Ascaris suum: free amino acids and proteins in the pseudocoelom, seminal vesicle, and glandular vas deferens

Ascaris suum Nutrient Uptake and Metabolic Release, and Modulation of Host Intestinal Nutrient Transport by Excretory-Secretory and Cuticle Antigens In Vitro

Ascaris suum, the most important pig parasite, also infects humans as a zoonotic pathogen. Malabsorption upon infection probably results from impaired nutrient transport, presumably mediated by the parasite’s excretory-secretory (ES) or cuticle somatic (CSO) antigens. The present study investigated the electrogenic transport (ΔI_sc) of glucose, alanine and the dipeptide glycyl-l-glutamine (glygln), as well as glucose net flux rates in pig jejunal tissue after in vitro exposure to adult A. suum total ES or CSO antigens in Ussing chambers. ΔI_sc of glucose, alanine and glucose net flux rate were significantly decreased after one hour of exposure to total ES antigen. In contrast, CSO antigens increased the transport of glygln. Additionally, nutrient uptake and ES antigen pattern were compared in culture medium from untreated adult worms and those with sealed mouth and anal openings. Untreated worms completely absorbed glucose, while cuticular absorption in sealed worms led to 90% reduction. Amino acid absorption was 30% less effective in sealed worms, and ammonia excretion decreased by 20%. Overall, the results show that A. suum total ES antigen rapidly impairs nutrient transport in vitro. Future studies confirming the results in vivo, narrowing down the ES components responsible and investigating underlying molecular mechanisms are needed.

SNF-10 connects male-derived signals to the onset of sperm motility in C. elegans

Sperm from the nematode C. elegans gain motility during a process termed activation, which they initiate in response to specific environmental signals. During this process, a number of subcellular rearrangements occur, culminating in an altered morphology that allows the cell to crawl toward and fertilize oocytes. Both hermaphrodites and males produce sperm, and redundant, sex-biased pathways regulate the sperm's activation. The male-derived signal for sperm activation involves TRY-5, a trypsin-like serine protease in seminal fluid, but until recently it was unknown what factors were active downstream of TRY-5. In our recent paper, we reported the discovery of SNF-10, a solute carrier 6 (SLC6) family protein that is expressed by sperm and connects the activation signal to changes in sperm morphology and, ultimately, the onset of motility. Here, we review our recent results, focusing on potential models for SNF-10's function in C. elegans, and additionally discuss the role SLC6 transporters may play in male reproductive biology from invertebrates to mammals.

Cytosolic Ca(2+) as a multifunctional modulator is required for spermiogenesis in Ascaris suum

The dynamic polar polymers actin filaments and microtubules are usually employed to provide the structural basis for establishing cell polarity in most eukaryotic cells. Radially round and immotile spermatids from nematodes contain almost no actin or tubulin, but still have the ability to break symmetry to extend a pseudopod and initiate the acquisition of motility powered by the dynamics of cytoskeleton composed of major sperm protein (MSP) during spermiogenesis (sperm activation). However, the signal transduction mechanism of nematode sperm activation and motility acquisition remains poorly understood. Here we show that Ca(2+) oscillations induced by the Ca(2+) release from intracellular Ca(2+) store through inositol (1,4,5)-trisphosphate receptor are required for Ascaris suum sperm activation. The chelation of cytosolic Ca(2+) suppresses the generation of a functional pseudopod, and this suppression can be relieved by introducing exogenous Ca(2+) into sperm cells. Ca(2+) promotes MSP-based sperm motility by increasing mitochondrial membrane potential and thus the energy supply required for MSP cytoskeleton assembly. On the other hand, Ca(2+) promotes MSP disassembly by activating Ca(2+)/calmodulin-dependent serine/threonine protein phosphatase calcineurin. In addition, Ca(2+)/camodulin activity is required for the fusion of sperm-specifi c membranous organelle with the plasma membrane, a regulated exocytosis required for sperm motility. Thus, Ca(2+) plays multifunctional roles during sperm activation in Ascaris suum.

Amino acid metabolism in helminths

Amino acids are major constituents of biological material. Chemically they are extremely stable and combine a relatively simple molecular structure with a wide range of properties and functions. In general, amino acid metabolism in helminths has been relatively neglected and the information available is often uneven and of uncertain quality. However, the search for new target sites for anthelmintic development has led to a renewed interest in this area. The amino acid composition of helminths is similar to that of other invertebrates and no unique amino acids have been reported. With the possible addition of tyrosine, helminths seem to require the same 10 essential amino acids as mammals and, where studied in detail, the pathways of amino acid synthesis in helminths are similar to those of mammals. Although amino acids are not a significant energy source in parasites, helminths are able to catabolize amino acids by pathways which, again, appear identical to those found in mammals. Helminths have also been shown to carry out a number of oxidative reactions associated with amino acid metabolism, including cysteine dioxygenase, proline hydroxylase and tryptophan hydroxylase. There are, however, differences in detail between the pathways of amino acid metabolism in helminths and mammals, particularly in the metabolism of the sulphur amino acids and arginine and proline. These differences may be exploitable in anthelmintic design and proline analogues and proline biosynthesis inhibitors show some potential as fasciolicides (Sheers et al., 1982). Differences in metabolism between parasites and their hosts may be the result of parasitic adaptation or they may merely reflect general features of the invertebrate phyla as a whole. Thus a comparison of amino acid metabolism in parasitic helminths with that of their free-living relatives may give some insight into the biochemical basis of parasitism.

Amino acid biosynthesis in Haemonchus contortus from C14-labelled precursors, in vitro

Adult Haemonchus contortus (Nematoda: Trichostrongylidae) was investigated for its ability to utilize various C14-labelled precursors, i.e., glucose, acetate, CO2 and palmitic acid, for amino acid biosynthesis. H. contortus has been demonstrated to be capable of synthesizing essential as well as non-essential amino acids. Label from all the precursors was detected in aspartic acid, lysine, histidine, cystine, cysteine, glutamic acid, proline, arginine, tyrosine, alanine, glycine, serine, valine, methionine, leucine and isoleucine. Glutamic acid, aspartic acid, alanine, glycine and serine were synthesized to a greater extent relative to the other amino acids, regardless of the precursor employed. However, in case of glucose, there was comparatively less incorporation into glycine and serine. Incorporation of C14 into various amino acids is evidence for the operation of tricarboxylic acid cycle. Further, the fact that carbon from palmitic acid appears in amino acids, indicates that adult H. contortus is capable of catabolizing long-chain fatty acids. Possible mechanisms for the involvement of various precursors in amino acids biosynthesis are examined here.

[A Comparative Analysis Of Various Parts Of Ascaris Suum With Respect To Their Protein Composition]

For the purpose of making a comparative study of protein compositions in Ascaris suum by sexes and body parts, extracts were prepared from whole bodies, body walls, genital organs, digestive organs and body fluid, of both sexes. And electrophoretic analysis was conducted using polyacrylamide slab gel in the presence of sodium dodecyl sulfate. The results were as follows: 1. In this study, protein bands of each part were separated in the largest number and most clearly under 8%~12 % (10 %) gradient gel condition. The number of bands by body parts was 43 in body walls, 51 in genital organs, 47 in digestive organs, and 34 in body fluid. 2. When examined in terms of sex, the number of bands of whole body was 38 in females and 35 in males. 3. The electrophoretic patterns of body wall protein were in most cases similar with those seen in digestive organs. And the band with a molecular weight of 72,900 was unique to the body wall, and the 122,000 MW band was unique to the female body wall. 4. In genital organ extracts, large molecular weight proteins (more than 80,000) were more frequently met. The molecular weights showed some differences between the two sexes. Of the bands, those having molecular weights of 119,700, 100,500, 88,500 and 86,100 were unique to the female genital organs. On the other hand, the male genital organs showed unique bands having molecular weights of 87,100, 82,800, and 15,500. An unique band common to the genital organs of both sexes was one having 49,300 MW. 5. In the digestive organs evenly distributed protein bands of molecular weights of l0,000~120,000 were observed. The band having 59,800 MW was unique to the digestive organs. The number of bands obtained from body fluid was comparatively small, and the number of bands having less than 30,000 MW was 7, accounting for 55 % of the total protein amounts. The bands having 47,600 MW and 31,400 MW were unique to body fluid.