Ecdysteroids in nematodes

The occurrence of ecdysteroids (insect moulting hormones) in nematodes, albeit at low concentrations, has been firmly established. In addition to apparently stimulating moulting in a few species, exogenously applied ecdysteroids have now been shown to have interesting biological effects on meiotic reinitiation in oocytes and on microfilarial production in filariae. Although such effects demonstrate the feasibility of influencing nematode physiology with exogenously applied ecdysteroids, hitherto it has not been possible to demonstrate synthesis de novo of these steroids in nematodes. Thus, it remains to be established whether ecdysteroids are truly endogenous nematode hormones or merely represent compounds with strong biological activity. Nonetheless, there are indications that interference with the ecdysteroid system might be exploitable in the development of novel approaches to control of nematodes.     

P-glycoproteins in nematodes

The P-glycoprotein (Pgp), a member of a group of integral membrane proteins that contain the ATP-binding cassette, is widely represented in the animal kingdom. A family of Pgp homologues has recently been described in nematodes. Pgps have been implicated in drug resistance in Plasmodium and in other parasitic protozoa, so the interest of porasitologists now focuses on whether or not they are involved in anthelmintic resistance. Their role in normal cellular functions is also discussed in this article by Nick Songster.     

Sex attractants in nematodes

Nematodes communicate with each other using pheromones - chemicals secreted by one individual that affect the behaviour of others of the same species. Chemicals secreted into the environment are known to influence host location, dormancy (dauer-larva formation), competitive interactions and mate detection; they benefit the nematode by reducing energy expenditure on less orientated movements. Of these chemicals, sex pheromones associated with mate detection and attraction are of particular interest as potential biological control agents. Here, Barbara MacKinnon discusses these developments.     

Cold tolerance in nematodes

Summary The nematodesTrichostrongylus colubriformis (J3),Ditylenchus dipsaci (J4) andPanagrellus silusae (adults) are freezing-susceptible but can avoid freezing by supercooling. Their mean supercooling points were –30.0±0.7°C forT. colubriformis, –21.7±0.7°C forD. dipsaci and –20.7±0.84°C forP. silusae. T. colubriformis andD. dipsaci could prevent seeding by external ice butP. silusae could not. The glycerol concentrations of these nematodes are considered to be too low to have a significant antifreeze effect.Abbreviations J3 3rd-stage juvenile - J4 4th stage juvenile - SEM standard error of the mean - T ₅₀ 50% survival temperature     

Chromatin diminution in nematodes

The process of chromatin diminution in Parascaris and Ascaris is a developmentally controlled genome rearrangement, which results in quantitative and qualitative differences in DNA content between germ line and somatic cells. Chromatin diminution involves chromosomal breakage, new telomere formation and DNA degradation. The programmed elimination of chromatin in presomatic cells might serve as an alternative way of gene regulation. We put forward a new hypothesis of how an ancient partial genome duplication and chromatin diminution may have served to maintain the genetic balance in somatic cells and simultaneously endowed the germ line cells with a selective advantage.     

Root-knot nematodes

Conclusions The quantity ofMeloidogyne hapla produced on plants depends on the amount of inoculum, the amount of plant present at the moment of root invasion, the plant family, genus, species and variety. Temperature is also a governing factor but this item was not tested in the present experiments. The effect of the nematodes on the host is likewise a complicated interaction.Formerly Division of Nematology, Bureau of Plant Industry, Soils and Agric. Eng.     

Bombesin-like neuropeptides in nematodes.

This paper reports evidence of members of the bombesin-like peptide family in a number of nematodes, including Caenorhabditis, Panagrellus, Dirofilaria, Onchocerca, Brugia, Haemonchus, Ostertagia, Toxocara, and Ascaris. One of these (Ostertagia) secretes the bombesin-like material into its environment. Specific binding of gastrin-releasing peptide to the hypodermis consistent with the presence of receptors was demonstrated. These data suggest that this class of peptides may play an important role in nematode hypodermal physiology.     

Superoxide dismutase activity in nematodes

The activities of the enzymes superoxide dismutase (E.C.:1.15.1.1) and catalase (E.C.:1.11.1.6) were studied in purified extracts of four nematodes: Ascaris suum, Toxascaris leonina, Toxocara canis and T. cati adult males and females. No catalase activity was found in any of the extracts. The results reveal that the SOD activities of the four parasites presented species differences and also sexual differences within each species. Polyacrylamide gel electrophoresis pattern analysis confirmed that the mobilities, widths and band intensities varied according to the species and sex of the parasite from which the enzyme was obtained.     

The FLP-side of nematodes

The central role of FMRFamide-like peptides (FLPs) in nematode motor and sensory capabilities makes FLP signalling an appealing target for new parasiticides. Accumulating evidence has revealed an astounding level of FLP sequence conservation and diversity in the phylum Nematoda, and preliminary work has begun to identify the nematode FLP receptor complement in Caenorhabditis elegans, with a view to investigating their basic biology and therapeutic potential. However, much work is needed to clarify the functional aspects of FLP signalling and how these peptides exert their effects at the organismal level. Here, we summarize our current knowledge of nematode FLP signalling.