Toxins produced by arthropod parasites: salivary gland proteins of human body lice and venom proteins of chelonine wasps.

A review is presented of our ongoing research projects on the protein components of the saliva of human body lice and of the non-paralyzing venom of wasps in the subfamily Cheloninae. Sodium dodecyl sulfate-polyacryamide gel electrophoretic analysis of lice salivary gland proteins showed a predominance of high and intermediate mol. wt proteins. Immunoblotting with a low titer polyclonal antiserum to lice salivary proteins indicated that some, but not all, of the predominant high mol. wt salivary gland proteins are injected into the host during feeding. The venom of a Chelonus sp. wasp contains a chitinase, and a 33,000 mol. wt protein with a primary structure composed mostly of a series of 12 tandem repeats of a 14-residue sequence. The N-terminus of this protein and its homologs in a related species of Ascogaster share a conserved adjacent pair of acidic residues. Epitope mapping/immunoprecipitation experiments now in progress will provide information on which linear motifs are on the surface of the protein, and will thereby provide information on the tertiary structure of the protein.

Overview of the regulation of metamorphosis-associated genes in Trichoplusia ni.

A review is presented of our ongoing research program on the regulation of metamorphosis-associated proteins in Trichoplusia ni. Toward the identification of mechanisms by which juvenile hormone (JH) regulates expression of metamorphosis-associated proteins, we have identified a protein that is induced by JH (juvenile hormone esterase) and a related esterase that is not JH-inducible. We have also identified three hexamerins that are suppressible by JH, and one hexamerin that is not JH-suppressible. Expression of the hexamerins is regulated at the transcriptional, translational, and posttranslational levels in T. ni. The rate of transcription of the JH esterase gene increases at the time of the prepupal peak in JH, and exogenous application of JH can cause, within 3 h, the rate of transcription to be the markedly elevated above normal. Using in vitro functional transcription assay, cell line transfection functional assay, and preliminary DNase I hypersensitive site mapping we were able to identify the functional TATA box and transcription start sites of JH-sensitive genes. These methods were also observed to be powerful in the detection of regulatory DNA motifs involved in the modulation of transcriptional activity constitutively imparted by a core promoter. The experimental systems described here will also be effective in identifying those components through which JH regulatory effects are mediated. Should JH act on the genes in a primary manner, then the transcription factor mediating that action may be the (a) JH receptor. Should the JH action be in a secondary manner, then the transcription factor(s) whose activity at the JHE gene is regulated by JH will provide the tool to track back to the location and nature of the primary JH action.

Altered hexamerin regulation in prepupal Trichoplusia ni pseudoparasitized by Chelonus sp. near curvimaculatus.

Adult female wasps of species in the subfamily Cheloninae inject an egg, venom, polydnavirus and other materials into the host egg during oviposition. Hosts then exhibit precocious expression of the metamorphic developmental program, but then further development by the precocious prepupa is suppressed. These effects occur in truly parasitized hosts (those that contain a live endoparasite larva) as well as in pseudoparasitized hosts (that do not contain a live endoparasite). We report here that during the precocious prepupal stage, the hexamerins BJHSP1 and BJHSP2 persist in the hemolymph of pseudoparasitized hosts, whereas in normal larvae these proteins are cleared from the hemolymph in response to the normal surge in prepupal ecdysteroids. Northern blot analysis of poly(A) RNA showed that the basis for this persistence is not an abnormally high abundance of the transcripts on the day following wandering in pseudoparasitized larvae. Nor is the source of the hexamerins the parasite larva, for it is missing from the pseudoparasitized hosts. The hypothesis that the persistence is due to a suppressed titer of ecdysteroids in pseudoparasitized hosts (reported earlier: [jones et al., Arch Insect Biochem Physiol 21:155 (1992)] was tested by use of a large size variant of pseudoparasitized hosts in which the prepupal ecdysteroid titer is partially restored by endogenous ecdysteroid production. In such pseudoparasitized prepupae, the two hexamerins were cleared from the hemolymph on the day following host wandering behavior, as in normal larvae. Thus, the regulatory basis of the persistence of the hexamerins BJHSP1 and BJHSP2 in the hemolymph of pseudoparasitized hosts appears to be at the posttranslational level, with suppression of the prepupal ecdysteroid titer causing omission of the normal trigger for fat body uptake of the hexamerins.