Comparative mechanistic study of RPE cell death induced by different oxidative stresses

Oxidative stress is hypothesized to drive the progression of age-related macular degeneration (AMD). Retinal pigment epithelial (RPE) cell layer is important for supporting the function of retina and is particularly susceptible to oxidative stress-induced cell death. How RPE cells die in AMD, especially in geographic atrophy (GA), a late stage of dry AMD, is still controversial. The goal of this study is to compare the features and mechanisms of RPE cell death induced by different oxidative stresses, to identify potential universal therapeutic targets for GA. RPE cell death was induced both in vitro and ex vivo by 4-Hydroxynonenal (4-HNE), a major product of lipid peroxidation, sodium iodate (NaIO3) that has been widely used to model RPE cell death in dry AMD, a ferroptosis inducer RAS-selective lethal 3 (RSL3) or a necroptosis inducer shikonin. We found that RPE necroptosis and ferroptosis show common and distinct features. Common features include receptor-interacting protein kinase (RIPK)1/RIPK3 activation and lipid reactive oxygen species (ROS) accumulation, although lipid ROS accumulation is much milder during necroptosis. This supports cross talk between RPE ferroptosis and necroptosis pathways and is consistent with the rescue of RPE necroptosis and ferroptosis by RIPK1 inhibitor Necrostatin-1 (Nec-1) or in Ripk3-/- RPE explants. Distinct feature includes activated mixed lineage kinase domain like pseudokinase (MLKL) that is translocated to the cell membrane during necroptosis, which is not happening in ferroptosis. This is consistent with the failure to rescue RPE ferroptosis by MLKL inhibitor necrosulfonamide (NSA) or in Mlkl-/- RPE explants. Using this framework, we found that 4-HNE and NaIO3 induced RPE cell death likely through necroptosis based on the molecular features and the rescuing effect by multiple inhibitors. Our studies suggest that multiple markers and inhibitors are required to distinguish RPE necroptosis and ferroptosis, and that necroptosis inhibitor Nec-1 could be a potential therapeutic compound for GA since it inhibits RIPK1/RIPK3 activation and lipid ROS accumulation occurred in both necroptosis and ferroptosis pathways.

Cytokine-Mediated Degradation of the Transcription Factor ERG Impacts the Pulmonary Vascular Response to Systemic Inflammatory Challenge

BACKGROUND

During infectious diseases, proinflammatory cytokines transiently destabilize interactions between adjacent vascular endothelial cells (ECs) to facilitate the passage of immune molecules and cells into tissues. However, in the lung, the resulting vascular hyperpermeability can lead to organ dysfunction. Previous work identified the transcription factor ERG (erythroblast transformation-specific-related gene) as a master regulator of endothelial homeostasis. Here we investigate whether the sensitivity of pulmonary blood vessels to cytokine-induced destabilization is due to organotypic mechanisms affecting the ability of endothelial ERG to protect lung ECs from inflammatory injury.

METHODS

Cytokine-dependent ubiquitination and proteasomal degradation of ERG were analyzed in cultured human umbilical vein ECs. Systemic administration of TNFα (tumor necrosis factor alpha) or the bacterial cell wall component lipopolysaccharide was used to cause a widespread inflammatory challenge in mice; ERG protein levels were assessed by immunoprecipitation, immunoblot, and immunofluorescence. Murine Erg deletion was genetically induced in ECs (Erg^fl/fl;Cdh5[PAC]-Cre^ERT2), and multiple organs were analyzed by histology, immunostaining, and electron microscopy.

RESULTS

In vitro, TNFα promoted the ubiquitination and degradation of ERG in human umbilical vein ECs, which was blocked by the proteasomal inhibitor MG132. In vivo, systemic administration of TNFα or lipopolysaccharide resulted in a rapid and substantial degradation of ERG within lung ECs but not ECs of the retina, heart, liver, or kidney. Pulmonary ERG was also downregulated in a murine model of influenza infection. Erg^fl/fl;Cdh5(PAC)-Cre^ERT2 mice spontaneously recapitulated aspects of inflammatory challenges, including lung-predominant vascular hyperpermeability, immune cell recruitment, and fibrosis. These phenotypes were associated with a lung-specific decrease in the expression of Tek-a gene target of ERG previously implicated in maintaining pulmonary vascular stability during inflammation.

CONCLUSIONS

Collectively, our data highlight a unique role for ERG in pulmonary vascular function. We propose that cytokine-induced ERG degradation and subsequent transcriptional changes in lung ECs play critical roles in the destabilization of pulmonary blood vessels during infectious diseases.

Cytokine-Mediated Degradation of the Transcription Factor ERG Impacts the Pulmonary Vascular Response to Systemic Inflammatory Challenge

Background

During infectious diseases, pro-inflammatory cytokines transiently destabilize interactions between adjacent vascular endothelial cells (ECs) to facilitate the passage of immune molecules and cells into tissues. However, in the lung the resulting vascular hyperpermeability can lead to organ dysfunction. Previous work identified the transcription factor ERG as a master regulator of endothelial homeostasis. Here we investigate whether the sensitivity of pulmonary blood vessels to cytokine-induced destabilization is due to organotypic mechanisms affecting the ability of endothelial ERG to protect lung ECs from inflammatory injury.

Methods

Cytokine-dependent ubiquitination and proteasomal degradation of ERG was analyzed in cultured Human Umbilical Vein ECs (HUVECs). Systemic administration of TNFα or the bacterial cell wall component lipopolysaccharide (LPS) was used to cause a widespread inflammatory challenge in mice; ERG protein levels were assessed by immunoprecipitation, immunoblot, and immunofluorescence. Murine Erg deletion was genetically induced in ECs ( Erg fl/fl ;Cdh5(PAC)Cre ERT2 ), and multiple organs were analyzed by histology, immunostaining, and electron microscopy.

Results

In vitro, TNFα promoted the ubiquitination and degradation of ERG in HUVECs, which was blocked by the proteasomal inhibitor MG132. In vivo, systemic administration of TNFα or LPS resulted in a rapid and substantial degradation of ERG within lung ECs, but not ECs of the retina, heart, liver, or kidney. Pulmonary ERG was also downregulated in a murine model of influenza infection. Erg fl/fl ;Cdh5(PAC)-Cre ERT2 mice spontaneously recapitulated aspects of inflammatory challenges, including lung-predominant vascular hyperpermeability, immune cell recruitment, and fibrosis. These phenotypes were associated with a lung-specific decrease in the expression of Tek , a gene target of ERG previously implicated in maintaining pulmonary vascular stability during inflammation.

Conclusions

Collectively, our data highlight a unique role for ERG in pulmonary vascular function. We propose that cytokine-induced ERG degradation and subsequent transcriptional changes in lung ECs play critical roles in the destabilization of pulmonary blood vessels during infectious diseases.

Mouse Chd4-NURD is required for neonatal spermatogonia survival and normal gonad development

Testis development and sustained germ cell production in adults rely on the establishment and maintenance of spermatogonia stem cells and their proper differentiation into spermatocytes. Chromatin remodeling complexes regulate critical processes during gamete development by restricting or promoting accessibility of DNA repair and gene expression machineries to the chromatin. Here, we investigated the role of Chd4 and Chd3 catalytic subunits of the NURD complex during spermatogenesis. Germ cell-specific deletion of chd4 early in gametogenesis, but not chd3, resulted in arrested early gamete development due to failed cell survival of neonate undifferentiated spermatogonia stem cell population. Candidate assessment revealed that Chd4 controls expression of dmrt1 and its downstream target plzf, both described as prominent regulators of spermatogonia stem cell maintenance. Our results show the requirement of Chd4 in mammalian gametogenesis pointing to functions in gene expression early in the process.

IL-1β Impacts Vascular Integrity and Lymphatic Function in the Embryonic Omentum

BACKGROUND

The chromatin-remodeling enzyme BRG1 (brahma-related gene 1) regulates gene expression in a variety of rapidly differentiating cells during embryonic development. However, the critical genes that BRG1 regulates during lymphatic vascular development are unknown.

METHODS

We used genetic and imaging techniques to define the role of BRG1 in murine embryonic lymphatic development, although this approach inadvertently expanded our study to multiple interacting cell types.

RESULTS

We found that omental macrophages fine-tune an unexpected developmental process by which erythrocytes escaping from naturally discontinuous omental blood vessels are collected by nearby lymphatic vessels. Our data indicate that circulating fibrin(ogen) leaking from gaps in omental blood vessels can trigger inflammasome-mediated IL-1β (interleukin-1β) production and secretion from nearby macrophages. IL-1β destabilizes adherens junctions in omental blood and lymphatic vessels, contributing to both extravasation of erythrocytes and their uptake by lymphatics. BRG1 regulates IL-1β production in omental macrophages by transcriptionally suppressing the inflammasome trigger RIPK3 (receptor interacting protein kinase 3).

CONCLUSIONS

Genetic deletion of Brg1 in embryonic macrophages leads to excessive IL-1β production, erythrocyte leakage from blood vessels, and blood-filled lymphatics in the developing omentum. Altogether, these results highlight a novel context for epigenetically regulated crosstalk between macrophages, blood vessels, and lymphatics.

Proinflammatory mediators, TNFα, IFNγ, and thrombin, directly induce lymphatic capillary tube regression

In this work, we sought to investigate the direct effects of proinflammatory mediators on lymphatic endothelial cell (LEC) capillaries and whether they might induce regression. Our laboratory has developed novel in-vitro, serum-free, lymphatic tubulogenesis assay models whereby human LEC tube networks readily form in either three-dimensional collagen or fibrin matrices. These systems were initially conceptualized in the hopes of better understanding the influence of proinflammatory mediators on LEC capillaries. In this work, we have screened and identified proinflammatory mediators that cause regression of LEC tube networks, the most potent of which is TNFα (tumor necrosis factor alpha), followed by IFNγ (interferon gamma) and thrombin. When these mediators were combined, even greater and more rapid lymphatic capillary regression occurred. Surprisingly, IL-1β (interleukin-1 beta), one of the most potent and pathologic cytokines known, had no regressive effect on these tube networks. Finally, we identified new pharmacological drug combinations capable of rescuing LEC capillaries from regression in response to the potent combination of TNFα, IFNγ, and thrombin. We speculate that protecting lymphatic capillaries from regression may be an important step toward mitigating a wide variety of acute and chronic disease states, as lymphatics are believed to clear both proinflammatory cells and mediators from inflamed and damaged tissue beds. Overall, these studies identify key proinflammatory mediators, including TNFα, IFNγ, and thrombin, that induce regression of LEC tube networks, as well as identify potential therapeutic agents to diminish LEC capillary regression responses.

Selective and Marked Blockade of Endothelial Sprouting Behavior Using Paclitaxel and Related Pharmacologic Agents

Whether alterations in the microtubule cytoskeleton affect the ability of endothelial cells (ECs) to sprout and form branching networks of tubes was investigated in this study. Bioassays of human EC tubulogenesis, where both sprouting behavior and lumen formation can be rigorously evaluated, were used to demonstrate that addition of the microtubule-stabilizing drugs, paclitaxel, docetaxel, ixabepilone, and epothilone B, completely interferes with EC tip cells and sprouting behavior, while allowing for EC lumen formation. In bioassays mimicking vasculogenesis using single or aggregated ECs, these drugs induce ring-like lumens from single cells or cyst-like spherical lumens from multicellular aggregates with no evidence of EC sprouting behavior. Remarkably, treatment of these cultures with a low dose of the microtubule-destabilizing drug, vinblastine, led to an identical result, with complete blockade of EC sprouting, but allowing for EC lumen formation. Administration of paclitaxel in vivo markedly interfered with angiogenic sprouting behavior in developing mouse retina, providing corroboration. These findings reveal novel biological activities for pharmacologic agents that are widely utilized in multidrug chemotherapeutic regimens for the treatment of human malignant cancers. Overall, this work demonstrates that manipulation of microtubule stability selectively interferes with the ability of ECs to sprout, a necessary step to initiate and form branched capillary tube networks.

Genomic locus proteomic screening identifies the NF-κB signaling pathway components NFκB1 and IKBKG as transcriptional regulators of Ripk3 in endothelial cells

The receptor-interacting protein kinase 3 (RIPK3) is a multi-functional protein best known for facilitating cellular necroptosis and inflammation. Recent evidence from our lab indicates that RIPK3 expression must be tightly regulated in endothelial cells to promote angiogenesis, to maintain vascular integrity during embryogenesis, and to provide protection from postnatal atherosclerosis. RIPK3 activity and stability are regulated by post-translational modifications and caspase-dependent cleavage. However, less is known about the transcriptional regulation of Ripk3. Here we utilized an unbiased CRISPR-based technology called genomic locus proteomics (GLoPro) to screen transcription factors and coregulatory proteins associated with the Ripk3 locus in a murine endothelial cell line. We found that 41 nuclear proteins are specifically enriched at the Ripk3 locus, including the Nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway components NFκB1 and IKBKG. We further verified that NFκB1 and IKBKG directly bind the Ripk3 promoter and prevent TNFα-induced Ripk3 transcription in cultured human primary endothelial cells. Moreover, NFκB1 prevents RIPK3-mediated death of primary endothelial cells. These data provide new insights into NF-κB signaling and Ripk3 transcriptional regulation in endothelial cells.

The chromatin-remodeling enzyme CHD3 plays a role in embryonic viability but is dispensable for early vascular development

ATP-dependent chromatin-remodeling complexes epigenetically modulate transcription of target genes to impact a variety of developmental processes. Our lab previously demonstrated that CHD4-a central ATPase and catalytic enzyme of the NuRD chromatin-remodeling complex-plays an important role in murine embryonic endothelial cells by transcriptionally regulating vascular integrity at midgestation. Since NuRD complexes can incorporate the ATPase CHD3 as an alternative to CHD4, we questioned whether the CHD3 enzyme likewise modulates vascular development or integrity. We generated a floxed allele of Chd3 but saw no evidence of lethality or vascular anomalies when we deleted it in embryonic endothelial cells in vivo (Chd3ECKO). Furthermore, double-deletion of Chd3 and Chd4 in embryonic endothelial cells (Chd3/4ECKO) did not dramatically alter the timing and severity of embryonic phenotypes seen in Chd4ECKO mutants, indicating that CHD3 does not play a cooperative role with CHD4 in early vascular development. However, excision of Chd3 at the epiblast stage of development with a Sox2-Cre line allowed us to generate global heterozygous Chd3 mice (Chd3Δ/+), which were subsequently intercrossed and revealed partial lethality of Chd3Δ/Δ mutants prior to weaning. Tissues from surviving Chd3Δ/Δ mutants helped us confirm that CHD3 was efficiently deleted in these animals and that CHD3 is highly expressed in the gonads and brains of adult wildtype mice. Therefore, Chd3-flox mice will be beneficial for future studies about roles for this chromatin-remodeling enzyme in viable embryonic development and in gonadal and brain physiology.

Cell-specific and athero-protective roles for RIPK3 in a murine model of atherosclerosis

Receptor-interacting protein kinase 3 (RIPK3) was recently implicated in promoting atherosclerosis progression through a proposed role in macrophage necroptosis. However, RIPK3 has been connected to numerous other cellular pathways, which raises questions about its actual role in atherosclerosis. Furthermore, RIPK3 is expressed in a multitude of cell types, suggesting that it may be physiologically relevant to more than just macrophages in atherosclerosis. In this study, Ripk3 was deleted in macrophages, endothelial cells, vascular smooth muscle cells or globally on the Apoe-/- background using Cre-lox technology. To induce atherosclerosis progression, male and female mice were fed a Western diet for three months before tissue collection and analysis. Surprisingly, necroptosis markers were nearly undetectable in atherosclerotic aortas. Furthermore, en face lesion area was increased in macrophage- and endothelial-specific deletions of Ripk3 in the descending and abdominal regions of the aorta. Analysis of bone-marrow-derived macrophages and cultured endothelial cells revealed that Ripk3 deletion promotes expression of monocyte chemoattractant protein 1 (MCP-1) and E-selectin in these cell types, respectively. Western blot analysis showed upregulation of MCP-1 in aortas with Ripk3-deficient macrophages. Altogether, these data suggest that RIPK3 in macrophages and endothelial cells protects against atherosclerosis through a mechanism that likely does not involve necroptosis. This protection may be due to RIPK3-mediated suppression of pro-inflammatory MCP-1 expression in macrophages and E-selectin expression in endothelial cells. These findings suggest a novel and unexpected cell-type specific and athero-protective function for RIPK3.This article has an associated First Person interview with the first author of the paper.

Proinflammatory Mediators, IL (Interleukin)-1β, TNF (Tumor Necrosis Factor) α, and Thrombin Directly Induce Capillary Tube Regression

OBJECTIVE

In this work, we examine the molecular basis for capillary tube regression and identify key proregressive factors, signaling pathways, and pharmacological antagonists of this process. Approach and Results: We demonstrate that the proinflammatory mediators, IL (interleukin)-1β, TNF (tumor necrosis factor) α, and thrombin, singly and in combination, are potent regulators of capillary tube regression in vitro. These proregressive factors, when added to endothelial cell-pericyte cocultures, led to selective loss of endothelial cell-lined tube networks, with retention and proliferation of pericytes despite the marked destruction of adjacent capillary tubes. Moreover, treatment of macrophages with the TLR (toll-like receptor) agonists Pam3CSK4 and lipopolysaccharide generates conditioned media with marked proregressive activity, that is completely blocked by a combination of neutralizing antibodies directed to IL-1β and TNFα but not to other factors. The same combination of blocking antibodies, as well as the anti-inflammatory cytokine IL-10, interfere with macrophage-dependent hyaloid vasculature regression in mice suggesting that proinflammatory cytokine signaling regulates capillary regression in vivo. In addition, we identified a capillary regression signaling signature in endothelial cells downstream of these proregressive agents that is characterized by increased levels of ICAM-1 (intercellular adhesion molecule-1), phospho-p38, and phospho-MLC2 (myosin light chain-2) and decreased levels of phospho-Pak2, acetylated tubulin, phospho-cofilin, and pro-caspase3. Finally, we identified combinations of pharmacological agents (ie, FIST and FISTSB) that markedly rescue the proregressive activities of IL-1β, TNFα, and thrombin, individually and in combination.

CONCLUSIONS

Overall, these new studies demonstrate that the major proinflammatory mediators, IL-1β, TNFα, and thrombin, are key regulators of capillary tube regression-a critical pathological process regulating human disease.

The NuRD chromatin-remodeling complex enzyme CHD4 prevents hypoxia-induced endothelial Ripk3 transcription and murine embryonic vascular rupture

Physiological hypoxia can trigger transcriptional events that influence many developmental processes during mammalian embryogenesis. One way that hypoxia affects transcription is by engaging chromatin-remodeling complexes. We now report that chromodomain helicase DNA binding protein 4 (CHD4), an enzyme belonging to the nucleosome remodeling and deacetylase (NuRD) chromatin-remodeling complex, is required for transcriptional repression of the receptor-interacting protein kinase 3 (Ripk3)-a critical executor of the necroptosis cell death program-in hypoxic murine embryonic endothelial cells. Genetic deletion of Chd4 in murine embryonic endothelial cells in vivo results in upregulation of Ripk3 transcripts and protein prior to vascular rupture and lethality at midgestation, and concomitant deletion of Ripk3 partially rescues these phenotypes. In addition, CHD4 binds to and prevents acetylation of the Ripk3 promoter in cultured endothelial cells grown under hypoxic conditions to prevent excessive Ripk3 transcription. These data demonstrate that excessive RIPK3 is detrimental to embryonic vascular integrity and indicate that CHD4 suppresses Ripk3 transcription when the embryonic environment is particularly hypoxic prior to the establishment of fetal-placental circulation at midgestation. Altogether, this research provides new insights into regulators of Ripk3 transcription and encourages future studies into the mechanism by which excessive RIPK3 damages embryonic blood vessels.

Characterizing Epigenetic Changes in Endothelial Cells

Chromatin immunoprecipitation (ChIP) is an antibody-based method used to identify protein-DNA interactions and sites of protein modifications to chromatin in living cells. ChIP is a powerful method for identifying genomic sites at which epigenetic changes occur in cell types of interest because many antibodies have been developed that recognize specific epigenetic modifications of histone tails. This chapter provides detailed ChIP and subsequent polymerase chain reaction (ChIP-PCR) protocols for use in cultured endothelial cells. These protocols will allow investigators to make consistent and quantitative discoveries about epigenetic changes that occur in endothelial cells at specific genomic sites under varying treatment conditions.

Excessive Plasmin Compromises Hepatic Sinusoidal Vascular Integrity After Acetaminophen Overdose

The serine protease plasmin degrades extracellular matrix (ECM) components both directly and indirectly through activation of matrix metalloproteinases. Excessive plasmin activity and subsequent ECM degradation cause hepatic sinusoidal fragility and hemorrhage in developing embryos. We report here that excessive plasmin activity in a murine acetaminophen (APAP) overdose model likewise compromises hepatic sinusoidal vascular integrity in adult animals. We found that hepatic plasmin activity is up-regulated significantly at 6 hours after APAP overdose. This plasmin up-regulation precedes both degradation of the ECM component fibronectin around liver vasculature and bleeding from centrilobular sinusoids. Importantly, administration of the pharmacological plasmin inhibitor tranexamic acid or genetic reduction of plasminogen, the circulating zymogen of plasmin, ameliorates APAP-induced hepatic fibronectin degradation and sinusoidal bleeding. Conclusion: These studies demonstrate that reduction of plasmin stabilizes hepatic sinusoidal vascular integrity after APAP overdose. (Hepatology 2018; 00:1-13).

BRG1 (Brahma-Related Gene 1) Promotes Endothelial Mrtf Transcription to Establish Embryonic Capillary Integrity

OBJECTIVE

The chromatin remodeling enzyme BRG1 (brahma-related gene 1) transcriptionally regulates target genes important for early blood vessel development and primitive hematopoiesis. However, because Brg1 deletion in vascular progenitor cells results in lethal anemia by embryonic day 10.5 (E10.5), roles for BRG1 in embryonic vascular development after midgestation are unknown. In this study, we sought to determine whether endothelial cell BRG1 regulates genes important for vascular development or maintenance later in embryonic development.

APPROACH AND RESULTS

Using mice with temporally inducible deletion of endothelial BRG1 (Brg1^fl/fl;Cdh5(PAC)-Cre^ERT2 ), we found that Brg1 excision between E9.5 and 11.5 results in capillary dilation and lethal hemorrhage by E14.5. This phenotype strongly resembles that seen when the SRF (serum response factor) transcription factor is deleted from embryonic endothelial cells. Although expression of Srf and several of its known endothelial cell target genes are downregulated in BRG1-depleted endothelial cells, we did not detect binding of BRG1 at these gene promoters, indicating that they are not direct BRG1 target genes. Instead, we found that BRG1 binds to the promoters of the SRF cofactors Mrtfa and Mrtfb (myocardin-related transcription factors A and B) in endothelial cells, and these genes are downregulated in Brg1-deficient endothelial cells.

CONCLUSIONS

BRG1 promotes transcription of endothelial Mrtfa and Mrtfb, which elevates expression of SRF and SRF target genes that establish embryonic capillary integrity. These data highlight a new and temporally specific role for BRG1 in embryonic vasculature and provide novel information about epigenetic regulation of Mrtf expression and SRF signaling in developing blood vessels.

Building discontinuous liver sinusoidal vessels

Blood vessels have a unified mission to circulate blood throughout the body; however, they have additional diverse and specialized roles in various organs. For example, in the liver, discontinuous sinusoids, which are fenestrated capillaries with intercellular gaps and a fragmented basement membrane, facilitate delivery of macromolecules to highly metabolic hepatocytes. During embryonic development, discontinuous sinusoids also allow circulating hematopoietic progenitor and stem cells to populate the liver and promote blood cell differentiation. In this issue of the JCI, Géraud et al. describe an essential role for the transcription factor GATA4 in promoting the development of discontinuous sinusoids. In the absence of liver sinusoidal GATA4, mouse embryos developed hepatic capillaries with upregulated endothelial cell junction proteins and a continuous basement membrane. These features prevented hematopoietic progenitor cells from transmigrating into the developing liver, and Gata4-mutant embryos died from subsequent liver hypoplasia and anemia. This study highlights the surprising and extensive transcriptional control GATA4 exercises over specialized liver vascular development and function.

CHD4-regulated plasmin activation impacts lymphovenous hemostasis and hepatic vascular integrity

The chromatin-remodeling enzyme CHD4 maintains vascular integrity at mid-gestation; however, it is unknown whether this enzyme contributes to later blood vessel or lymphatic vessel development. Here, we addressed this issue in mice harboring a deletion of Chd4 specifically in cells that express lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1), which include lymphatic endothelial cells (LECs) and liver sinusoidal endothelial cells. Chd4 mutant embryos died before birth and exhibited severe edema, blood-filled lymphatics, and liver hemorrhage. CHD4-deficient embryos developed normal lymphovenous (LV) valves, which regulate the return of lymph to the blood circulation; however, these valves lacked the fibrin-rich thrombi that prevent blood from entering the lymphatic system. Transcripts of the urokinase plasminogen activator receptor (uPAR), which facilitates activation of the fibrin-degrading protease plasmin, were upregulated in Chd4 mutant LYVE1+ cells, and plasmin activity was elevated near the LV valves. Genetic reduction of the uPAR ligand urokinase prevented degradation of fibrin-rich thrombi at the LV valves and largely resolved the blood-filled lymphatics in Chd4 mutants. Urokinase reduction also ameliorated liver hemorrhage and prolonged embryonic survival by reducing plasmin-mediated extracellular matrix degradation around sinusoidal blood vessels. These results highlight the susceptibility of LV thrombi and liver sinusoidal vessels to plasmin-mediated damage and demonstrate the importance of CHD4 in regulating embryonic plasmin activation after mid-gestation.

Higher relatedness mitigates mortality in a nematode with lethal male fighting

According to kin selection theory, individuals show less aggression towards their relatives. Limited dispersal promotes interactions among relatives but also increases competition among them. The evolution of cooperation in viscous populations has been subject of mainly theoretical exploration. We investigated the influence of relatedness on aggression in males of entomopathogenic nematode Steinernema longicaudum that engage in lethal fighting. In a series of in vitro experiments, we found that both competitor male group size and relatedness influence male mortality rates. Higher relatedness led to progressively lower rates of male mortality. In experimentally infected insects, wherein large numbers of males and females interact, the proportion of dead and paralysed (= terminally injured) males was higher when infection was established by infective juveniles originating from a mixture of three lines than in those infected by a single line. The results collectively show that Steinernema longicaudum males recognize their kin and consequently male mortality rates are lower in groups consisting of more related males. Furthermore, this monotonic negative relationship between aggression and relatedness suggests that kin selection benefits are still substantial even under extreme competition. Our experiments also suggest that kin recognition in entomopathogenic nematodes has a genetic basis rather than being strictly based on environmental cues. We discuss our findings within the theoretical context of the evolution of altruistic/cooperative behaviour in structured populations.

SWI/SNF chromatin-remodeling enzymes Brahma-related gene 1 (BRG1) and Brahma (BRM) are dispensable in multiple models of postnatal angiogenesis but are required for vascular integrity in infant mice

Background

Mammalian SWItch/Sucrose NonFermentable (SWI/SNF) adenosine triphosphate (ATP)‐dependent chromatin‐remodeling complexes play important roles in embryonic vascular development by modulating transcription of specific target genes. We sought to determine whether SWI/SNF complexes likewise impact postnatal physiological and pathological angiogenesis.

Methods and Results

Brahma‐related gene 1 (BRG1) and Brahma gene (BRM) are ATPases within mammalian SWI/SNF complexes and are essential for the complexes to function. Using mice with vascular‐specific mutations in Brg1 or with a global mutation in Brm, we employed 3 models to test the role of these ATPases in postnatal angiogenesis. We analyzed neonatal retinal angiogenesis, exercise‐induced angiogenesis in adult quadriceps muscles, and tumor angiogenesis in control and mutant animals. We found no evidence of defective angiogenesis in Brg1 or Brm mutants using these 3 models. Brg1/Brm double mutants likewise show no evidence of vascular defects in the neonatal retina or tumor angiogenesis models. However, 100% of Brg1/Brm‐double mutants in which Brg1 deletion is induced at postnatal day 3 (P3) die by P19 with hemorrhaging in the small intestine and heart.

Conclusions

Despite their important roles in embryonic vascular development, SWI/SNF chromatin‐remodeling complexes display a surprising lack of participation in the 3 models of postnatal angiogenesis we analyzed. However, these complexes are essential for maintaining vascular integrity in specific tissue beds before weaning. These findings highlight the temporal and spatial specificity of SWI/SNF activities in the vasculature and may indicate that other chromatin‐remodeling complexes play redundant or more essential roles during physiological and pathological postnatal vascular development.

The NuRD chromatin-remodeling enzyme CHD4 promotes embryonic vascular integrity by transcriptionally regulating extracellular matrix proteolysis

The extracellular matrix (ECM) supports vascular integrity during embryonic development. Proteolytic degradation of ECM components is required for angiogenesis, but excessive ECM proteolysis causes blood vessel fragility and hemorrhage. Little is understood about how ECM proteolysis is transcriptionally regulated during embryonic vascular development. We now show that the NuRD ATP-dependent chromatin-remodeling complex promotes vascular integrity by preventing excessive ECM proteolysis in vivo. Mice lacking endothelial CHD4--a catalytic subunit of NuRD complexes--died at midgestation from vascular rupture. ECM components surrounding rupture-prone vessels in Chd4 mutants were significantly downregulated prior to embryonic lethality. Using qPCR arrays, we found two critical mediators of ECM stability misregulated in mutant endothelial cells: the urokinase-type plasminogen activator receptor (uPAR or Plaur) was upregulated, and thrombospondin-1 (Thbs1) was downregulated. Chromatin immunoprecipitation assays showed that CHD4-containing NuRD complexes directly bound the promoters of these genes in endothelial cells. uPAR and THBS1 respectively promote and inhibit activation of the potent ECM protease plasmin, and we detected increased plasmin activity around rupture-prone vessels in Chd4 mutants. We rescued ECM components and vascular rupture in Chd4 mutants by genetically reducing urokinase (uPA or Plau), which cooperates with uPAR to activate plasmin. Our findings provide a novel mechanism by which a chromatin-remodeling enzyme regulates ECM stability to maintain vascular integrity during embryonic development.

BRG1 promotes COUP-TFII expression and venous specification during embryonic vascular development

Arteries and veins acquire distinct molecular identities prior to the onset of embryonic blood circulation, and their specification is crucial for vascular development. The transcription factor COUP-TFII currently functions at the top of a signaling pathway governing venous fate. It promotes venous identity by inhibiting Notch signaling and subsequent arterialization of endothelial cells, yet nothing is known about what regulates COUP-TFII expression in veins. We now report that the chromatin-remodeling enzyme BRG1 promotes COUP-TFII expression in venous endothelial cells during murine embryonic development. Conditional deletion of Brg1 from vascular endothelial cells resulted in downregulated COUP-TFII expression and aberrant expression of arterial markers on veins. BRG1 promotes COUP-TFII expression by binding conserved regulatory elements within the COUP-TFII promoter and remodeling chromatin to make the promoter accessible to transcriptional machinery. This study provides the first description of a factor promoting COUP-TFII expression in vascular endothelium and highlights a novel role for chromatin remodeling in venous specification.

Simulated roots and host feeding enhance infection of subterranean insects by the entomopathogenic nematode Steinernema carpocapsae

Steinernema carpocapsae can be effective against root-feeding insects despite its reputation as a sedentary ambusher. In pot experiments, using twigs as surrogate roots and pine weevil larvae as targets, we tested the hypothesis that roots serve as physical routeways and conduits of feeding-associated stimuli, thus enhancing the success of S. carpocapsae applied at the surface against subterranean hosts. Insect mortality was lowest (25%) in the absence of plant material, increased to 48% when twigs linked nematodes and insects, and further increased to 69% when the insects were allowed feed on the twigs. This is the first experimental support for the root-routeway hypothesis.

Competition and intraguild predation between the braconid parasitoid Bracon hylobii and the entomopathogenic nematode Heterorhabditis downesi, natural enemies of the large pine weevil, Hylobius abietis

In biological control programmes introduced natural enemies compete with indigenous enemies for hosts and may also engage in intraguild predation when two species competing for the same prey attack and consume one another. The large pine weevil, Hylobius abietis L. (Coleoptera: Curculionidae), is an important pest of coniferous reforestation in Europe. Among its natural enemies, the parasitoid Bracon hylobii Ratz. (Hymenoptera: Braconidae) and entomopathogenic nematodes have potential as biological control agents. Both parasitoid and nematodes target the weevil larvae and, hence, there is potential for competition or intraguild predation.In this study, we examine the interaction of B. hylobii with the nematode Heterorhabditis downesi Stock, Griffin and Burnell (Nematode: Heterorhabditidae), testing the susceptibility of larvae, pupae and adults of B. hylobii to H. downesi and whether female parasitoids discriminate between nematode-infected and uninfected weevils for oviposition. In choice tests, when weevils were exposed to nematodes 1-7 days previously, no B. hylobii oviposited on nematode-infected weevil larvae. Up to 24 h, healthy weevils were twice as likely as nematode-infected ones to be used for oviposition. Bracon hylobii females did not adjust clutch size; nematode-infected hosts were either rejected or the parasitoid laid a full clutch of eggs on them.When nematodes were applied to the parasitoid feeding on weevil larvae, the nematodes parasitized the parasitoid larvae, there was a reduction in cocoon formation and fewer cocoons eclosed. Eclosion rate was not reduced when nematodes were applied to fully formed cocoons, but nearly all of the emerging adults were killed by nematodes.

Establishment, persistence, and introgression of entomopathogenic nematodes in a forest ecosystem

Entomopathogenic nematodes (EPN) are currently marketed worldwide for use in inundative biological control, where the applied natural enemy population (rather than its offspring) is expected to reduce insect numbers. Unlike classical biological control, in inundative control natural enemy establishment is not crucial in order to achieve pest suppression. Field trials in Irish forestry provided the opportunity to test predictions regarding the establishment of two exotic (Steinernema carpocapsae and Heterorhabditis megidis) and two indigenous (Steinernema feltiae and Heterorhabditis downesi) species. Nematodes were inundatively applied to pine stumps to control populations of pine weevil, Hylobius abietis, on three clearcut sites, and their persistence and spread monitored for up to five years. All species were recovered three years after application but only S. feltiae was recovered in years 4 and 5. Limited horizontal dispersal to 20 cm (but not 100 cm) was observed, but the majority of nematodes were recovered close to the area of application. Steinernema feltiae was also recovered from nearby stumps to which it had not been applied, indicating possible phoretic dispersal by weevils or other stump-associated fauna. EPN were not recovered from stumps outside the treated area, suggesting that such dispersal is quite localized. Two strains of S. feltiae (Irish and exotic) were applied. Amplified fragment length polymorphism (AFLP) analysis on 11 populations isolated from soil four years later showed that all had a much closer affinity to the applied Irish strain, suggesting persistence of this genotype and extinction of the exotic one. Some strains were clustered close together, and this is interpreted in the light of possible population genetic scenarios. The findings from the field study confirm predictions based on background knowledge of the species and demonstrate the importance of medium-term studies, as a 3-year study would have overestimated the risk of establishment of exotic species. Short-term persistence and spread of S. carpocapsae, S. feltiae, and H. downesi was also studied in pine forest mesocosms. Similar trends to field results, such as limited horizontal dispersal, even vertical distribution, and more abundant recovery of S. feltiae than of other species, point to the utility of mesocosm studies as a predictive tool.

The chromatin-remodeling enzyme BRG1 plays an essential role in primitive erythropoiesis and vascular development

ATP-dependent chromatin-remodeling complexes contribute to the proper temporal and spatial patterns of gene expression in mammalian embryos and therefore play important roles in a number of developmental processes. SWI/SNF-like chromatin-remodeling complexes use one of two different ATPases as their catalytic subunit: brahma (BRM, also known as SMARCA2) and brahma-related gene 1 (BRG1, also known as SMARCA4). We have conditionally deleted a floxed Brg1 allele with a Tie2-Cre transgene, which is expressed in developing hematopoietic and endothelial cells. Brg1(fl/fl):Tie2-Cre(+) embryos die at midgestation from anemia, as mutant primitive erythrocytes fail to transcribe embryonic alpha- and beta-globins, and subsequently undergo apoptosis. Additionally, vascular remodeling of the extraembryonic yolk sac is abnormal in Brg1(fl/fl):Tie2-Cre(+) embryos. Importantly, Brm deficiency does not exacerbate the erythropoietic or vascular abnormalities found in Brg1(fl/fl):Tie2-Cre(+) embryos, implying that Brg1-containing SWI/SNF-like complexes, rather than Brm-containing complexes, play a crucial role in primitive erythropoiesis and in early vascular development.

Emergence and Dispersal Patterns of Two Isolates of the Entomopathogenic Nematode Steinernema feltiae

Few studies have addressed the role of the sexes in the emergence and dispersal of entomopathogenic nematodes from host insects. Individuals of two isolates of Steinernema feltiae, UK76 and SBIl, emerging from Galleria mellonella cadavers were classed as Non-Dispersed (remaining on the cadaver for up to nine days) and Dispersed (actively moving away from the cadaver). Sex ratios within both classes were examined in infective (individuals that successfully invaded bait G. mellonella) and entire (infective and noninfective individuals that matured in hanging drops of G. mellonella haemolymph) populations. Sex ratios differed significantly from 1:1 only in the SBIl Non-Dispersed entire population (female bias) and SBIl Non-Dispersed infective population (male bias). For each isolate, Dispersed individuals were significantly more infective than Non-Dispersed. However, only 11% of SBIl and 22% of UK76 Non-Dispersed individuals were found to be mature infective juveniles (IJ) compared with 78% of SBIl and 82% of UK76 Dispersed individuals (based on survival in SDS). Infective juveniles dispersing towards distant radial bait G. mellonella tended to migrate from the head region of the natal cadaver. For each isolate, a higher proportion of males than females arrived early at distant baits. SBIl males survived alone in G. mellonella cadavers for longer periods than did females, which supports the "male colonization" hypothesis.

An essential role for SNX1 in lysosomal sorting of protease-activated receptor-1: evidence for retromer-, Hrs-, and Tsg101-independent functions of sorting nexins

Sorting nexin 1 (SNX1) and SNX2 are the mammalian homologues of the yeast Vps5p retromer component that functions in endosome-to-Golgi trafficking. SNX1 is also implicated in endosome-to-lysosome sorting of cell surface receptors, although its requirement in this process remains to be determined. To assess SNX1 function in endocytic sorting of protease-activated receptor-1 (PAR1), we used siRNA to deplete HeLa cells of endogenous SNX1 protein. PAR1, a G-protein-coupled receptor, is proteolytically activated by thrombin, internalized, sorted predominantly to lysosomes, and efficiently degraded. Strikingly, depletion of endogenous SNX1 by siRNA markedly inhibited agonist-induced PAR1 degradation, whereas expression of a SNX1 siRNA-resistant mutant protein restored agonist-promoted PAR1 degradation in cells lacking endogenous SNX1, indicating that SNX1 is necessary for lysosomal degradation of PAR1. SNX1 is known to interact with components of the mammalian retromer complex and Hrs, an early endosomal membrane-associated protein. However, activated PAR1 degradation was not affected in cells depleted of retromer Vps26/Vps35 subunits, Hrs or Tsg101, an Hrs-interacting protein. We further show that SNX2, which dimerizes with SNX1, is not essential for lysosomal sorting of PAR1, but rather can regulate PAR1 degradation by disrupting endosomal localization of endogenous SNX1 when ectopically expressed. Together, our findings establish an essential role for endogenous SNX1 in sorting activated PAR1 to a distinct lysosomal degradative pathway that is independent of retromer, Hrs, and Tsg101.

Genetic evidence for a mammalian retromer complex containing sorting nexins 1 and 2

We have previously shown that the putative mammalian retromer components sorting nexins 1 and 2 (Snx1 and Snx2) result in embryonic lethality when simultaneously targeted for deletion in mice, whereas others have shown that Hbeta58 (also known as mVps26), another retromer component, results in similar lethality when targeted for deletion. In the current study, we address the genetic interaction of these mammalian retromer components in mice. Our findings reveal a functional interaction between Hbeta58, SNX1, and SNX2 and strongly suggest that SNX2 plays a more critical role than SNX1 in retromer activity during embryonic development. This genetic evidence supports the existence of mammalian retromer complexes containing SNX1 and SNX2 and identifies SNX2 as an important mediator of retromer biology. Moreover, we find that mammalian retromer complexes containing SNX1 and SNX2 have an essential role in embryonic development that is independent of cation-independent mannose 6-phosphate receptor trafficking.

Role of CD44 in Epithelial Wound Repair

The hyaluronic acid receptor, CD44, exists as multiple splice variants that appear to have a role in migration of tumor cells. The role of this receptor and its variants in normal wound repair is poorly understood. A central feature of wound repair in the liver is activation and migration of perisinusoidal stellate cells. We have examined CD44 expression by stellate cells from normal or injured rat liver, finding that it increases with injury and involves a distinct set of CD44 splice variants. Among the latter, variants containing the v6 exon (CD44v6) are strikingly increased. Analysis of migration of primary cells on transwell filter inserts reveals that only cells isolated from injured liver are migratory. Also, they move more rapidly on hyaluronic acid than on collagen I or collagen IV. A polyclonal antibody to recombinant CD44v6 blocks migration by 50%, whereas antibody to CD44v4 has no effect. The inhibition is specific for cells migrating on hyaluronic acid and is reversed by synthetic peptide representing the N terminus of the v6 protein. In conclusion, activated stellate cells use CD44v6 and hyaluronic acid for migration. Given the evidence that migration is required for progression of injury with scar formation, blockers of CD44v6 expression or function are candidates for preventing the deleterious effects of chronic fibrosis.

Specificity of association between Paenibacillus spp. and the entomopathogenic nematodes, Heterorhabditis spp

Endospore-forming bacteria, Paenibacillus spp., have recently been isolated in association with insect pathogenic nematodes Heterorhabditis spp. Sporangia adhere to nematode infective juveniles (J3) and are carried with them into insects. Paenibacillus proliferates in the killed insect along with Heterorhabditis and its obligate bacterial symbiont, Photorhabdus, despite the antibiotic production of the latter. Nematode infective juveniles leave the insect cadaver with Paenibacillus sporangia attached. The specificity of the relationship between Paenibacillus and Heterorhabditis was investigated. Sporangia of nematode-associated Paenibacillus adhered to infective juveniles (but not other stages) of all Heterorhabditis species tested, and to infective juveniles of vertebrate parasitic Strongylida species, but not to a variety of other soil nematodes tested. Paenibacillus species that were not isolated from nematodes, but were phylogenetically close to the nematode-associated strains, did not adhere to Heterorhabditis, and they were also sensitive to Photorhabdus antibiotics in vitro, whereas the nematode-associated strains were not. Unusual longevity of the sporangium and resistance to Photorhabdus antibiotics may represent specific adaptations of the nematode-associated Paenibacillus strains to allow them to coexist with and be transported by Heterorhabditis. Adaptation to specific Heterorhabditis-Photorhabdus strains is evident among the three nematode-associated Paenibacillus strains (each from a different nematode strain). Paenibacillus NEM1a and NEM3 each developed best in cadavers with the nematode from which it was isolated and not at all with the nematode associate of the other strain. Differences between nematode-associated Paenibacillus strains in cross-compatibility with the various Heterorhabditis strains in cadavers could not be explained by differential sensitivity to antibiotics produced by the nematodes' Photorhabdus symbionts in vitro.

A role for sorting nexin 2 in epidermal growth factor receptor down-regulation: evidence for distinct functions of sorting nexin 1 and 2 in protein trafficking

Sorting nexin 1 (SNX1) and SNX2, homologues of the yeast vacuolar protein-sorting (Vps)5p, contain a phospholipid-binding motif termed the phox homology (PX) domain and a carboxyl terminal coiled-coil region. A role for SNX1 in trafficking of cell surface receptors from endosomes to lysosomes has been proposed; however, the function of SNX2 remains unknown. Toward understanding the function of SNX2, we first examined the distribution of endogenous protein in HeLa cells. We show that SNX2 resides primarily in early endosomes, whereas SNX1 is found partially in early endosomes and in tubulovesicular-like structures distributed throughout the cytoplasm. We also demonstrate that SNX1 interacts with the mammalian retromer complex through its amino terminal domain, whereas SNX2 does not. Moreover, activated endogenous epidermal growth factor receptor (EGFR) colocalizes markedly with SNX2-positive endosomes, but minimally with SNX1-containing vesicles. To assess SNX2 function, we examined the effect of a PX domain-mutated SNX2 that is defective in vesicle localization on EGFR trafficking. Mutant SNX2 markedly inhibited agonist-induced EGFR degradation, whereas internalization remained intact. In contrast, SNX1 PX domain mutants failed to effect EGFR degradation, whereas a SNX1 deletion mutant significantly inhibited receptor down-regulation. Interestingly, knockdown of SNX1 and SNX2 expression by RNA interference failed to alter agonist-induced EGFR down-regulation. Together, these findings suggest that both SNX1 and SNX2 are involved in regulating lysosomal sorting of internalized EGFR, but neither protein is essential for this process. These studies are the first to demonstrate a function for SNX2 in protein trafficking.

Phased infectivity in Heterorhabditis megidis: the effects of infection density in the parental host and filial generation

Entomopathogenic nematodes can develop through two or more generations in the cadavers of killed insect hosts. Non-feeding infective juveniles from each generation emerge and may spend prolonged periods searching for a new host. The infectivity of the infective juveniles of Heterorhabditis megidis varies with time after emergence and may not reach a maximum until several weeks have passed. 'Phased infectivity' hypotheses propose that this pattern is adaptive, tending to reduce competition in new hosts. Here we provide further evidence that infectivity is phased in H. megidis. In addition, we show that the basic pattern is modified by infection density in the parental host and by filial generation. Two general patterns were observed: first, infective juveniles that developed under the least crowded conditions (F(1) infective juveniles produced in hosts infected with 16 parent nematodes) reached maximum infectivity after only 15 days, compared to 27 or 39 days for infective juveniles that developed under more crowded conditions (F(1) produced in hosts infected with 103 or 424 parent nematodes or F(2) infective juveniles). Second, infective juveniles had lower infectivity overall when produced under the most crowded conditions (F(2) versus F(1); highest versus lowest infection density). We propose that while lower overall infectivity is a necessary consequence of limited resource availability during infective juvenile development, the difference in the timing of peak infectivity reflects a shift in the fitness gains associated with being maximally infective either 'early' or 'late'. F(1) infective juveniles emerge several days before F(2) infective juveniles, and we suggest that filial generation and infection density in the parental host function as indicators of the potential risk of competition within new hosts.

Genetic analysis of sorting nexins 1 and 2 reveals a redundant and essential function in mice

Sorting nexins 1 (Snx1) and 2 (Snx2) are homologues of the yeast gene VPS5 that is required for proper endosome-to-Golgi trafficking. The prevailing thought is that Vps5p is a component of a retrograde trafficking complex called the retromer. Genetic and biochemical evidence suggest mammals may have similar complexes, but their biological role is unknown. Furthermore, if SNX1 and SNX2 belong to such complexes, it is not known whether they act together or separately. Herein, we show that mice lacking SNX1 or SNX2 are viable and fertile, whereas embryos deficient in both proteins arrest at midgestation. These results demonstrate that SNX1 and SNX2 have a highly redundant and necessary function in the mouse. The phenotype of Snx1(-/-);Snx2(-/-) embryos is very similar to that of embryos lacking another retromer homologue, Hbeta58. This finding suggests that SNX1/SNX2 and Hbeta58 function in the same genetic pathway, providing additional evidence for the existence of mammalian complexes that are structurally similar to the yeast retromer. Furthermore, the viability of Snx1(-/-) and Snx2(-/-) mice demonstrates that it is not necessary for SNX1 and SNX2 to act together. Electron microscopy indicates morphological alterations of apical intracellular compartments in the Snx1(-/-);Snx2(-/-) yolk-sac visceral endoderm, suggesting SNX1 and SNX2 may be required for proper cellular trafficking. However, tetraploid aggregation experiments suggest that yolk sac defects cannot fully account for Snx1(-/-); Snx2(-/-) embryonic lethality. Furthermore, endocytosis of transferrin and low-density lipoprotein is unaffected in mutant primary embryonic fibroblasts, indicating that SNX1 and SNX2 are not essential for endocytosis in all cells. Although the two proteins demonstrate functional redundancy, Snx1(+/-);Snx2(-/-) mice display abnormalities not observed in Snx1(-/-);Snx2(+/-) mice, revealing that SNX1 and SNX2, or their genetic regulation, are not equivalent. Significantly, these studies represent the first mutations in the mammalian sorting nexin gene family and indicate that sorting nexins perform essential functions in mammals.

Density-dependent fecundity and infective juvenile production in the entomopathogenic nematode, Heterorhabditis megidis

The entomopathogenic nematode Heterorhabditis megidis may undergo several rounds of reproduction within a single host. Infective juveniles (IJs) are formed within each generation during a process referred to as endotokia matricida, which involves the progressive consumption of the parent hermaphrodite or female by the developing IJs prior to emergence from the host cadaver. The present study examines the extent to which within-host population dynamics exhibit density-dependent variation. Particular attention is paid to the effect of infection density on the relative production of IJs and 'normal', non-infective offspring within each generation and on the emergence of the IJs from the host. Fecundity was found to be negatively density dependent across generations. However, at high infection density the first generation hermaphrodites invested relatively more in IJs at the expense of producing non-infective offspring. It is suggested that this pattern resulted from an adaptive, phenotypically plastic allocation of reproductive investment between offspring types in response to increased competition. The F1 and F2 IJs were also shown to emerge from the host in relatively discrete pulses.

Persistence of four heterorhabditis spp. isolates in soil: role of lipid reserves

Infective juveniles of four Heterorhabditis isolates (H. bacteriophora HI, H. megidis UK211 and HF85, and H. downesi M245) were stored in moist (pF 1.7) and dry (pF 3.3) loam soil at 20 degrees C for up to 141 days. Survival, assessed by the number of nematodes extracted by centrifugal flotation, declined over time, reaching fewer than 18% alive by day 141 for all but one treatment (H. bacteriophora HI in dry soil). The infectivity of nematodes in soil for Tenebrio molitor also declined over time, roughly in accordance with the decline in numbers of nematodes. Energy reserves of extracted nematodes were assessed by image analysis densitometry. There were differences among isolates both in survival and in the depletion of reserves, and there was a significant correlation between these two parameters, suggesting that the extent to which energy reserves are depleted affects survival or that a common factor influences both. However, significant nematode mortality occurred while levels of reserves remained high, and the maximum reduction in utilizable body content for any treatment was 51%, well above starvation level. Therefore, the decline in numbers of living nematodes and the reduced nematode infectivity in soil cannot directly result from starvation of the nematodes. Survival and infectivity declined more rapidly in moist than in dry soil; one isolate, H. downesi M245, was less affected by soil moisture content than the other three isolates.

Phased activity in Heterorhabditis megidis infective juveniles

The infectivity of Heterorhabditis megidis infective juveniles (IJs) increases during storage in water. We investigated whether this change can be related to other features of the IJs' behaviour. IJs were stored in water for 4 weeks at 20 degrees C, and the following parameters were assessed at intervals: infectivity for Galleria mellonella, dispersal in sand, host-finding on agar, and the percentage of IJs active in water. In addition, the behaviour of the IJs in water was described using 7 categories. Immediately after emerging from the host cadaver, IJs were highly active (99% of IJs in water were active and 65% displayed 'waving', the normal method of forward movement). Maximum responsiveness to host volatiles in an agar plate assay was recorded on day 2 (69% of IJs moved from the point of application and 44% of all IJs in the agar arena moved towards a host) and maximum dispersal in sand (5.8 cm) on day 0. These tendencies declined gradually with age, while infectivity underwent a significant increase from 11 nematodes per insect on day 0 to 38 nematodes per insect on day 9. Three phases could be distinguished in the behaviour of H. megidis IJs: an initial dispersal phase, during which infectivity was low; an infective phase, during which dispersal tendency was declining, and a third phase during which all behaviours (dispersal, infectivity and activity) were declining. Over the 4-week storage period, infectivity of H. megidis IJs was correlated (R2 = 0.83) with the percentage time IJs engaged in 'head thrusting' (a behaviour that resembles penetration). There is no evidence that the observed increase in infectivity of H. megidis strain UK211 could be accounted for by a generally greater level of motor activity, nor by an increase in responsiveness to volatile host cues, and it is suggested that it is due to an increased tendency to attempt penetration.

A role for thrombin receptor signaling in endothelial cells during embryonic development

The coagulation protease thrombin triggers fibrin formation, platelet activation, and other cellular responses at sites of tissue injury. We report a role for PAR1, a protease-activated G protein-coupled receptor for thrombin, in embryonic development. Approximately half of Par1-/- mouse embryos died at midgestation with bleeding from multiple sites. PAR1 is expressed in endothelial cells, and a PAR1 transgene driven by an endothelial-specific promoter prevented death of Par1-/- embryos. Our results suggest that the coagulation cascade and PAR1 modulate endothelial cell function in developing blood vessels and that thrombin's actions on endothelial cells-rather than on platelets, mesenchymal cells, or fibrinogen-contribute to vascular development and hemostasis in the mouse embryo.

A self-fertile species of Steinernema from Indonesia: further evidence of convergent evolution amongst entomopathogenic nematodes?

More than 20 species of the entomopathogenic nematode Steinernema have been described; to date, all reproduce exclusively by cross-fertilization of male and female individuals. Steinernema sp. strain T87 from Indonesia was found to consist largely of self-fertile hermaphrodites. Progeny were produced by morphological females both in insects (Galleria mellonella) and in hanging drops of insect haemolymph inoculated with a single infective juvenile. Sperm were present in the oviduct of unmated morphological females. Approximately 1% of infective juveniles developed into males, and males were also present in the second generation where they constituted 1-6% of the population. Under the same conditions the related species Steinernema longicaudum strain CB2B displayed typical steinernematid reproduction: cross-fertilization and a 1:1 sex ratio. It is argued that the development of hermaphroditism in Steinernema sp. T87 represents convergent evolution with Heterorhabditis, the other major genus of entomopathogenic nematode.

Occurrence and distribution of the entomopathogenic nematodes Steinernema spp. and Heterorhabditis indica in Indonesia

Soil samples from 79 sites on five islands of Indonesia were baited with insects for the recovery of entomopathogenic nematodes. Heterorhabditis and Steinernema were equally prevalent, and were recovered from 11.7% of samples representing 20.3% of sites sampled. Both genera were recovered from coastal sites only. Entomopathogenic nematodes were more prevalent on the Moluccan islands of Ambon and Seram than on Java or Bali. They were not detected on Sulawesi, where non-coastal sites only were sampled. RFLP analysis was used in the identification of nematode isolates. Heterorhabditis indica was the only heterorhabditid identified. Two RFLP types of Steinernema were identified.

Persistence of heterorhabditis infective juveniles in soil: comparison of extraction and infectivity measurements

The persistence of Heterorhabditis megidis in soil was studied over a 4-week period. On days 0, 2, 14, and 28, infective juveniles (IJ) were extracted by centrifugal flotation, Baermann funnel, and baiting of soil with Tenebrio molitor larvae, which were then dissected. Extraction efficiencies on day 0 were 82% by centrifugal flotation, 56% by Baermann funnel, and 19.8% by bait insect. The relative efficiency of the three methods changed over time. The relationship between the density of nematodes in the soil and the proportion recovered by dissection was non-linear. Up to a dose of approximately 60 IJ/insect, less than 12% became established, while at higher doses (up to 200 IJ/insect) the invasion efficiency was 23%. Mortality of bait insects increased from day 0 to day 2, but decreased to day 28. A novel method of assessing soil pathogenicity by preparing a soil density series and calculating the dose of soil or IJ that kills 50% of the bait insects gave a similar pattern. This method is recommended as a means of tracking changes in pathogenicity over time when bait insect mortality in undiluted soil is at or near 100%. Two methods of preparing a series of Heterorhabditis IJ densities in soil, either by diluting the soil itself with IJ-free soil or by adding diluted suspensions of IJ to the soil, resulted in the same bait insect mortalities.

Fatty acid composition of Heterorhabditis sp. during storage

The fatty acid composition of three North West European isolates of Heterorhabditis sp. from different geographical origins, UK211 (England), HF85 (The Netherlands) and EU17 (Estonia) was assessed directly after harvest and, for UK211 and HF85, after 5 weeks storage in water at 20 degrees C. Lipid represented 34-43% of the dry weight of fresh nematodes. Of this, neutral lipid (NL) comprised from 70% (HF85) to over 90% (UK211, EU17). The fatty acid patterns were similar between the three isolates. Oleic (C18:In-9), palmitic (C16:0), and linoleic (C18:2n-6) acid predominated with 51, 13 and 12%, respectively in the total lipid (TL) of fresh nematodes (average for the three isolates). Levels of unsaturation (U.I.) of fresh nematodes were on average 110, 112, 113 and 152 for the TL, NL, phospholipid and free fatty acid fractions, respectively. EU17 had a slightly lower U.I than the other two strains, despite its more northern origin. Changes in fatty acid composition due to storage were most significant in the NL fraction. The U.I. for the NL fraction increased during storage, suggesting a preferential use of saturated fatty acids.

Spontaneous follicular exclusion of SHP1-deficient B cells is conditional on the presence of competitor wild-type B cells

Engagement of antigen receptors on mature B lymphocytes is known to block cell entry into lymphoid follicles and promote accumulation in T cell zones, yet the molecular basis for this change in cell distribution is not understood. Previous studies have shown that follicular exclusion requires a threshold level of antigen receptor engagement combined with occupancy of follicles by B cells without equivalent receptor engagement. The possibility has been raised that follicular composition affects B cell positioning by altering the amount of available antigen and the degree of receptor occupancy. Here we show that follicular composition affects migration of mature B cells under conditions that are independent of antigen receptor occupancy. B cells deficient in the negative regulatory protein tyrosine phosphatase, SHP1, which have elevated intracellular signaling by the B cell receptor, are shown to accumulate in the T zone in the absence of their specific antigen. Follicular exclusion of SHP1-deficient B cells was found to be conditional on the presence of excess B cells that lack elevated intracellular signaling, and was not due to a failure of SHP-1-deficient cells to mature and express the follicle-homing chemokine receptor Burkitt's lymphoma receptor 1. These findings strongly suggest that signals that are negatively regulated by SHP1 promote B cell localization in T cell zones by reducing competitiveness for follicular entry, and provide further evidence that follicular composition influences the positioning of antigen-engaged B cells.

Estimation of lipid reserves in unstained living and dead nematodes by image analysis

During storage, non-feeding stages of entomopathogenic nematodes become visibly more transparent due to depletion of energy reserves. Optical density per unit area (OD per area) of infective juveniles of Steinernerna carpocapsae (All) and two Heterorhabditis isolates (UK211 and HF85) was measured with an image analysis system and compared with neutral lipid levels obtained by Oil Red O staining. Optical density (OD) measurements were compared with triglyceride levels of UK211 and HF85. Good correlations between OD per area and neutral lipids (0.90) and between OD and triglycerides (0.87) were found. Thus, OD reflects lipid levels and can be used as an indicator of lipid reserves in these nematodes. Heat-killing of nematodes had no significant effect on OD measurements, but length increased significantly. Storage in a triethanolamine in formaldehyde solution decreased the OD and OD/area by about 5% to 8%. An additional advantage of the image analysis method described is that repeated measurements can be performed on live nematodes. Key words: entomopathogenic nematode, Heterorhabditis, image analysis, neutral lipid, Oil Red O, optical density, Steinernema, triglyceride.