MicroRNAs (miRNAs) can regulate nearly all biological processes and their dysregulation is implicated in various complex diseases and pathological conditions. Recent years have seen a growing number of functional studies of miRNAs using high-throughput experimental technologies, which have produced a large amount of high-quality data regarding miRNA target genes and their interactions with small molecules, long non-coding RNAs, epigenetic modifiers, disease associations, etc. These rich sets of information have enabled the creation of comprehensive networks linking miRNAs with various biologically important entities to shed light on their collective functions and regulatory mechanisms. Here, we introduce miRNet, an easy-to-use web-based tool that offers statistical, visual and network-based approaches to help researchers understand miRNAs functions and regulatory mechanisms. The key features of miRNet include: (i) a comprehensive knowledge base integrating high-quality miRNA-target interaction data from 11 databases; (ii) support for differential expression analysis of data from microarray, RNA-seq and quantitative PCR; (iii) implementation of a flexible interface for data filtering, refinement and customization during network creation; (iv) a powerful fully featured network visualization system coupled with enrichment analysis. miRNet offers a comprehensive tool suite to enable statistical analysis and functional interpretation of various data generated from current miRNA studies. miRNet is freely available at http://www.mirnet.ca.

Serotonin is an important neuroactive substance in all the parasitic helminths. In Schistosoma mansoni, serotonin is strongly myoexcitatory; it potentiates contraction of the body wall muscles and stimulates motor activity. This is considered to be a critical mechanism of motor control in the parasite, but the mode of action of serotonin is poorly understood. Here we provide the first molecular evidence of a functional serotonin receptor (Sm5HTR) in S. mansoni. The schistosome receptor belongs to the G protein-coupled receptor (GPCR) superfamily and is distantly related to serotonergic type 7 (5HT7) receptors from other species. Functional expression studies in transfected HEK 293 cells showed that Sm5HTR is a specific serotonin receptor and it signals through an increase in intracellular cAMP, consistent with a 5HT7 signaling mechanism. Immunolocalization studies with a specific anti-Sm5HTR antibody revealed that the receptor is abundantly distributed in the worm's nervous system, including the cerebral ganglia and main nerve cords of the central nervous system and the peripheral innervation of the body wall muscles and tegument. RNA interference (RNAi) was performed both in schistosomulae and adult worms to test whether the receptor is required for parasite motility. The RNAi-suppressed adults and larvae were markedly hypoactive compared to the corresponding controls and they were also resistant to exogenous serotonin treatment. These results show that Sm5HTR is at least one of the receptors responsible for the motor effects of serotonin in S. mansoni. The fact that Sm5HTR is expressed in nerve tissue further suggests that serotonin stimulates movement via this receptor by modulating neuronal output to the musculature. Together, the evidence identifies Sm5HTR as an important neuronal protein and a key component of the motor control apparatus in S. mansoni.

Exosomes are small vesicles of endocytic origin, which are released into the extracellular environment and mediate a variety of physiological and pathological conditions. Here we show that Schistosoma mansoni releases exosome-like vesicles in vitro. Vesicles were purified from culture medium by sucrose gradient fractionation and fractions containing vesicles verified by western blot analyses and electron microscopy. Proteomic analyses of exosomal contents unveiled 130 schistosome proteins. Among these proteins are common exosomal markers such as heat shock proteins, energy-generating enzymes, cytoskeletal proteins, and others. In addition, the schistosome extracellular vesicles contain proteins of potential importance for host-parasite interaction, notably peptidases, signaling proteins, cell adhesion proteins (e.g., integrins) and previously described vaccine candidates, including glutathione-S-transferase (GST), tetraspanin (TSP-2) and calpain. S. mansoni exosomes also contain 143 microRNAs (miRNA), of which 25 are present at high levels, including miRNAs detected in sera of infected hosts. Quantitative PCR analysis confirmed the presence of schistosome-derived miRNAs in exosomes purified from infected mouse sera. The results provide evidence of vesicle-mediated secretion in these parasites and suggest that schistosome-derived exosomes could play important roles in host-parasite interactions and could be a useful tool in the development of vaccines and therapeutics.

The flatworm nervous system employs a wide repertoire of neuroactive substances, including small chemical messengers, the so called classical transmitters, and several types of neuropeptides. A large body of research accumulated over four decades has provided a wealth of information on the tissue localization and effects of these substances, their biochemistry and, recently, their molecular modes of action in all major classes of flatworms. This evidence will be reviewed, with particular emphasis on the small (classical) transmitters and the receptors that mediate their effects. One of the themes that will emerge from this discussion is that classical transmitters regulate core activities such as movement, metabolism and transport, and thus are essential for survival of the organism. In addition, the evidence shows that flatworms have multiple neurotransmitter receptors, many with unusual pharmacological features, which make them particularly attractive as drug targets. Understanding the molecular basis of these distinctive properties, and developing new, more specific receptor agonists and antagonists will undoubtedly become a major challenge in future research.

Serotonin [5-hydroxytryptamine (5-HT)] modulates feeding activity, egg-laying, and mating behavior in the free-living nematode, Caenorhabditis elegans. We have cloned a novel receptor cDNA from C. elegans (5-HT 2Ce ) that has high sequence homology with 5-HT 2 receptors from other species. When transiently expressed in COS-7 cells, 5-HT 2Ce exhibited 5-HT binding activity and activated Ca 2ϩ -mediated signaling in a manner analogous to other 5-HT 2 receptors. However, 5-HT 2Ce displayed unusual pharmacological properties, which resembled both 5-HT 2 and 5-HT 1 -like receptors but did not correlate well with any of the known 5-HT 2 subtypes. Two splice variants of 5-HT 2Ce that differ by 48 N-terminal amino acids were identified. The two isoforms were found to have virtually identical binding and signaling properties but differed in their levels of mRNA expression, with the longer variant being four times more abundant than the shorter species in all developmental stages tested. Taken together, the results describe two variants of a novel C. elegans 5-HT receptor, which has some of the properties of the 5-HT 2 family but whose pharmacological profile does not conform to any known class of receptor. Key Words: Caenorhabditis elegans-Serotonin-5-HT 2 receptor-G protein-coupled receptorCloning-Expression-Spliced leader-Aequorin. J. Neurochem. 72, 1372Neurochem. 72, -1383Neurochem. 72, (1999.Serotonin [5-hydroxytryptamine (5-HT)] is a widely distributed neuroactive agent of vertebrates and invertebrates. In the free-living nematode Caenorhabditis elegans, 5-HT has been identified within several central and peripheral neurons, including the well-characterized pharyngeal neurosecretory motorneurons, the hermaphrodite-specific neurons, and the male-specific CP neurons (Horvitz et al., 1982;Desai et al., 1988;Loer and Kenyon, 1993). The serotonergic neurosecretory motor neurons may modulate pharyngeal pumping (feeding), locomotion, and egg laying, whereas the hermaphroditespecific neurons and CP neurons seem to affect egglaying and male mating behavior, respectively (Horvitz et al., 1982;Desai and Horvitz, 1989;Loer and Kenyon, 1993). These effects of 5-HT are mediated, in part, by G proteins (Bargmann and Kaplan, 1998) and at least one type of G protein-coupled receptor (GPCR), which is negatively linked to adenylate cyclase (Olde and McCombie, 1997). It is unknown at present if there are other receptors and pathways of signal transduction that mediate the multiple effects of 5-HT in this animal.In mammals, where 5-HT is a well-established neurotransmitter involved in a wide range of physiological activities (Leonard, 1994), as many as seven different classes of 5-HT receptors (5-HT 1 -5-HT 7 ) have been identified, all of which are further divided into multiple subtypes (Hoyer et al., 1994;Gerhardt and Van Heerikhuizen, 1997). The vast majority of mammalian 5-HT receptors belong to the large GPCR superfamily and couple to adenylate cyclase, either positively (5-HT 4 , 5-HT 6 , and 5-HT 7 ) or negatively (5...