The effect of ethoxyzolamide, an analogue of insect juvenile hormone, nor-adrenaline and iodine on changes in the optical path difference in the excretory cells and oesophagus during exsheathment in Haemonchus contortus

Heat shock, but not temperature, is a biological trigger for the exsheathment of third-stage larvae of Haemonchus contortus

Gastrointestinal parasites are an important health issue in grazing ruminants. Understanding the processes involved in the transition from the free living to the parasitic life stage of these nematodes is one avenue to identifying new targets amenable to future intervention. The transition to parasitism is initiated by exsheathment and is triggered by the sudden change in environment after ingestion of the infective larva by the host. Two major changes in environment are the increases in temperature and carbon dioxide (CO₂) levels. For CO₂ a role in exsheathment has been described previously, but the exact role of temperature was unclear. The current study is the first to investigate the importance of temperature in triggering exsheathment of Haemonchus contortus. Carbon dioxide induced exsheathment in H. contortus proved to be temperature dependent, as no exsheathment was observed at room temperatures. However, the temperature requirement to trigger exsheathment was quite specific. A rapid change in temperature (heat shock) very efficiently induced high levels of exsheathment. In contrast, when the larvae were exposed to a slow increase in temperature, the exsheathment response was smaller and delayed. Further investigation revealed that timing of the heat shock in relation to the CO₂ administration was crucial, as well as the final temperature and magnitude of the heat shock. In conclusion, these data indicate that heat shock rather than temperature itself is a crucial aspect in triggering the biological exsheathment cascade, and thus infection process, of H. contortus.

Understanding Haemonchus contortus Better Through Genomics and Transcriptomics

Parasitic roundworms (nematodes) cause substantial mortality and morbidity in animals globally. The barber's pole worm, Haemonchus contortus, is one of the most economically significant parasitic nematodes of small ruminants worldwide. Although this and related nematodes can be controlled relatively well using anthelmintics, resistance against most drugs in common use has become a major problem. Until recently, almost nothing was known about the molecular biology of H. contortus on a global scale. This chapter gives a brief background on H. contortus and haemonchosis, immune responses, vaccine research, chemotherapeutics and current problems associated with drug resistance. It also describes progress in transcriptomics before the availability of H. contortus genomes and the challenges associated with such work. It then reviews major progress on the two draft genomes and developmental transcriptomes of H. contortus, and summarizes their implications for the molecular biology of this worm in both the free-living and the parasitic stages of its life cycle. The chapter concludes by considering how genomics and transcriptomics can accelerate research on Haemonchus and related parasites, and can enable the development of new interventions against haemonchosis.

Gas sensing in nematodes

Nearly all animals are capable of sensing changes in environmental oxygen (O2) and carbon dioxide (CO2) levels, which can signal the presence of food, pathogens, conspecifics, predators, or hosts. The free-living nematode Caenorhabditis elegans is a powerful model system for the study of gas sensing. C. elegans detects changes in O2 and CO2 levels and integrates information about ambient gas levels with other internal and external cues to generate context-appropriate behavioral responses. Due to its small nervous system and amenability to genetic and genomic analyses, the functional properties of its gas-sensing microcircuits can be dissected with single-cell resolution, and signaling molecules and natural genetic variations that modulate gas responses can be identified. Here, we discuss the neural basis of gas sensing in C. elegans, and highlight changes in gas-evoked behaviors in the context of other sensory cues and natural genetic variations. We also discuss gas sensing in other free-living nematodes and parasitic nematodes, focusing on how gas-sensing behavior has evolved to mediate species-specific behavioral requirements.

Differences in transcription between free-living and CO2-activated third-stage larvae of Haemonchus contortus

BACKGROUND

The disease caused by Haemonchus contortus, a blood-feeding nematode of small ruminants, is of major economic importance worldwide. The infective third-stage larva (L3) of this gastric nematode is enclosed in a cuticle (sheath) and, once ingested with herbage by the host, undergoes an exsheathment process that marks the transition from the free-living (L3) to the parasitic (xL3) stage. This study explored changes in gene transcription associated with this transition and predicted, based on comparative analysis, functional roles for key transcripts in the metabolic pathways linked to larval development.

RESULTS

Totals of 101,305 (L3) and 105,553 (xL3) expressed sequence tags (ESTs) were determined using 454 sequencing technology, and then assembled and annotated; the most abundant transcripts encoded transthyretin-like, calcium-binding EF-hand, NAD(P)-binding and nucleotide-binding proteins as well as homologues of Ancylostoma-secreted proteins (ASPs). Using an in silico-subtractive analysis, 560 and 685 sequences were shown to be uniquely represented in the L3 and xL3 stages, respectively; the transcripts encoded ribosomal proteins, collagens and elongation factors (in L3), and mainly peptidases and other enzymes of amino acid catabolism (in xL3). Caenorhabditis elegans orthologues of transcripts that were uniquely transcribed in each L3 and xL3 were predicted to interact with a total of 535 other genes, all of which were involved in embryonic development.

CONCLUSION

The present study indicated that some key transcriptional alterations taking place during the transition from the L3 to the xL3 stage of H. contortus involve genes predicted to be linked to the development of neuronal tissue (L3 and xL3), formation of the cuticle (L3) and digestion of host haemoglobin (xL3). Future efforts using next-generation sequencing and bioinformatic technologies should provide the efficiency and depth of coverage required for the determination of the complete transcriptomes of different developmental stages and/or tissues of H. contortus as well as the genome of this important parasitic nematode. Such advances should lead to a significantly improved understanding of the molecular biology of H. contortus and, from an applied perspective, to novel methods of intervention.

External pH influences the transcriptional profile of the carbonic anhydrase, CAH-4b in Caenorhabditis elegans

Insight into how organisms adapt to environmental stimuli has become increasingly important in recent years for identifying key virulence factors in many species. The life cycle of many pathogenic nematode species forces the organism to experience environments which would otherwise be considered stressful. One of the conditions often encountered by nematodes is a change in environmental pH. Living in a soil environment Caenorhabditis elegans will naturally encounter fluctuations in external pH. Therefore, C. elegans has the potential to provide an insight into how pathogenic nematodes survive and proliferate in these environments. We found that C. elegans can maintain over 90% survival in pH conditions ranging from pH 3 to 10. This was unrelated to the non-specific protection provided by the cuticle. Global transcriptional analysis identified many genes, which were differentially regulated by pH. The gene cah-4 encodes two putative alpha carbonic anhydrases (CAH-4a and CAH-4b), one of which was five-fold up regulated in an alkaline environment (CAH-4b). Stopped-flow analysis of CAH-4b using 35 different carbonic anhydrase inhibitors identified complex benzenesulfonamide compounds as the most potent inhibitors (K(i) 35-89nM).

From insect ovaries to sheep red blood cells: a tale of two hormones

This printed version of the Wigglesworth Lecture reviews the evidence that juvenile hormone (JH) acts on the follicular epithelium of the ovary through a membrane receptor to control access of yolk proteins to the oocyte surface. The thyroid hormones mimic this action through the same receptor. Conversely, both JH III and 3,5,3' triiodothyronine (T3) increase the activity of Ca ATPase in isolated erythrocyte membrane preparations from sheep, apparently through the same membrane receptor. These effects are mimicked by exposure of the respective tissues to CO(2). These findings suggest that the hormones arose as biotic signals, originally using existing CO(2) receptors.

The effect of catecholamines and catecholamine antagonists on the third larval moult of Dirofilaria immitis in vitro

Various catecholamines and catecholamine antagonists have been examined for their effects on the third larval moult of the parasitic nematode. Dirofilaria immitis, cultured in vitro. The non-selective alpha and beta agonist, noradrenaline, and the beta agonist, isoprenaline, had no effect on the timing of the third stage moult when used at a concentration of 10(-5) M. The alpha-adrenergic antagonist, phentolamine, resulted in worm mortality at 10(-5) M. At 10(-7) M, both phentolamine and the beta-antagonist, propranolol caused a significant reduction in the numbers of larvae capable of completing the third stage moult. Idazoxan, an alpha 2-antagonist, at 10(-5) M did not affect worm mortality but did completely prevent ecdysis. The potential of these compounds as possible filaricides is discussed.

Ultrastructural changes associated with exsheathment of infective juveniles of Haemonchus contortus

Ultrastructural changes associated with exsheathment of the infective juveniles of Haemonchus contortus are described. Hyaline ring formation occurs associated with annulations 10 and 20 and consists of the dissolution of the basal zone and the inner electron-dense layer resulting in the rupture of the sheath. These changes are consistent with the action of a protease-exsheathing enzyme. There is a significant reduction associated with exsheathment in the size of the excretory cells and the number of excretory granules contained within them. No changes in the oesophagus were observed associated with exsheathment. These, and the observations of earlier workers, suggest that it is the excretory cells and not the oesophagus which are the source of exsheathing fluid during exsheathment.