Host preferences of two encyrtid parasitoids for the Columbian Phenacoccus spp. of cassava mealybugs

In a choice test among six life stages of Phenacoccus herreni Cox & Williams, Epidinocarsis diversicornis (Howard) used its antennae to examine adult and 3rd stadium females more than other stages and preferentially attempted to oviposit in these plus 2nd stadium females. Success of ovipositor insertion was unaffected by host stage. The outcome of these behaviors was preferential oviposition by E. diversicornis in the large female host stages. Acerophagus coccois Smith also preferentially examined larger female mealybugs (second and third stadium nymphs and adults) more than other stages and successfully inserted its ovipositor in these stages more often than in second stadium male nymphs and male cocoons, resulting in a similar preference in this species for larger female host stages. When given a choice between adult female hosts of two species, P. herreni and Phenacoccus gossypii Townsend & Cockerell, E. diversicornis exhibited a clear preference for P. herreni; whereas A. coccois preferred P. gossypii.

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Résumé Epidinocarsis diversicornis (Howard), ayant la possibilité de choisir entre six stades différents de Phenacoccus herreni Cox & Williams, examine avec ses antennes plus particulièrement les adultes et les larves femelles du 3ème stade, et essaie de pondre de préférence dans ces stades et les larves femelles de second stade. L'insertion de la tarière s'effectue aussi bien quel que soit le stade de l'hôte. Il résulte de ces différents aspects du comportement que E. diversicornis pond de préférence dans les femelles des stades les plus avancés. Acerophagus coccois Smith préfère aussi examiner les cochenilles femelles les plus grosses (second et 3ème stade larvaires et adulte), et introduit sa tarière avec succès dans ces stades plus souvent que dans les larves mâles de second stade ou les cocons mâles; il en résulte aussi pour cette espèce une préférence pour les femelles des stades les plus gros.Quand on leur a donné le choix entre des femelles des deux espèces de cochenilles (P. herreni et Phenacoccus gossypii Towsend & Cockerell), E. diversicornis manifestait une nette préférence pour P. herreni, tandis que A. coccois préférait P. gossypii.

     

Amino acid sequence of k Sci, the Bence Jones protein isolated from a patient with light chain deposition disease

Light chain Sci was isolated from the urine of a patient affected by light chain deposition disease with an apparent exclusive localization to the kidney. Sci protein is an intact light chain: it consists of 214 amino acid residues and has an Mr of 23.65. Its complete primary structure has been determined by sequence analysis of the corresponding tryptic peptides and by partially sequencing the intact protein. Sequence comparison shows that Sci protein is strictly related to the light chains of kIIIa family (88% structural identity) which are usually expressed in autoimmune rheumatoid syndromes. Computer graphics model suggests a perturbation in k Sci three-dimensional structure due to the unusual replacement of residues 53 and 77.     

Fascioloides magna (Bassi, 1875) in feral swine from southern Texas.

Between 1971 and 1975, Fascioloides magna was found in 46 of 67 (69%) feral swine (Sus scrofa) in southern Texas. Flukes were recovered from swine in areas where F. magna commonly has been recovered from white-tailed deer and cattle. One to 12 flukes were recovered from each infected animal. Their presence was indicated by black hematin pigment on the liver and various other internal organs. Eggs were not detected in the gallbladder or feces of infected animals although mature flukes and eggs were recovered in the livers suggesting that, like cattle, feral swine can be infected but are aberrant hosts for the parasite and do not disseminate eggs.     

Monitoring the Interaction between β2-Microglobulin and the Molecular Chaperone αB-crystallin by NMR and Mass Spectrometry: αB-CRYSTALLIN DISSOCIATES β2-MICROGLOBULIN OLIGOMERS*

The interaction at neutral pH between wild-type and a variant form (R3A) of the amyloid fibril-forming protein β₂-microglobulin (β2m) and the molecular chaperone αB-crystallin was investigated by thioflavin T fluorescence, NMR spectroscopy, and mass spectrometry. Fibril formation of R3Aβ2m was potently prevented by αB-crystallin. αB-crystallin also prevented the unfolding and nonfibrillar aggregation of R3Aβ2m. From analysis of the NMR spectra collected at various R3Aβ2m to αB-crystallin molar subunit ratios, it is concluded that the structured β-sheet core and the apical loops of R3Aβ2m interact in a nonspecific manner with the αB-crystallin. Complementary information was derived from NMR diffusion coefficient measurements of wild-type β2m at a 100-fold concentration excess with respect to αB-crystallin. Mass spectrometry acquired in the native state showed that the onset of wild-type β2m oligomerization was effectively reduced by αB-crystallin. Furthermore, and most importantly, αB-crystallin reversibly dissociated β2m oligomers formed spontaneously in aged samples. These results, coupled with our previous studies, highlight the potent effectiveness of αB-crystallin in preventing β2m aggregation at the various stages of its aggregation pathway. Our findings are highly relevant to the emerging view that molecular chaperone action is intimately involved in the prevention of in vivo amyloid fibril formation.     

Molecular insights into cell toxicity of a novel familial amyloidogenic variant of β2‐microglobulin

The first genetic variant of β₂‐microglobulin (b2M) associated with a familial form of systemic amyloidosis has been recently described. The mutated protein, carrying a substitution of Asp at position 76 with an Asn (D76N b2M), exhibits a strongly enhanced amyloidogenic tendency to aggregate with respect to the wild‐type protein. In this study, we characterized the D76N b2M aggregation path and performed an unprecedented analysis of the biochemical mechanisms underlying aggregate cytotoxicity. We showed that, contrarily to what expected from other amyloid studies, early aggregates of the mutant are not the most toxic species, despite their higher surface hydrophobicity. By modulating ganglioside GM1 content in cell membrane or synthetic lipid bilayers, we confirmed the pivotal role of this lipid as aggregate recruiter favouring their cytotoxicity. We finally observed that the aggregates bind to the cell membrane inducing an alteration of its elasticity (with possible functional unbalance and cytotoxicity) in GM1‐enriched domains only, thus establishing a link between aggregate‐membrane contact and cell damage.     

A partially structured species of beta 2-microglobulin is significantly populated under physiological conditions and involved in fibrillogenesis

The folding of beta(2)-microglobulin (beta(2)-m), the protein forming amyloid deposits in dialysis-related amyloidosis, involves formation of a partially folded conformation named I(2), which slowly converts into the native fold, N. Here we show that the partially folded species I(2) can be separated from N by capillary electrophoresis. Data obtained with this technique and analysis of kinetic data obtained with intrinsic fluorescence indicate that the I(2) conformation is populated to approximately 14 +/- 8% at equilibrium under conditions of pH and temperature close to physiological. In the presence of fibrils extracted from patients, the I(2) conformer has a 5-fold higher propensity to aggregate than N, as indicated by the thioflavine T test and light scattering measurements. A mechanism of aggregation of beta(2)-m in vivo involving the association of the preformed fibrils with the fraction of I(2) existing at equilibrium is proposed from these results. The possibility of isolating and quantifying a partially folded conformer of beta(2)-m involved in the amyloidogenesis process provides new opportunities to monitor hemodialytic procedures aimed at the reduction of such species from the pool of circulating beta(2)-m but also to design new pharmaceutical approaches that consider such species as a putative molecular target.     

Detection of two partially structured species in the folding process of the amyloidogenic protein beta 2-microglobulin

beta 2-Microglobulin is a small, major histocompatibility complex class I-associated protein that undergoes aggregation and accumulates as amyloid deposits in human tissues as a consequence of long-term haemodialysis. The folding process of this amyloidogenic protein has been studied in vitro by diluting the guanidine hydrochloride-denatured protein in refolding buffer at pH 7.4 and monitoring the folding process by means of a number of spectroscopic probes that allow the native structure of the protein to be detected as it develops. These techniques include fluorescence spectroscopy, far and near-UV circular dichroism, 8-anilino-1-naphthalenesulfonic acid binding and double jump assays. All spectroscopic probes indicate that a significant amount of structure forms within the dead-time of stopped-flow measurements (<5 ms). The folding reaction goes to completion through a fast phase followed by a slow phase, whose rate constants are ca 5.1 and 0.0030 s(-1) in water, respectively. Unfolding-folding double jump experiments, together with the use of peptidyl prolyl isomerase, reveal that the slow phase of folding of beta 2-microglobulin is not fundamentally determined by cis/trans isomerisation of X-Pro peptide bonds. Other folding-unfolding double jump experiments also suggest that the fast and slow phases of folding are not related to independent folding of different populations of protein molecules. Rather, we provide evidence for a sequential mechanism of folding where denatured beta 2-microglobulin collapses to an ensemble of partially folded conformations (I(1)) which fold subsequently to a more highly structured species (I(2)) and, finally, attain the native state. The partially folded species I(2) appears to be closely similar to previously studied amyloidogenic forms of beta 2-microglobulin, such as those adopted by the protein at mildly acid pH values and by a variant with six residues deleted at the N terminus. Since amyloid formation in vivo originates from partial denaturation of beta 2-microglobulin under conditions favouring the folding process, the long-lived, partially structured species detected here might be significantly populated under some physiological conditions and hence might play an important role in the process of amyloid formation.     

In field damage of high and low cyanogenic cassava due to a generalist insect herbivore Cyrtomenus bergi (Hemiptera: Cydnidae)

The hypothesis that cyanogenic potential in cassava roots deters polyphagous insects in the field is relevant to current efforts to reduce or eliminate the cyanogenic potential in cassava. To test this hypothesis, experiments were conducted in the field under natural selection pressure of the polyphagous root feeder Cyrtomenus bergi Froeschner (Hemiptera: Cydnidae). A number of cassava varieties (33) as well as 13 cassava siblings and their parental clone, each representing a determined level of cyanogenic potential (CNP), were scored for damage caused by C. bergi and related to CNP and nonglycosidic cyanogens, measured as hydrogen cyanide. Additionally, 161 low-CNP varieties (< 50 ppm hydrogen cyanide, fresh weight) from the cassava germplasm core collection at Centro Internacional de Agricultura Tropical (CIAT) were screened for resistance/tolerance to C. bergi. Low root damage scores were registered at all levels of CNP. Nevertheless, CNP and yield (or root size) partly explained the damage in cassava siblings (r2 = 0.82) and different cassava varieties (r2 = 0.42), but only when mean values of damage scores were used. This relation was only significant in one of two crop cycles. A logistic model describes the underlying negative relation between CNP and damage. An exponential model describes the underlying negative relation between root size and damage. Damage, caused by C. bergi feeding, released nonglycosidic cyanogens, and an exponential model fits the underlying positive relation. Fifteen low-CNP clones were selected for potential resistance/tolerance against C. bergi.     

IL-11 and IL-11Rα immunolocalisation at primate implantation sites supports a role for IL-11 in placentation and fetal development

Embryo implantation, endometrial stromal cell decidualization and formation of a functional placenta are critical processes in the establishment and maintenance of pregnancy. Interleukin (IL)-11 signalling is essential for adequate decidualization in the mouse uterus and IL-11 promotes decidualization in the human. IL-11 action is mediated via binding to the specific IL-11 receptor α (IL-11Rα). The present study examined immunoreactive IL-11 and IL-11Rα in cycling rhesus monkey endometrium, at implantation sites in cynomolgus and rhesus monkeys and in human first trimester decidua and defined distinct spatial and temporal patterns. In cycling rhesus monkey endometrium, IL-11 and IL-11Rα increased in both basalis and functionalis regions during the secretory compared with the proliferative phase, with changing cellular locations in luminal and glandular epithelium and stroma. The patterns were similar overall to those previously described in human endometrium. Differences were seen in immunostaining during implantation in cynomologus and rhesus monkey. In the cynomolgus, very little staining for IL-11 or IL-11Rα was seen in syncytio- and cyto-trophoblast cells in the villi between days 12 and 150 of pregnancy although there was moderate staining in cytotrophoblast in the shell between days 12 and 17 and in subpopulations of cytotrophoblast cells invading the arteries at day 17. By contrast in the rhesus monkey between days 24 and 35 of pregnancy and in human first trimester placenta, cyto- and syncytio-trophoblast in the villi but not cytotrophoblast in the shell were positively stained. The most intense staining for both IL-11 and IL-11Rα was present within the decidua in the maternal component of implantation sites in all three primates but moderate staining was also present in maternal vascular smooth muscle and glands perivascular cells and epithelial plaques. These results are consistent with a role for IL-11 both during decidualization and placentation in primates.