Control of C. elegans larval development by neuronal expression of a TGF-beta homolog

A circuit for navigation in Caenorhabditis elegans

Caenorhabditis elegans explores its environment by interrupting its forward movement with occasional turns and reversals. Turns and reversals occur at stable frequencies but irregular intervals, producing probabilistic exploratory behaviors. Here we dissect the roles of individual sensory neurons, interneurons, and motor neurons in exploratory behaviors under different conditions. After animals are removed from bacterial food, they initiate a local search behavior consisting of reversals and deep omega-shaped turns triggered by AWC olfactory neurons, ASK gustatory neurons, and AIB interneurons. Over the following 30 min, the animals disperse as reversals and omega turns are suppressed by ASI gustatory neurons and AIY interneurons. Interneurons and motor neurons downstream of AIB and AIY encode specific aspects of reversal and turn frequency, amplitude, and directionality. SMD motor neurons help encode the steep amplitude of omega turns, RIV motor neurons specify the ventral bias of turns that follow a reversal, and SMB motor neurons set the amplitude of sinusoidal movement. Many of these sensory neurons, interneurons, and motor neurons are also implicated in chemotaxis and thermotaxis. Thus, this circuit may represent a common substrate for multiple navigation behaviors.

Developmental expression and function of Bmp4 in spermatogenesis and in maintaining epididymal integrity

Bone morphogenetic proteins (BMPs) play essential roles in many aspects of developmental biology. We have previously shown that Bmp7, Bmp8a, and Bmp8b of the 60A class of Bmp genes have additive effects in spermatogenesis and in maintaining the epididymal integrity of the caput and caudal regions. Here we report that Bmp4 of the Dpp class has a unique expression pattern in the developing testis and epididymis. Bmp4 heterozygous males on a largely C57BL/6 background show compromised fertility due to degeneration of germ cells, reduced sperm counts, and decreased sperm motility. More interestingly, some of these males show extensive degeneration of the epididymal epithelium in the corpus region, rather than in the caput and cauda regions as for Bmp7 and Bmp8 mutants. Thus, these genetic data reveal a region-specific requirement of different classes of BMPs for epididymal epithelium to survive and have significant implications on male reproductive health and perhaps birth control.

RNT-1, the C. elegans homologue of mammalian RUNX transcription factors, regulates body size and male tail development

The rnt-1 gene is the only Caenorhabditis elegans homologue of the mammalian RUNX genes. Several lines of molecular biological evidence have demonstrated that the RUNX proteins interact and cooperate with Smads, which are transforming growth factor-beta (TGF-beta) signal mediators. However, the involvement of RUNX in TGF-beta signaling has not yet been supported by any genetic evidence. The Sma/Mab TGF-beta signaling pathway in C. elegans is known to regulate body length and male tail development. The rnt-1(ok351) mutants show the characteristic phenotypes observed in mutants of the Sma/Mab pathway, namely, they have a small body size and ray defects. Moreover, RNT-1 can physically interact with SMA-4 which is one of the Smads in C. elegans, and double mutant animals containing both the rnt-1(ok351) mutation and a mutation in a known Sma/Mab pathway gene displayed synergism in the aberrant phenotypes. In addition, lon-1(e185) mutants was epistatic to rnt-1(ok351) mutants in terms of long phenotype, suggesting that lon-1 is indeed downstream target of rnt-1. Our data reveal that RNT-1 functionally cooperates with the SMA-4 proteins to regulate body size and male tail development in C. elegans.

Regulation of signaling genes by TGFbeta during entry into dauer diapause in C. elegans

Background

When resources are scant, C. elegans larvae arrest as long-lived dauers under the control of insulin/IGF- and TGFβ-related signaling pathways. However, critical questions remain regarding the regulation of this developmental event. How do three dozen insulin-like proteins regulate one tyrosine kinase receptor to control complex events in dauer, metabolism and aging? How are signals from the TGFβ and insulin/IGF pathways integrated? What gene expression programs do these pathways regulate, and how do they control complex downstream events?

Results

We have identified genes that show different levels of expression in a comparison of wild-type L2 or L3 larvae (non-dauer) to TGFβ mutants at similar developmental stages undergoing dauer formation. Many insulin/IGF pathway and other known dauer regulatory genes have changes in expression that suggest strong positive feedback by the TGFβ pathway. In addition, many insulin-like ligand and novel genes with similarity to the extracellular domain of insulin/IGF receptors have altered expression. We have identified a large group of regulated genes with putative binding sites for the FOXO transcription factor, DAF-16. Genes with DAF-16 sites upstream of the transcription start site tend to be upregulated, whereas genes with DAF-16 sites downstream of the coding region tend to be downregulated. Finally, we also see strong regulation of many novel hedgehog- and patched-related genes, hormone biosynthetic genes, cell cycle genes, and other regulatory genes.

Conclusions

The feedback regulation of insulin/IGF pathway and other dauer genes that we observe would be predicted to amplify signals from the TGFβ pathway; this amplification may serve to ensure a decisive choice between "dauer" and "non-dauer", even if environmental cues are ambiguous. Up and down regulation of insulin-like ligands and novel genes with similarity to the extracellular domain of insulin/IGF receptors suggests opposing roles for several members of these large gene families. Unlike in adults, most genes with putative DAF-16 binding sites are upregulated during dauer entry, suggesting that DAF-16 has different activity in dauer versus adult metabolism and aging. However, our observation that the position of putative DAF-16 binding sites is correlated with the direction of regulation suggests a novel method of achieving gene-specific regulation from a single pathway. We see evidence of TGFβ-mediated regulation of several other classes of regulatory genes, and we discuss possible functions of these genes in dauer formation.

A novel nuclear receptor/coregulator complex controls C. elegans lipid metabolism, larval development, and aging

Environmental cues transduced by an endocrine network converge on Caenorhabditis elegans nuclear receptor DAF-12 to mediate arrest at dauer diapause or continuous larval development. In adults, DAF-12 selects long-lived or short-lived modes. How these organismal choices are molecularly specified is unknown. Here we show that coregulator DIN-1 and DAF-12 physically and genetically interact to instruct organismal fates. Homologous to human corepressor SHARP, DIN-1 comes in long (L) and short (S) isoforms, which are nuclear localized but have distinct functions. DIN-1L has embryonic and larval developmental roles. DIN-1S, along with DAF-12, regulates lipid metabolism, larval stage-specific programs, diapause, and longevity. Epistasis experiments reveal that din-1S acts in the dauer pathways downstream of lipophilic hormone, insulin/IGF, and TGFbeta signaling, the same point as daf-12. We propose that the DIN-1S/DAF-12 complex serves as a molecular switch that implements slow life history alternatives in response to diminished hormonal signals.

Alternative polyadenylation results in a truncated daf-4 BMP receptor that antagonizes DAF-7-mediated development in Caenorhabditis elegans

The DAF-4 receptor kinase, which promotes larval development, is encoded by a 2.9 kb mRNA transcribed from the only type II TGF-beta/BMP receptor gene in Caenorhabditis elegans. Here we report that alternative polyadenylation in intron 5 of daf-4 results in a 2.0 kb mRNA that encodes an open reading frame including only the N-terminal secretion signal and ligand-binding domains, and not the transmembrane or kinase domains, of DAF-4. Northern blots and real-time RT-PCR amplifications using RNA samples from developmentally staged animals show that expression levels of both the 2.9 kb and 2.0 kb transcripts are relatively constant, and their abundances similar, except for the transition between non-dauer and dauer stages. In dauer larvae, the steady-state level of the 2.0 kb mRNA increases more than 10-fold and exceeds the 2.9 kb transcript, coincident with an absence of signaling from DAF-4. Transgenic expression of a recombinant daf-4 transgene that encodes only the 2.0 kb mRNA enhances the Daf-c phenotype of a daf-4 hypomorph, whereas the same transgene with a nonsense mutation does not. These data suggest that a polypeptide encoded by the 2.0 kb transcript can function as an antagonist of full-length DAF-4 signaling. Alternative processing of type II receptor transcripts to generate an antagonist is a novel mechanism for negative regulation of a TGF-beta signaling pathway.

Inhibition of bovine T lymphocyte responses by extracts of the stomach worm Ostertagia ostertagi

Lowered immune responses during bovine ostertagiosis have been reported in both in vivo and in vitro assay systems. In the present study we have employed three different life cycle stages of the nematode Ostertagia ostertagi to determine if products of this economically important parasite inhibit in vitro proliferation of Con A-stimulated cells from uninfected animals. We have demonstrated an inhibitory effect upon the growth of Con A-stimulated lymphocytes after addition of fourth stage larval (L4) soluble extract (L4SE) to the cultures. In contrast, extracts from the third stage larvae (L3) had little or no inhibitory activity. The suppressive products were also shown to be secreted by the late L4. The suppressive activity is reversible if the L4 products are removed from culture. There is no immediate effect on proliferating cells and the L4SE must be in culture for 24-48 h before suppression is observable. The L4SE caused slight but not statistically significant decreases in the percentage of T cells and increases in B cell percentages in cultures when compared with cultures stimulated with Con A alone. No changes were seen in percentage of cells positive for markers for CD4, CD8, gammadelta T cells, or monocytes/macrophages as a consequence of the addition of L4SE. In contrast, there was a strong and significant reduction in the expression of the IL-2 receptors in cells cultured in the presence of the worm extract. There was no evidence of either necrosis or apoptosis resulting from the presence of L4 products in culture. The expression of messenger RNA for interleukin-2, -4, -13, tumor necrosis factor-alpha (TNF-alpha), and gamma-interferon (gamma-IFN) was decreased when L4SE was included in cultures of Con A-stimulated cells compared to cultures stimulated with Con A only. In contrast, messenger RNA expression of transforming growth factor-beta (TGF-beta) and interleukin-10 (IL-10) was increased in cells growing in the presence of L4 products. The potential role of these cytokines during ostertagiosis is discussed.

Insulinoma-Associated Protein IA-2, a Vesicle Transmembrane Protein, Genetically Interacts with UNC-31/CAPS and Affects Neurosecretion in Caenorhabditis elegans

IA-2 (insulinoma-associated protein 2), a major autoantigen in type 1 diabetes, is a receptor-tyrosine phosphatase-like protein associated with the membrane of secretory granules of neural and endocrine-specific cells. Loss of IA-2 activity in the mouse results in reduced insulin release and additional phenotypes, consistent with a general effect on neurosecretion and hormone release. To gain further insight into the cellular mechanisms of IA-2 function, we have studied the Caenorhabditis elegans homolog, CeIA-2 encoded by the ida-1 gene. Using two independent putative null alleles of ida-1, we demonstrate that animals lacking CeIA-2 activity are viable and exhibit subtle defects. Genetic studies of mutants in ida-1 and several genes involved in neurosecretory vesicle cargo release and signaling highlight two roles for CeIA-2. First, CeIA-2 has a specific and novel genetic interaction with UNC-31/CAPS, a protein that has been shown in other systems to regulate dense-core vesicle cargo release. Second, loss of CeIA-2 activity enhances weak alleles in the insulin-like signaling pathway. These results suggest that CeIA-2 may be an important factor in dense-core vesicle cargo release with parallels to insulin signaling in mammals.

Systematic interactome mapping and genetic perturbation analysis of a C. elegans TGF-beta signaling network

To initiate a system-level analysis of C. elegans DAF-7/TGF-beta signaling, we combined interactome mapping with single and double genetic perturbations. Yeast two-hybrid (Y2H) screens starting with known DAF-7/TGF-beta pathway components defined a network of 71 interactions among 59 proteins. Coaffinity purification (co-AP) assays in mammalian cells confirmed the overall quality of this network. Systematic perturbations of the network using RNAi, both in wild-type and daf-7/TGF-beta pathway mutant animals, identified nine DAF-7/TGF-beta signaling modifiers, seven of which are conserved in humans. We show that one of these has functional homology to human SNO/SKI oncoproteins and that mutations at the corresponding genetic locus daf-5 confer defects in DAF-7/TGF-beta signaling. Our results reveal substantial molecular complexity in DAF-7/TGF-beta signal transduction. Integrating interactome maps with systematic genetic perturbations may be useful for developing a systems biology approach to this and other signaling modules.

Expression and function of conserved nuclear receptor genes in Caenorhabditis elegans

The Caenorhabditis elegans genome encodes 284 nuclear receptor (NR) genes. Among these 284 NR genes are 15 genes conserved among the Metazoa. Here, we analyze the expression and function of eight heretofore uncharacterized conserved C. elegans NR genes. Reporter gene analysis demonstrates that these genes have distinct expression patterns and that a majority of the C. elegans cell types express a conserved NR gene. RNA interference with NR gene function resulted in visible phenotypes for three of the genes, revealing functions in various processes during postembryonic development. Five of the conserved NR genes are orthologs of NR genes that function during molting and metamorphosis in insects. Functional studies confirm a role for most of these 'ecdysone cascade' NR orthologs during the continuous growth and dauer molts. Transcript levels for these genes fluctuate in a reiterated pattern during the molting cycles, reminiscent of the expression hierarchy observed in the insect ecdysone response. Together, these analyses provide a foundation for further dissecting the role of NRs in nematode development as well as for evaluating conservation of NR functions among the Metazoa.

Molecular biology of reproduction and development in parasitic nematodes: progress and opportunities

Molecular biological research on the development and reproduction of parasites is of major significance for many fundamental and applied areas of medical and veterinary parasitology. Together with knowledge of parasite biology and epidemiology, the application of molecular tools and technologies provides unique opportunities for elucidating developmental and reproductive processes in helminths. This article focuses specifically on recent progress in studying the molecular mechanisms of development, sexual differentiation and reproduction in parasitic nematodes of socio-economic importance and comparative analyses, where appropriate, with the free-living nematode Caenorhabditis elegans. It also describes the implications of such work for understanding reproduction, tissue migration, hypobiosis, signal transduction and host-parasite interactions at the molecular level, and for seeking new means of parasite intervention.

The voltage-gated calcium channel UNC-2 is involved in stress-mediated regulation of tryptophan hydroxylase

Migraine is an episodic pain disorder whose pathophysiology is related to deficiency of serotonin signaling and abnormal function of the P/Q-type calcium channel, CACNA1A. Because the relationship of the CACNA1A channel to serotonin signaling is unknown and potentially of therapeutic interest we have used genetic analysis of the Caenorhabditis elegans ortholog of this calcium channel, UNC-2, to help identify candidate downstream effectors of the human channel. By genetic dissection of the lethargic mutant phenotype of unc-2, we have established an epistasis pathway showing that UNC-2 function antagonizes a transforming growth factor (TGF)-beta pathway influencing movement rate. This same UNC-2/TGF-beta pathway is required for accumulation of normal serotonin levels and stress-induced modulation of tryptophan hydroxylase (tph) expression in the serotonergic chemosensory ADF neurons, but not the NSM neurons. We also show that transgenic expression of the migraine-associated Ca2+ channel, CACNA1A, in unc-2 animals can functionally substitute for UNC-2 in stress-activated regulation of tph expression. The demonstration that these evolutionarily related channels share a conserved ability to modulate tph expression through their effects on TGF-beta signaling provides the first specific example of how CACNA1A function may influence levels of the critical migraine neurotransmitter serotonin.

Ascorbic acid is a requirement for the morphogenesis of the human filarial parasite Brugia malayi

The nematode parasites Wuchereria bancrofti, Brugia malayi, and B. timori cause a disease in humans known as lymphatic filariasis, which afflicts approximately 120 million people worldwide. The parasites enter the human host from the mosquito either as L3 or as infective larvae and subsequently differentiate through 2 molts. In this article, we show that B. malayi depends on an exogenous source of vitamin C to complete the L3 to L4 molt, a critical morphogenic step in its life cycle. Brugia malayi apparently belongs to a small group of living organisms that depend on an exogenous source of vitamin C. This group includes only primates (including man) and guinea pigs among mammals.

Isolation and Characterization of High-Temperature-Induced Dauer Formation Mutants in Caenorhabditis elegans

Dauer formation in Caenorhabditis elegans is regulated by at least three signaling pathways, including an insulin receptor-signaling pathway. These pathways were defined by mutants that form dauers constitutively (Daf-c) at 25°. Screens for Daf-c mutants at 25° have probably been saturated, but failed to identify all the components involved in regulating dauer formation. Here we screen for Daf-c mutants at 27°, a more strongly dauer-inducing condition. Mutations identified include novel classes of alleles for three known genes and alleles defining at least seven new genes, hid-1–hid-7. Many of the genes appear to act in the insulin branch of the dauer pathway, including pdk-1, akt-1, aex-6, and hid-1. We also molecularly identify hid-1 and show that it encodes a novel highly conserved putative transmembrane protein expressed in neurons.

SKN-1 links C. elegans mesendodermal specification to a conserved oxidative stress response

During the earliest stages of Caenorhabditis elegans embryogenesis, the transcription factor SKN-1 initiates development of the digestive system and other mesendodermal tissues. Postembryonic SKN-1 functions have not been elucidated. SKN-1 binds to DNA through a unique mechanism, but is distantly related to basic leucine-zipper proteins that orchestrate the major oxidative stress response in vertebrates and yeast. Here we show that despite its distinct mode of target gene recognition, SKN-1 functions similarly to resist oxidative stress in C. elegans. During postembryonic stages, SKN-1 regulates a key Phase II detoxification gene through constitutive and stress-inducible mechanisms in the ASI chemosensory neurons and intestine, respectively. SKN-1 is present in ASI nuclei under normal conditions, and accumulates in intestinal nuclei in response to oxidative stress. skn-1 mutants are sensitive to oxidative stress and have shortened lifespans. SKN-1 represents a connection between developmental specification of the digestive system and one of its most basic functions, resistance to oxidative and xenobiotic stress. This oxidative stress response thus appears to be both widely conserved and ancient, suggesting that the mesendodermal specification role of SKN-1 was predated by its function in these detoxification mechanisms.

TGF-betas and their roles in the regulation of neuron survival

Transforming growth factor-betas (TGF-betas) are a still growing superfamily of cytokines with widespread distribution and diverse biological functions. They fall into several subfamilies including the TGF-betas 1, 2, and 3, the bone morphogenetic proteins (BMPs), the growth/differentiation factors (GDFs), activins and inhibins, and the members of the glial cell line-derived neurotrophic factor family. Following a brief description of their general roles and signaling in development, maintenance of homeostasis, and disease, we shall focus on their distribution in the CNS and their involvement in regulating neuron survival and death.

SAGE surveys C. elegans carbohydrate metabolism: evidence for an anaerobic shift in the long-lived dauer larva

The dauer larva, a non-feeding and developmentally arrested stage of the free-living nematode Caenorhabditis elegans, is morphologically and physiologically specialized for survival and dispersal during adverse growth conditions. The ability of dauer larvae to live several times longer than the continuous developmental life span has been attributed in part to a repressed metabolism. We used serial analysis of gene expression (SAGE) profiles from dauer larvae and mixed growing stages to compare expression patterns for genes with known or predicted roles in glycolysis, gluconeogenesis, glycogen metabolism, the Krebs and glyoxylate cycles, and selected fermentation pathways. Ratios of mixed:dauer transcripts indicated non-dauer enrichment that was consistent with previously determined adult:dauer enzyme activity ratios for hexokinase (glycolysis), phosphoenolpyruvate carboxykinase and fructose 1,6-bisphosphatase (gluconeogenesis), isocitrate dehydrogenase (NADP-dependent), and isocitrate lyase-malate synthase (glyoxylate cycle). Transcripts for the majority of Krebs cycle components were not differentially represented in the two profiles. Transcript abundance for pyruvate kinase, alcohol dehydrogenase, a putative cytosolic fumarate reductase, two pyruvate dehydrogenase components, and a succinyl CoA synthetase alpha subunit implied that anaerobic pathways were upregulated in dauer larvae. Generation of nutritive fermentation byproducts and the moderation of oxidative damage are potential benefits of a hypoxic dauer interior.

Bone marrow immunohistochemical studies of angiogenic cytokines and their receptors in myelofibrosis with myeloid metaplasia

Bone marrow specimens from 11 patients with myelofibrosis with myeloid metaplasia (MMM) and seven normal controls were studied immunohistochemically to determine expression of transforming growth factor beta (TGF-beta), platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) and corresponding receptors. Staining distribution and intensity for TGF-beta, PDGF, VEGF, TGF-beta type II receptor, a receptor for PDGF, and receptors for VEGF and bFGF were similar in patients and controls. Bone marrow from 10 MMM patients showed increased TGF-beta type I receptor (TGF-betaRI) expression in small vessel endothelial cells. Eight patient specimens had bFGF overexpression in megakaryocytes. Increased microvessel density and decreased concentration of bFGF-staining stromal cells accompanied these changes. Microvascular TGF-betaRI upregulation and bFGF overexpression by megakaryocytes may cause bone marrow microenvironmental changes in MMM patients.

Caenorhabditis elegans: an emerging genetic model for the study of innate immunity

Invaluable insights into how animals, humans included, defend themselves against infection have been provided by more than a decade of genetic studies that have used fruitflies. In the past few years, attention has also turned to another simple animal model, the nematode worm Caenorhabditis elegans. What exactly have we learned from the work in Drosophila? And will research with C. elegans teach us anything new about our response to pathogen attack?

daf-28 encodes a C. elegans insulin superfamily member that is regulated by environmental cues and acts in the DAF-2 signaling pathway

In Caenorhabditis elegans, the decision to enter a developmentally arrested dauer larval stage is triggered by a combination of signals from sensory neurons in response to environmental cues, which include a dauer pheromone. These sensory inputs are coupled to the parallel DAF-2/insulin receptor-like and DAF-7/TGFbeta-like signaling pathways. Although sensory inputs have been shown to physiologically regulate DAF-7/TGFbeta expression, no such regulation of insulin-like ligands in the DAF-2 pathway has been reported. We show here that daf-28 encodes an insulin-like protein, which when mutated causes dauer arrest and down-regulation of DAF-2/IR signaling. A daf-28GFP fusion gene is expressed in ASI and ASJ, two sensory neurons that regulate dauer arrest. daf-28GFP expression in ASI and ASJ is down-regulated under dauer-inducing conditions and in mutants of DAF-11/guanylyl cyclase, a predicted component of the dauer-pheromone-sensing pathway. Thus, daf-28 expression in sensory neurons is regulated by the environmental cues that normally trigger dauer arrest. Among the 38 C. elegans insulin genes, daf-28 is so far the only insulin mutant to affect dauer arrest. daf-28 was revealed from this functional redundancy by a dominant-negative allele that disrupts a probable proteolytic processing site required for insulin maturation. This DAF-28 mutant is likely to be poisonous to wild-type DAF-28 and other insulins.

A divergent INS protein in Caenorhabditis elegans structurally resembles human insulin and activates the human insulin receptor

Caenorhabditis elegans contains a family of putative insulin-like genes proposed to regulate dauer arrest and senescence. These sequences often lack characteristic sequence features of human insulin essential for its folding, structure, and function. Here, we describe the structure and receptor-binding properties of INS-6, a single-chain polypeptide expressed in specific neurons. Despite multiple nonconservative changes in sequence, INS-6 recapitulates an insulin-like fold. Although lacking classical receptor-binding determinants, INS-6 binds to and activates the human insulin receptor. Its activity is greater than that of an analogous single-chain human insulin analog.

Genetic screen for small body size mutants in C. elegans reveals many TGFbeta pathway components

In the nematode Caenorhabditis elegans, a TGFbeta-related signaling pathway regulates body size and male tail morphogenesis. We sought to identify genes encoding components or modifiers of this pathway in a large-scale genetic screen. Remarkably, this screen was able to identify essentially all core components of the TGFbeta signaling pathway. Among 34 Small mutants, many mutations disrupt genes encoding recognizable components of the TGFbeta pathway: DBL-1 ligand, DAF-4 type II receptor, SMA-6 type I receptor, and SMA-2, SMA-3, and SMA-4 Smads. Moreover, we find that at least 11 additional complementation groups can mutate to the Small phenotype. Four of these 11 genes, sma-9, sma-14, sma-16, and sma-20 affect male tail morphogenesis as well as body size. Two genes, sma-11 and sma-20, also influence regulation of the developmentally arrested dauer larval stage, suggesting a role in a second characterized TGFbeta pathway in C. elegans. Other genes may represent tissue-specific factors or parallel pathways for body size control. Because of the conservation of TGFbeta signaling pathways, homologs of these genes may be involved in tissue specificity and/or crosstalk of TGFbeta pathways in other animals.

TGF-beta signaling activates steroid hormone receptor expression during neuronal remodeling in the Drosophila brain

Metamorphosis of the Drosophila brain involves pruning of many larval-specific dendrites and axons followed by outgrowth of adult-specific processes. From a genetic mosaic screen, we recovered two independent mutations that block neuronal remodeling in the mushroom bodies (MBs). These phenotypically indistinguishable mutations affect Baboon function, a Drosophila TGF-beta/activin type I receptor, and dSmad2, its downstream transcriptional effector. We also show that Punt and Wit, two type II receptors, act redundantly in this process. In addition, knocking out dActivin around the mid-third instar stage interferes with remodeling. Binding of the insect steroid hormone ecdysone to distinct ecdysone receptor isoforms induces different metamorphic responses in various larval tissues. Interestingly, expression of the ecdysone receptor B1 isoform (EcR-B1) is reduced in activin pathway mutants, and restoring EcR-B1 expression significantly rescues remodeling defects. We conclude that the Drosophila Activin signaling pathway mediates neuronal remodeling in part by regulating EcR-B1 expression.

Invertebrate Humoral Factors: Cytokines as Mediators of Cell Survival

The presence and the different functional aspects of cytokine-related molecules in invertebrates are described. Cytokine-like factors affect immune functions, such as cell motility, chemotaxis, phagocytosis and cytotoxicity. In particular, cell migration shows a species-specific effect for IL-1alpha and TNF-alpha and a dose-correlated effect for IL-8, PDGF-AB and TGF-beta1. Apart from some exceptions, the phagocytic effect increases significantly at all the concentrations tested and with all the species used. PDGF-AB, TGF-beta1 and IL-8 provoke conformational changes in mollusk immunocytes, involving the signaling transduction pathways of phosphatidylinositol and cAMP. PDGF-AB and TGF-beta1 partially inhibit the induced programmed cell death in an insect cell line, and the survival effect is mediated by the activation of phosphatidylinositol 3-kinase, PKA and PKC. The exogenous administration of these growth factors in an invertebrate wound repair model showed that they are able to control the wound environment and promote the repair process by accelerating the coordinated activities involved. Moreover, IL-1alpha, IL-2 and TNF-alpha are able to induce nitric oxide synthase. PDGF-AB and TGF-beta1 provoke an increase in neutral endopeptidase-24.11 (NEP)-like activity in membrane preparations from mollusk immunocytes, while NEP deactivates the PDGF-AB- and TGF-beta1-induced cell shape changes. Cytokines are also involved in invertebrate stress response in a manner extremely similar to that in vertebrates. Several studies suggest the existence on the mollusk immunocyte membrane of an ancestral receptor capable of binding both IL-2 and CRH. Furthermore, the competition found between CRH and a large number of cytokines supports the idea that invertebrate cytokine receptors show a certain degree of promiscuity. The multiple functions of cytokines detected in invertebrates underline another characteristic of mammalian cytokines, i.e. their great pleiotropicity. Altogether, the studies on the function of the invertebrate humoral factors show a close overlapping with those found in vertebrates, and the hypothesized missing correlation between invertebrate and vertebrate cytokine genes that is emerging from the limited molecular biology data present in literature might represent a very peculiar strategy followed by Nature in the evolution of cytokines.

Functional convergence of invertebrate and vertebrate cytokine-like molecules based on a similar lectin-like activity

It is generally accepted that the action of cytokines results from their binding to specific receptors. However, many cytokines possess lectin-like activity that may be essential for the expression of their full biological activities. This review focuses on the physiological relevance of the lectin-like activity of cytokines during the innate immune response in mammals, using TNF as an illustrative example. Moreover, we will show that TNF displays functional analogies with a defense molecule from the earthworm Eisenia foetida termed CCF. These analogies are not reflected by primary sequence homology between CCF and TNF but are particularly based on a similar lectin-like activity/domain. Hence, from a phylogenetic point of view, the lectin-like activity/domain of CCF and TNF may represent an essential recognition mechanism that has been functionally conserved during the innate immune response of invertebrates and vertebrates as a result of convergent evolution.

Molecular approaches to aggregation behavior and social attachment

In many animal species individuals aggregate to live in groups. A range of experimental approaches in different animals, including studies of social feeding in nematodes, maternal behavior in rats and sheep, and pair-bonding in voles, are providing insights into the neural bases for these behaviors. These studies are delineating multiple neural circuits and gene networks in the brain that interact in ways that are as yet poorly understood to coordinate social behavior.

Positive selection of Caenorhabditis elegans mutants with increased stress resistance and longevity

We developed selective conditions for long-lived mutants of the nematode Caenorhabditis elegans by subjecting the first larval stage (L1) to thermal stress at 30 degrees for 7 days. The surviving larvae developed to fertile adults after the temperature was shifted to 15 degrees. A total of one million F(2) progeny and a half million F(3) progeny of ethyl-methanesulfonate-mutagenized animals were treated in three separate experiments. Among the 81 putative mutants that recovered and matured to the reproductive adult, 63 retested as thermotolerant and 49 (80%) exhibited a >15% increase in mean life span. All the known classes of dauer formation (Daf) mutant that affect longevity were found, including six new alleles of daf-2, and a unique temperature-sensitive, dauer-constitutive allele of age-1. Alleles of dyf-2 and unc-13 were isolated, and mutants of unc-18, a gene that interacts with unc-13, were also found to be long lived. Thirteen additional mutations define at least four new genes.

The DAF-7 TGF-beta signaling pathway regulates chemosensory receptor gene expression in C. elegans

Regulation of chemoreceptor gene expression in response to environmental or developmental cues provides a mechanism by which animals can alter their sensory responses. Here we demonstrate a role for the daf-7 TGF-beta pathway in the regulation of expression of a subset of chemoreceptor genes in Caenorhabditis elegans. We describe a novel role of this pathway in maintaining receptor gene expression in the adult and show that the DAF-4 type II TGF-beta receptor functions cell-autonomously to modulate chemoreceptor expression. We also find that the alteration of receptor gene expression in the ASI chemosensory neurons by environmental signals, such as levels of a constitutively produced pheromone, may be mediated via a DAF-7-independent pathway. Receptor gene expression in the ASI and ASH sensory neurons appears to be regulated via distinct mechanisms. Our results suggest that the expression of individual chemoreceptor genes in C. elegans is subject to multiple modes of regulation, thereby ensuring that animals exhibit the responses most appropriate for their developmental stage and environmental conditions.

Extracellular regulation of BMP signaling in vertebrates: a cocktail of modulators

The transforming growth factor-beta (TGF-beta) superfamily contains a variety of growth factors which all share common sequence elements and structural motifs. These proteins are known to exert a wide spectrum of biological responses on a large variety of cell types in both vertebrates and invertebrates. Many of them have important functions during embryonic development in pattern formation and tissue specification, and in adult tissues, they are involved in processes such as wound healing, bone repair, and bone remodeling. The family is divided into two general branches: the BMP/GDF and the TGF-beta/Activin/Nodal branches, whose members have diverse, often complementary effects. It is obvious that an orchestered regulation of different actions of these proteins is necessary for proper functioning. The TGF-beta family members act by binding extracellularly to a complex of serine/threonine kinase receptors, which consequently activate Smad molecules by phosphorylation. These Smads translocate to the nucleus, where they modulate transcription of specific genes. Three levels by which this signaling pathway is regulated could be distinguished. First, a control mechanism exists in the intracellular space, where inhibitory Smads and Smurfs prevent further signaling and activation of target genes. Second, at the membrane site, the pseudoreceptor BAMBI/Nma is able to inhibit further signaling within the cells. Finally, a range of extracellular mediators are identified which modulate the functioning of members of the TGF-beta superfamily. Here, we review the insights in the extracellular regulation of members of the BMP subfamily of secreted growth factors with a major emphasis on vertebrate BMP modulation.

Social feeding in Caenorhabditis elegans is induced by neurons that detect aversive stimuli

Natural Caenorhabditis elegans isolates exhibit either social or solitary feeding on bacteria. We show here that social feeding is induced by nociceptive neurons that detect adverse or stressful conditions. Ablation of the nociceptive neurons ASH and ADL transforms social animals into solitary feeders. Social feeding is probably due to the sensation of noxious chemicals by ASH and ADL neurons; it requires the genes ocr-2 and osm-9, which encode TRP-related transduction channels, and odr-4 and odr-8, which are required to localize sensory chemoreceptors to cilia. Other sensory neurons may suppress social feeding, as social feeding in ocr-2 and odr-4 mutants is restored by mutations in osm-3, a gene required for the development of 26 ciliated sensory neurons. Our data suggest a model for regulation of social feeding by opposing sensory inputs: aversive inputs to nociceptive neurons promote social feeding, whereas antagonistic inputs from neurons that express osm-3 inhibit aggregation.

Increased or decreased levels of Caenorhabditis elegans lon-3, a gene encoding a collagen, cause reciprocal changes in body length

Body length in C. elegans is regulated by a member of the TGFbeta family, DBL-1. Loss-of-function mutations in dbl-1, or in genes encoding components of the signaling pathway it activates, cause worms to be shorter than wild type and slightly thinner (Sma). Overexpression of dbl-1 confers the Lon phenotype characterized by an increase in body length. We show here that loss-of-function mutations in dbl-1 and lon-1, respectively, cause a decrease or increase in the ploidy of nuclei in the hypodermal syncytial cell, hyp7. To learn more about the regulation of body length in C. elegans we carried out a genetic screen for new mutations causing a Lon phenotype. We report here the cloning and characterization of lon-3. lon-3 is shown to encode a putative cuticle collagen that is expressed in hypodermal cells. We show that, whereas putative null mutations in lon-3 (or reduction of lon-3 activity by RNAi) causes a Lon phenotype, increasing lon-3 gene copy number causes a marked reduction in body length. Morphometric analyses indicate that the lon-3 loss-of-function phenotype resembles that caused by overexpression of dbl-1. Furthermore, phenotypes caused by defects in dbl-1 or lon-3 expression are in both cases suppressed by a null mutation in sqt-1, a second cuticle collagen gene. However, whereas loss of dbl-1 activity causes a reduction in hypodermal endoreduplication, the reduction in body length associated with overexpression of lon-3 occurs in the absence of defects in hypodermal ploidy.

Transforming growth factor-beta and insulin-like signalling pathways in parasitic helminths

The signal transduction pathways involved in regulating developmental arrest in the free-living nematode, Caenorhabditis elegans, are fairly well characterised. However, much less is known about how these processes may influence the developmental timing and maturation in helminth parasites. Here, we provide an overview of two signalling pathways implicated in the regulation of dauer larva formation in C. elegans, the insulin-like signalling pathway and the transforming growth factor-beta pathway, and explore what is known about these signalling pathways in a variety of parasitic helminths. Understanding the differences about how these pathways are affected by environmental cues in free-living versus parasitic species of helminths may provide insights into novel mechanisms for the control or prevention of helminth-induced disease.

Neurotoxin-induced degeneration of dopamine neurons in Caenorhabditis elegans

Parkinson's disease is a complex neurodegenerative disorder characterized by the death of brain dopamine neurons. In mammals, dopamine neuronal degeneration can be triggered through exposure to neurotoxins accumulated by the presynaptic dopamine transporter (DAT), including 6-hydroxydopamine (6-OHDA) and 1-methyl-4-phenylpyridinium. We have established a system for the pharmacological and genetic evaluation of neurotoxin-induced dopamine neuronal death in Caenorhabditis elegans. Brief (1 h) exposure of green fluorescent protein-tagged, living worms to 6-OHDA causes selective degeneration of dopamine neurons. We demonstrate that agents that interfere with DAT function protect against 6-OHDA toxicity. 6-OHDA-triggered neural degeneration does not require the CED-3/CED-4 cell death pathway, but is abolished by the genetic disruption of the C. elegans DAT.

A Caenorhabditis elegans TGF-beta, DBL-1, controls the expression of LON-1, a PR-related protein, that regulates polyploidization and body length

Using cDNA-based array analysis combined with double-stranded RNA interference (dsRNAi), we have identified yk298h6 as a target gene of Caenorhabditis elegans TGF-beta signaling. Worms overexpressing dbl-1, a TGF-beta ligand, are 16% longer than wild type. Array analysis shows yk298h6 to be one of several genes suppressed in such worms. Disruption of yk298h6 function by dsRNAi also resulted in long worms, suggesting that it is a negative regulator of body length. yk298h6 was then mapped to, and shown to be identical to, lon-1, a known gene that affects body length. lon-1 encodes a 312 amino acid protein with a motif sequence that is conserved from plants to humans. Expression studies confirm that LON-1 is repressed by DBL-1, suggesting that LON-1 is a novel downstream component of the C.elegans TGF-beta growth regulation pathway. Consistent with this, LON-1 is expressed mainly in the larval and adult hypodermis and has dose-dependent effects on body length associated with changes in hypodermal ploidy, but not hypodermal cell proliferation.

Regulation of chemosensory receptor expression and sensory signaling by the KIN-29 Ser/Thr kinase

Sensory signals regulate multiple developmental and behavioral circuits in C. elegans, providing a genetically tractable system in which to investigate the mechanisms underlying the acquisition and integration of sensory information. kin-29 mutants are defective in the expression of a set of chemoreceptor genes, and exhibit characteristics associated with altered sensory signaling, including increased lifespan, decreased body size, and deregulated entry into the dauer developmental stage. kin-29 encodes a Ser/Thr kinase with similarity to the MARK and AMPK/SNF1 family of kinases. We show that KIN-29 acts cell-autonomously and non-cell-autonomously in sensory neurons to regulate chemoreceptor expression, body size, and the dauer decision, suggesting that kin-29 function is essential for the correct acquisition and transduction of sensory information.

The genetics of aging

The genetic analysis of life span has only begun in mammals, invertebrates, such as Caenorhabditis elegans and Drosophila, and yeast. Even at this primitive stage of the genetic analysis of aging, the physiological observations that rate of metabolism is intimately tied to life span is supported. In many examples from mice to worms to flies to yeast, genetic variants that affect life span also modify metabolism. Insulin signaling regulates life span coordinately with reproduction, metabolism, and free radical protective gene regulation in C. elegans. This may be related to the findings that caloric restriction also regulates mammalian aging, perhaps via the modulation of insulin-like signaling pathways. The nervous system has been implicated as a key tissue where insulin-like signaling and free radical protective pathways regulate life span in C. elegans and Drosophila. Genes that determine the life span could act in neuroendocrine cells in diverse animals. The involvement of insulin-like hormones suggests that the plasticity in life spans evident in animal phylogeny may be due to variation in the timing of release of hormones that control vitality and mortality as well as variation in the response to those hormones. Pedigree analysis of human aging may reveal variations in the orthologs of the insulin pathway genes and coupled pathways that regulate invertebrate aging. Thus, genetic approaches may identify a set of circuits that was established in ancestral metazoans to regulate their longevity.

Targets of TGF beta-related signaling in Caenorhabditis elegans

With the characterization of the Smads 5 years ago, it became possible to trace the TGFbeta signal transduction pathway from the plasma membrane to the nucleus. Since that time, many Smad interaction partners, cofactors and target genes have been identified using a variety of experimental approaches and model systems. Understanding how these partners generate tissue specificity and crosstalk between pathways is an ongoing pursuit for the field of TGFbeta signal transduction. The nematode Caenorhabditis elegans provides a simple, genetically tractable model organism in which to address this goal. This review will examine progress towards the identification of cellular and molecular targets of TGFbeta-related signaling in C. elegans.

Hypodermal expression of Caenorhabditis elegans TGF-beta type I receptor SMA-6 is essential for the growth and maintenance of body length

There are several transforming growth factor-beta (TGF-beta) pathways in the nematode Caenorhabditis elegans. One of these pathways regulates body length and is composed of the ligand DBL-1, serine/threonine protein kinase receptors SMA-6 and DAF-4, and cytoplasmic signaling components SMA-2, SMA-3, and SMA-4. To further examine the molecular mechanisms of body-length regulation in the nematode by the TGF-beta pathway, we examined the regional requirement for the type-I receptor SMA-6. Using a SMA-6::GFP (green fluorescent protein) reporter gene, sma-6 was highly expressed in the hypodermis, unlike the type-II receptor DAF-4, which is reported to be ubiquitously expressed. We then examined the ability of SMA-6 expression in different regions of the C. elegans body to rescue the sma-6 phenotype (small) and found that hypodermal expression of SMA-6 is necessary and sufficient for the growth and maintenance of body length. We also demonstrate that GATA sequences in the sma-6 promoter contribute to the hypodermal expression of sma-6.

A hormonal signaling pathway influencing C. elegans metabolism, reproductive development, and life span

During C. elegans development, animals must choose between reproductive growth or dauer diapause in response to sensory cues. Insulin/IGF-I and TGF-beta signaling converge on the orphan nuclear receptor daf-12 to mediate this choice. Here we show that daf-9 acts downstream of these inputs but upstream of daf-12. daf-9 and daf-12 mutants have similar larval defects and modulate insulin/IGF-I and gonadal signals that regulate adult life span. daf-9 encodes a cytochrome P450 related to vertebrate steroidogenic hydroxylases, suggesting that it could metabolize a DAF-12 ligand. Sterols may be the daf-9 substrate and daf-12 ligand because cholesterol deprivation phenocopies mutant defects. Sensory neurons, hypodermis, and somatic gonadal cells expressing daf-9 identify potential endocrine tissues. Evidently, lipophilic hormones influence nematode metabolism, diapause, and life span.

DAF-7/TGF-beta expression required for the normal larval development in C. elegans is controlled by a presumed guanylyl cyclase DAF-11

In C. elegans development, unfavorable growth conditions lead a larva to an arrested and enduring form called a dauer. To elucidate components upstream of DAF-7/TGF-beta in this control pathway, we isolated a mutant that was defective in daf-7 promoter::gfp reporter expression and showed an arrested (dauer-constitutive) phenotype. It has a new mutation in the daf-11 gene encoding a transmembrane guanylyl cyclase. We show that daf-11 gene and a related gene daf-21 act upstream of daf-7, and cilium-related genes che-2 and che-3 are placed between daf-11 and daf-7, in the genetic pathway controlling dauer formation. Expression of daf-11 cDNA by cell specific promoters suggests that daf-11 acts cell autonomously in ASI chemosensory neurons for daf-7 expression.

Sensory experience and sensory activity regulate chemosensory receptor gene expression in Caenorhabditis elegans

Changes in the environment cause both short-term and long-term changes in an animal's behavior. Here we show that specific sensory experiences cause changes in chemosensory receptor gene expression that may alter sensory perception in the nematode Caenorhabditis elegans. Three predicted chemosensory receptor genes expressed in the ASI chemosensory neurons, srd-1, str-2, and str-3, are repressed by exposure to the dauer pheromone, a signal of crowding. Repression occurs at pheromone concentrations below those that induce formation of the alternative dauer larva stage, suggesting that exposure to pheromones can alter the chemosensory behaviors of non-dauer animals. In addition, ASI expression of srd-1, but not str-2 and str-3, is induced by sensory activity of the ASI neurons. Expression of two receptor genes is regulated by developmental entry into the dauer larva stage. srd-1 expression in ASI neurons is repressed in dauer larvae. str-2 expression in dauer animals is induced in the ASI neurons, but repressed in the AWC neurons. The ASI and AWC neurons remodel in the dauer stage, and these results suggest that their sensory specificity changes as well. We suggest that experience-dependent changes in chemosensory receptor gene expression may modify olfactory behaviors.

In vitro reactivation of Ancylostoma caninum tissue-arrested third-stage larvae by transforming growth factor-beta

Developmental arrest in Ancylostoma caninum is associated with preparasitic, free-living third-stage (L3) larvae, as well as anthelmintic-resilient hypobiotic L3 larvae within the tissues of an infected dog. With the tissue-arrested larvae, pregnancy and, more specifically, the hormonal effects of estrogen and prolactin mediate reactivation resulting in transmammary transmission of infection to nursing puppies. Estrogen and prolactin have been shown to be critically involved in upregulation of transforming growth factor (TGF)-beta2 during pregnancy, and studies on the soil nematode Caenorhabditis elegans further implicate TGF-beta and insulin-like signaling pathways with larval arrest and reactivation. In this report, an in vitro assay was used to show that neither estrogen, prolactin, nor insulin had a direct effect on the feeding/reactivation response of tissue-arrested larvae; however, TGF-beta isoforms 1 and 2 both had significant stimulatory effects that were comparable to the effects of dog serum. The stimulatory effects of serum could be blocked by preincubation with anti-TGF-beta antibodies. Taken together, the results support the hypothesis that during pregnancy, host-derived TGF-beta can signal a parasite-encoded receptor to trigger the reactivation of tissue-arrested larvae. TGF-beta had no effect on preparasitic larvae, suggesting that different signals may be involved in reactivation of the 2 different arrested forms of A. caninum L3 larvae.

Platelet-derived growth factor and transforming growth factor-beta in invertebrate immune and neuroendocrine interactions: another sign of conservation in evolution

Growth factor-like molecules have been found in various invertebrate species. In particular, we have reported the presence of platelet-derived growth factor (PDGF)-AB and transforming growth factor-beta (TGF-beta)1 immunoreactive molecules in molluscs, insects and annelids. Moreover, PDGF-AB and TGF-beta1 affect the main immune functions, such as phagocytosis, chemotaxis and cell motility. Changes in cell shape are induced via interactions of growth factors with their respective specific receptors. The extracellular signals are transduced by the activation of classical signal transduction pathways, such as those involving PKA and PKC, and pivotal transcription regulators, i.e. the Fos, Jun and SMAD proteins. The two growth factors intervene in stress responses by activating the CRH-ACTH-biogenic amine axis. Exogenous administration of PDGF-AB and TGF-beta1 in a molluscan wound provokes an accelerated migration of immunocytes and fibroblasts to the injured area, stimulating granulation tissue formation and wound re-epithelialization. These findings suggest that these molecules are ancestral and that their function is well conserved and crucial in the maintenance of invertebrate homeostasis.

Changes in gene expression associated with developmental arrest and longevity in Caenorhabditis elegans

Gene expression in a developmentally arrested, long-lived dauer population of Caenorhabditis elegans was compared with a nondauer (mixed-stage) population by using serial analysis of gene expression (SAGE). Dauer (152,314) and nondauer (148,324) SAGE tags identified 11,130 of the predicted 19,100 C. elegans genes. Genes implicated previously in longevity were expressed abundantly in the dauer library, and new genes potentially important in dauer biology were discovered. Two thousand six hundred eighteen genes were detected only in the nondauer population, whereas 2016 genes were detected only in the dauer, showing that dauer larvae show a surprisingly complex gene expression profile. Evidence for differentially expressed gene transcript isoforms was obtained for 162 genes. H1 histones were differentially expressed, raising the possibility of alternative chromatin packaging. The most abundant tag from dauer larvae (20-fold more abundant than in the nondauer profile) corresponds to a new, unpredicted gene we have named tts-1 (transcribed telomere-like sequence), which may interact with telomeres or telomere-associated proteins. Abundant antisense mitochondrial transcripts (2% of all tags), suggest the existence of an antisense-mediated regulatory mechanism in C. elegans mitochondria. In addition to providing a robust tool for gene expression studies, the SAGE approach already has provided the advantage of new gene/transcript discovery in a metazoan.

Identification of new bone morphogenetic protein-related members in invertebrates

Although believed to be widely distributed among the animal kingdom, transforming growth factor-beta (TGF-beta) superfamily members have mainly been characterized in vertebrate and in invertebrate model organisms such as Drosophila and C. elegans. To characterize such new factors in invertebrates, a PCR screen was performed on genomic DNA from different animal phyla, using degenerate primers deduced from consensus sequences of known members of the TGF-beta superfamily. Four new members were identified from a cnidaria, an echinoderm and from two classes of molluscs. These new proteins exhibit a high degree of identity with human bone morphogenetic proteins (BMP2/4). Sequence comparisons suggest an early origin and an evolutionary conservation of the molecular conformation. However, their possible involvement in distinct regulatory pathways is discussed.

BIP, a BRAM-interacting protein involved in TGF-beta signalling, regulates body length in Caenorhabditis elegans

BACKGROUND

The TGF-beta superfamily has diverse biological activities and is involved in the early development of animals. We previously identified a novel family member, BMP receptor associated molecule (BRAM), which binds to the intracellular domain of BMP type IA receptor and is involved in the BMP signalling pathway.

RESULTS

To identify novel molecules involved in TGF-beta signalling pathways, we performed yeast two-hybrid screening using BRAM as bait. From a Xenopus cDNA library, we cloned a cDNA encoding 693 amino acids and containing the motif for an oxysterol binding protein (OSBP), which we designated BRAM interacting protein (BIP). We then isolated a BIP homologue from the Caenorhabditis elegans that encodes 733 amino acids and also contains the OSBP-like motif. Immunoprecipitation and Western blotting studies revealed that C. elegans BIP could interact with the C. elegans BRAM homologues BRA-1 and BRA-2. C. elegans BIP was expressed in pharyngeal muscle, hypodermis and several neuronal cells, an expression pattern overlaps with those of BRA-1 and BRA-2. Finally, we found that inhibition of BIP expression in C. elegans by double stranded RNA interference produces a Sma phenotype.

CONCLUSIONS

BIP was isolated using the yeast two-hybrid systems. BIP may function in the TGF-beta pathway and regulate body length in C. elegans.

Immunological genomics of Brugia malayi: filarial genes implicated in immune evasion and protective immunity

Filarial nematodes are metazoan parasites with genome sizes of> 100 million base pairs, probably encoding 15 000-20 000 genes. Within this considerable gene complement, it seems likely that filariae have evolved a spectrum of immune evasion products which underpin their ability to live for many years within the human host. Moreover, no suitable vaccine currently exists for human filarial diseases, and few markers have yet been established for diagnostic use. In this review, we bring together biochemical and immunological data on prominent filarial proteins with the exciting new information provided by the Filarial Genome Project's expressed sequence tag (EST) database. In this discussion, we focus on those genes with the highest immunological profile, such as inhibitors of host enzymes, cytokine homologues and stage-specific surface proteins, as well as products associated with the mosquito-borne infective larva which offer the best opportunity for an anti-filarial vaccine. These gene products provide a fascinating glimpse of the molecular repertoire which helminth parasites have evolved to manipulate and evade the mammalian immune response.

A DAF-1-binding protein BRA-1 is a negative regulator of DAF-7 TGF-beta signaling

We have identified homologs of a human BMP receptor-associated molecule BRAM1 in Caenorhabditis elegans. One of them, BRA-1, has been found to bind DAF-1, the type I receptor in the DAF-7 transforming growth factor-beta pathway through the conserved C-terminal region. As analyzed using a BRA-1GFP (green fluorescent protein) fusion gene product, the bra-1 gene is expressed in amphid neurons such as ASK, ASI, and ASG, where daf-1 is also expressed. A loss-of-function mutation in bra-1 exhibits robust suppression of the Daf-c phenotype caused by the DAF-7 pathway mutations. We propose that BRA-1 represents a novel class of receptor-associated molecules that negatively regulate transforming growth factor-beta pathways.