 interactions and that ephrin-A5 and IIIA4 have great potential as tumor targeting reagents.

Pseudoxanthomonas mexicana sp. nov. and Pseudoxanthomonas japonensis sp. nov., isolated from diverse environments, and emended descriptions of the genus Pseudoxanthomonas Finkmann et al. 2000 and of its type species

Three mesophilic bacteria (strains AMX 26BT, UR374_02 and 12-3T) isolated respectively from an anaerobic digester, human urine and urban riverside soil were characterized. Cells were Gram-negative, motile, non-sporulating, straight to curved rods with one polar flagellum and had a strictly respiratory metabolism with O2 as the preferential terminal electron acceptor. Phylogenetic analysis based on 16S rRNA gene sequences revealed that all strains clustered within the Xanthomonadaceae branch of the Proteobacteria. Isolates AMX 26BT and UR374_02 exhibited 100 % 16S rRNA gene sequence similarity and both were related to strain 12-3T (99·6 % similarity). The closest relative of all the isolates was Pseudoxanthomonas broegbernensis DSM 12573T (similarity 97·1–97·5 %), and they were equidistantly related to Xanthomonas species (95·4–96·6 %), Stenotrophomonas species (95·3–96·1 %) and Pseudoxanthomonas taiwanensis ATCC BAA-4040T (95·3–95·4 %). Chemotaxonomic and biochemical data (branched-chain cellular fatty acid pattern without C13 : 0 iso 3-OH, ubiquinone with eight isoprenoid units, limited range of substrates used, ability to reduce nitrite but not nitrate with the production of N2O) supported their affiliation to the genus Pseudoxanthomonas. The results of DNA–DNA hybridization and/or phenotypic analysis allowed them to be differentiated from the two Pseudoxanthomonas species with validly published names and showed that strain 12-3T was genomically and phenotypically distinct from the other two isolates. On the basis of these results, two novel species of the genus Pseudoxanthomonas are proposed: Pseudoxanthomonas mexicana sp. nov., consisting of strains AMX 26BT (=ATCC 700993T=CIP 106674T=JCM 11524T) (type strain) and UR374_02 (=DSM 15133), and Pseudoxanthomonas japonensis sp. nov., consisting of strain 12-3T (=CCUG 48231T=CIP 107388T=JCM 11525T). The report of these two novel species leads to the emendation of the description of the genus Pseudoxanthomonas and the re-evaluation of the phenotype of P. broegbernensis DSM 12573T necessitates the emendation of its description.