A five-gene molecular phylogeny reveals Parapanteles Ashmead (Hymenoptera: Braconidae) to be polyphyletic as currently composed.

Parapanteles Ashmead (Braconidae: Microgastrinae) is a medium-sized genus of microgastrine wasps that was erected over a century ago and lacks a unique synapomorphic character, and its monophyly has not been tested by any means. Parapanteles usually are parasitoids of large, unconcealed caterpillars (macrolepidoptera) and have been reared from an unusually large diversity of hosts for a relatively small microgastrine genus. We used Cytochrome Oxidase I sequences ("DNA barcodes") available for Parapanteles and other microgastrines to sample the generic diversity of described and undescribed species currently placed in Parapanteles, and then sequenced four additional genes for this subsample (wingless, elongation factor 1-alpha, ribosomal subunit 28s, and NADH dehydrogenase subunit 1). We constructed individual gene trees and concatenated Bayesian and maximum-likelihood phylogenies for this 5-gene subsample. In these phylogenies, most Parapanteles species formed a monophyletic clade within another genus, Dolichogenidea, while the remaining Parapanteles species were recovered polyphyletically within several other genera. The latter likely represent misidentified members of other morphologically similar genera. Species in the monophyletic clade containing most Parapanteles parasitized caterpillars from only five families - Erebidae (Arctiinae), Geometridae, Saturniidae, Notodontidae, and Crambidae. We do not make any formal taxonomic decisions here because we were not able to include representatives of type species for Parapanteles or other relevant genera, and because we feel such decisions should be reserved until a comprehensive morphological analysis of the boundaries of these genera is accomplished.

Omega-3 supplementation alters mitochondrial membrane composition and respiration kinetics in human skeletal muscle.

Studies have shown increased incorporation of omega-3 fatty acids into whole skeletal muscle following supplementation, although little has been done to investigate the potential impact on the fatty acid composition of mitochondrial membranes and the functional consequences on mitochondrial bioenergetics. Therefore, we supplemented young healthy male subjects (n = 18) with fish oils [2 g eicosapentaenoic acid (EPA) and 1 g docosahexanoic acid (DHA) per day] for 12 weeks and skeletal muscle biopsies were taken prior to (Pre) and following (Post) supplementation for the analysis of mitochondrial membrane phospholipid composition and various assessments of mitochondrial bioenergetics. Total EPA and DHA content in mitochondrial membranes increased (P < 0.05) ∼450 and ∼320%, respectively, and displaced some omega-6 species in several phospholipid populations. Mitochondrial respiration, determined in permeabilized muscle fibres, demonstrated no change in maximal substrate-supported respiration, or in the sensitivity (apparent Km) and maximal capacity for pyruvate-supported respiration. In contrast, mitochondrial responses during ADP titrations demonstrated an enhanced ADP sensitivity (decreased apparent Km) that was independent of the creatine kinase shuttle. As the content of ANT1, ANT2, and subunits of the electron transport chain were unaltered by supplementation, these data suggest that prolonged omega-3 intake improves ADP kinetics in human skeletal muscle mitochondria through alterations in membrane structure and/or post-translational modification of ATP synthase and ANT isoforms. Omega-3 supplementation also increased the capacity for mitochondrial reactive oxygen species emission without altering the content of oxidative products, suggesting the absence of oxidative damage. The current data strongly emphasize a role for omega-3s in reorganizing the composition of mitochondrial membranes while promoting improvements in ADP sensitivity.

Sequential Cdk1 and Plk1 phosphorylation of protein tyrosine phosphatase 1B promotes mitotic cell death.

Mitotic cell death following prolonged arrest is an important death mechanism that is not completely understood. This study shows that Protein Tyrosine Phosphatase 1B (PTP1B) undergoes phosphorylation during mitotic arrest induced by microtubule-targeting agents (MTAs) in chronic myeloid leukaemia cells. Inhibition of cyclin-dependent kinase 1 (Cdk1) or polo-like kinase 1 (Plk1) during mitosis prevents PTP1B phosphorylation, implicating these kinases in PTP1B phosphorylation. In support of this, Cdk1 and Plk1 co-immunoprecipitate with endogenous PTP1B from mitotic cells. In addition, active recombinant Cdk1-cyclin B1 directly phosphorylates PTP1B at serine 386 in a kinase assay. Recombinant Plk1 phosphorylates PTP1B on serine 286 and 393 in vitro, however, it requires a priming phosphorylation by Cdk1 at serine 386 highlighting a novel co-operation between Cdk1 and Plk1 in the regulation of PTP1B. Furthermore, overexpression of wild-type PTP1B induced mitotic cell death, which is potentiated by MTAs. Moreover, mutation of serine 286 abrogates the cell death induced by PTP1B, whereas mutation of serine 393 does not, highlighting the importance of serine 286 phosphorylation in the execution of mitotic cell death. Finally, phosphorylation on serine 286 enhanced PTP1B phosphatase activity. Collectively, these data reveal that PTP1B activity promotes mitotic cell death and is regulated by the co-operative action of Cdk1 and Plk1 during mitotic arrest.

The calcium-sensing receptor--a driver of colon cell differentiation.

Dietary Ca(2+) reduces colon cell proliferation and carcinogenesis, but it becomes ineffective or even tumor-promoting during carcinogenesis. It appears that Ca(2+) and the colon cell CaSR together brake the massive cell production in normal colon crypts. The rapid proliferation of the transit-amplifying (TA) progeny of the colon stem cells at the bases of the crypts is driven by the "Wnt" signaling mechanism that stimulates proliferogenic genes and prevents apoptogenesis. It appears that TA cell cycling stops and terminal differentiation starts when the cells reach a higher level in the crypt where there is enough external Ca(2+) to stimulate the expression of CaSRs, the signals from which stimulate the expression of E-cadherin. At this point the APC (adenomatous polyposis coli) protein appears and some of it enters the nucleus. There it removes the apoptogenesis shield and stops the beta-cateninTcf-4 complex from driving further TA cell proliferation by releasing beta-catenin from the nucleus, and delivering it to cytoplasmic APCaxinGSK-3beta complexes for ultimate proteasomal destruction. Cytoplasmic beta-catenin is prevented from returning to the nucleus by destruction in APCaxinGSK-3beta complexes or locked by the emerging E-cadherin into adherens junctions which link the cell to proliferatively shut-down functioning cells with APC-dependent cytoskeletons moving up and out of the crypt. A common first step in colon carcinogenesis is the loss of functional APC which results in the retention of proliferogenic nuclear beta-cateninTcf-4. This drives the eventual appearance of mutation accumulating, apoptosis-resistant clones the proliferation of which cannot be inhibited by external Ca(2+) because of CaSR-disabling gene mutations.

Effects of dopamine receptor D4 variation on alcohol and tobacco use and on novelty seeking: multivariate linkage and association analysis.

The dopamine D4 receptor gene contains a polymorphic sequence consisting of a variable number of 48-base-pair (bp) repeats, and there have been a number of reports that this polymorphism is associated with variation in novelty seeking or in substance abuse and addictive behaviors. In this study we have assessed the linkage and association of DRD4 genotype with novelty seeking, alcohol use, and smoking in a sample of 377 dizygotic twin pairs and 15 single twins recruited from the Australian Twin Registry (ATR). We found no evidence of linkage or association of the DRD4 locus with any of the phenotypes. We made use of repeated measures for some phenotypes to increase power by multivariate genetic analysis, but allelic effects were still non-significant. Specifically, it has been suggested that the DRD4 7-repeat allele is associated with increased novelty seeking in males but we found no evidence for this, despite considerable power to do so. We conclude that DRD4 variation does not have an effect on use of alcohol and the problems that arise from it, on smoking, or on novelty seeking behavior.

Variation in alcohol pharmacokinetics as a risk factor for alcohol dependence.

BACKGROUND: The significant association between alcohol dehydrogenase (ADH)-2 genotype and alcohol-dependence risk, demonstrated in both Asian and non-Asian populations, suggests a link between the metabolism of alcohol (ethanol) and individual differences in susceptibility to dependence. METHODS: We tested this hypothesis by following up on subjects who took part in the Alcohol Challenge Twin Study conducted in 1979-1981 and comparing the blood and breath alcohol results in that study between subjects who subsequently did or did not meet diagnostic criteria for lifetime alcohol dependence in 1992-1993. RESULTS: Subjects who met DSM-III-R criteria for lifetime alcohol dependence at follow-up had higher blood and breath alcohol values after alcohol challenge than never-dependent subjects. Multivariate analysis showed independent effects of susceptibility to alcohol dependence and smoking status on blood alcohol concentrations, whereas habitual alcohol intake at the time of the initial study had marginally significant effects. The risk of alcohol dependence was 2-fold higher in men and 3-fold higher in women with blood or breath alcohol concentrations in the highest quartile than in the lowest quartile. CONCLUSIONS: In view of this association and the known genetic influences on both alcohol pharmacokinetics and alcohol dependence, it is probable that part of the heritability of dependence is mediated by genes (other than the known ADH2 and ADH3 polymorphisms) affecting alcohol metabolism.

An integrative approach for studying the etiology of alcoholism and other addictions.

Studies of alcoholism etiology often focus on genetic or psychosocial approaches, but not both. Greater understanding of the etiology of alcohol, tobacco and other addictions will come from integration of these research traditions. A research approach is outlined to test three models for the etiology of addictions--behavioral undercontrol, pharmacologic vulnerability, negative affect regulation--addressing key questions including (i) mediators of genetic effects, (ii) genotype-environment correlation effects, (iii) genotype x environment interaction effects, (iv) the developmental unfolding of genetic and environmental effects, (v) subtyping including identification of distinct trajectories of substance involvement, (vi) identification of individual genes that contribute to risk, and (vii) the consequences of excessive use. By using coordinated research designs, including prospective assessment of adolescent twins and their siblings and parents; of adult substance dependent and control twins and their MZ and DZ cotwins, the spouses of these pairs, and their adolescent offspring; and of regular families; by selecting for gene-mapping approaches sibships screened for extreme concordance or discordance on quantitative indices of substance use; and by using experimental (drug challenge) as well as survey approaches, a number of key questions concerning addiction etiology can be addressed. We discuss complementary strengths and weaknesses of different sampling strategies, as well as methods to implement such an integrated approach illustrated for the study of alcoholism etiology. A coordinated program of twin and family studies will allow a comprehensive dissection of the interplay of genetic and environmental risk-factors in the etiology of alcoholism and other addictions.

Transforming growth factor beta (TGFbeta) mediates Schwann cell death in vitro and in vivo: examination of c-Jun activation, interactions with survival signals, and the relationship of TGFbeta-mediated death to Schwann cell differentiation.

In some situations, cell death in the nervous system is controlled by an interplay between survival factors and negative survival signals that actively induce apoptosis. The present work indicates that the survival of Schwann cells is regulated by such a dual mechanism involving the negative survival signal transforming growth factor beta (TGFbeta), a family of growth factors that is present in the Schwann cells themselves. We analyze the interactions between this putative autocrine death signal and previously defined paracrine and autocrine survival signals and show that expression of a dominant negative c-Jun inhibits TGFbeta-induced apoptosis. This and other findings pinpoint activation of c-Jun as a key downstream event in TGFbeta-induced Schwann cell death. The ability of TGFbeta to kill Schwann cells, like normal Schwann cell death in vivo, is under a strong developmental regulation, and we show that the decreasing ability of TGFbeta to kill older cells is attributable to a decreasing ability of TGFbeta to phosphorylate c-Jun in more differentiated cells.

Gamma glutamyl transferase.

Serum gamma-glutamyl transferase (GGT) has been widely used as an index of liver dysfunction and marker of alcohol intake. The last few years have seen improvements in these areas and advances in understanding of its physiological role in counteracting oxidative stress by breaking down extracellular glutathione and making its component amino acids available to the cells. Conditions that increase serum GGT, such as obstructive liver disease, high alcohol consumption, and use of enzyme-inducing drugs, lead to increased free radical production and the threat of glutathione depletion. However, the products of the GGT reaction may themselves lead to increased free radical production, particularly in the presence of iron. There have also been important advances in the definition of the associations between serum GGT and risk of coronary heart disease, Type 2 diabetes, and stroke. People with high serum GGT have higher mortality, partly because of the association between GGT and other risk factors and partly because GGT is an independent predictor of risk. This review aims to summarize the knowledge about GGT's clinical applications, to present information on its physiological roles, consider the results of epidemiological studies, and assess how far these separate areas can be combined into an integrated view.

Effects of alcohol consumption on indices of iron stores and of iron stores on alcohol intake markers.

BACKGROUND: Alcohol increases body iron stores. Alcohol and iron may increase oxidative stress and the risk of alcohol-related liver disease. The relationship between low or "safe" levels of alcohol use and indices of body iron stores, and the factors that affect the alcohol-iron relationship, have not been fully characterized. Other aspects of the biological response to alcohol use have been reported to depend on iron status. METHODS: We have measured serum iron, transferrin, and ferritin as indices of iron stores in 3375 adult twin subjects recruited through the Australian Twin Registry. Information on alcohol use and dependence and smoking was obtained from questionnaires and interviews. RESULTS: Serum iron and ferritin increased progressively across classes of alcohol intake. The effects of beer consumption were greater than those of wine or spirits. Ferritin concentration was significantly higher in subjects who had ever been alcohol dependent. There was no evidence of interactions between HFE genotype or body mass index and alcohol. Alcohol intake-adjusted carbohydrate-deficient transferrin was increased in women in the lowest quartile of ferritin results, whereas adjusted gamma-glutamyltransferase, aspartate aminotransferase, and alanine aminotransferase values were increased in subjects with high ferritin. CONCLUSIONS: Alcohol intake at low level increases ferritin and, by inference, body iron stores. This may be either beneficial or harmful, depending on circumstances. The response of biological markers of alcohol intake can be affected by body iron stores; this has implications for test sensitivity and specificity and for variation in biological responses to alcohol use.

Parathyroid hormone: an anabolic treatment for osteoporosis.

Osteoporosis is a disease characterised by low bone mass, structural deterioration of bone and increased risk of fracture. The prevalence, and cost, of osteoporosis is increasing dramatically with our ageing population and the World Health Organization now considers it to be the second-leading healthcare problem. All currently approved therapies for osteoporosis (eg., estrogen, bisphosphonates, calcitonin and selective estrogen receptor modulators) are anti-resorptive agents that act on osteoclasts to prevent further bone loss. A new class of bone anabolic agent capable of building mechanically strong new bone in patients with established osteoporosis is in development. While the parathyroid hormone (PTH) is classically considered to be a bone catabolic agent, when delivered intermittently at low doses PTH potently stimulates cortical and trabecular bone growth in animals humans. The native hPTH-(1-84) and its osteogenic fragment, hPTH-(1-34), have already entered Phase III clinical trials. Understanding the mechanism of PTH's osteogenic actions has led to the development of smaller PTH analogues which can also build mechanically normal bone in osteopenic rats. These new PTH analogues are promising candidates for treating osteoporosis in humans as they are as efficacious as hPTH-(1-84) and hPTH-(1-34), but there is evidence that they may have considerably less ability to induce hypercalcemia, the major side effect of PTH therapy. In addition to treating osteoporosis, PTHs may be used to promote fracture healing, to restore bone loss in immobilized patients, or following excessive glucocorticoid or prolonged spaceflight, and to treat psoriasis.

The effect of monocyclic and bicyclic analogs of human parathyroid hormone (hPTH)-(1-31)NH2 on bone formation and mechanical strength in ovariectomized rats.

The [Leu27]cyclo(Glu22-Lys26)-hPTH-(1-31)NH2 lactam is a stronger stimulator of adenylyl cyclase activity and a better stimulator of trabecular bone in the ovariectomized (OVX) rat model of osteopenia than hPTH-(1-31)NH2. This enhanced activity is due in large part to the stabilization of the amphiphilic receptor-binding alpha-helix in the Ser17-Gln29 region. The goal of the present study was to determine whether further cyclization could produce a more active hPTH analog. To this end, we compared the relative bioactivities of the bicyclic hPTH analog [Glu17,Leu27]cyclo(Lys13-Glu17,Glu22-Lys26)-hPTH-(1-31)NH2, made by replacing Ser17 with Glu17 and introducing a second lactam linkage between Lys13 and Glu17. The relative EC50 for adenylyl cyclase stimulation by the bicyclic hPTH analog was similar to the EC50 of the monocyclic [Leu27]cyclo(Glu22-Lys26)-hPTH-(1-31)NH2, but the bicyclic analog was still more active than hPTH-(1-31)NH2. As expected from adenylyl cyclase stimulation being responsible for PTH's anabolic action, the bicyclic hPTH analog [Glu17, Leu27]cyclo(Lys13-Glu17, Glu22-Lys26)-hPTH-(1-31)NH2 was able to increase femoral trabecular volume and thickness and mechanical strength in OVX rats, but it was no more effective than [Leu27]cyclo(Glu22-Lys26)-hPTH-(1-31)NH2 when injected once daily in a dose of 0.8 nmol/100 g body weight. Thus, further constraint of the conformation of hPTH-(1-31)NH2 by introducing two lactam link-ages between Lys13-Glu17 and Glu22-Lys26 did not raise the osteogenicity above that of the monocyclic analog.

Dominant-negative c-Jun promotes neuronal survival by reducing BIM expression and inhibiting mitochondrial cytochrome c release.

Sympathetic neurons require nerve growth factor for survival and die by apoptosis in its absence. Key steps in the death pathway include c-Jun activation, mitochondrial cytochrome c release, and caspase activation. Here, we show that neurons rescued from NGF withdrawal-induced apoptosis by expression of dominant-negative c-Jun do not release cytochrome c from their mitochondria. Furthermore, we find that the mRNA for BIM(EL), a proapoptotic BCL-2 family member, increases in level after NGF withdrawal and that this is reduced by dominant-negative c-Jun. Finally, overexpression of BIM(EL) in neurons induces cytochrome c redistribution and apoptosis in the presence of NGF, and neurons injected with Bim antisense oligonucleotides or isolated from Bim(-/-) knockout mice die more slowly after NGF withdrawal.

Stimulation of protein kinase C activity in cells expressing human parathyroid hormone receptors by C- and N-terminally truncated fragments of parathyroid hormone 1-34.

The parathyroid hormone (PTH) fragment PTH(1-34) stimulates adenylyl cyclase, phospholipase C (PLC), and protein kinase C's (PKCs) in cells that express human, opossum, or rodent type 1 PTH/PTH-related protein (PTHrP) receptors (PTHR1s). Certain carboxyl (C)-terminally truncated fragments of PTH(1-34), such as human PTH(1-31) [hPTH-(1-31)NH2], stimulate adenylyl cyclase but not PKCs in rat osteoblasts or PLC and PKCs in mouse kidney cells. The hPTH(1-31)NH2 peptide does fully stimulate PLC in HKRK B7 porcine renal epithelial cells that express 950,000 transfected hPTHR1s per cell. Amino (N)-terminally truncated fragments, such as bovine PTH(3-34) [bPTH(3-34)], hPTH(3-34)NH2, and hPTH(13-34), stimulate PKCs in Chinese hamster ovary (CHO) cells expressing transfected rat receptors, opossum kidney cells, and rat osteoblasts, but an intact N terminus is needed to stimulate PLC via human PTHR1s in HKRK B7 cells. We now report that the N-terminally truncated analogs bPTH(3-34)NH2 and hPTH(13-34)OH do activate PKC via human PTHR1s in HKRK B7 cells, although less effectively than hPTH(1-34)NH2 and hPTH(1-31)NH2. Moreover, in a homologous human cell system (normal foreskin fibroblasts), these N-terminally truncated fragments stimulate PKC activity as strongly as hPTH(1-34)NH2 and hPTH(1-31)NH2. Thus, it appears that unlike their opossum and rodent equivalents, hPTHR1s can stimulate both PLC and PKCs when activated by C-terminally truncated fragments of PTH(1-34). Furthermore, hPTHR1s, like the PTHR1s in rat osteoblasts, opossum kidney cells, and rat PTHR1-transfected CHO cells also can stimulate PKC activity by a mechanism that is independent of PLC. The efficiency with which the N-terminally truncated PTH peptides stimulate PKC activity depends on the cellular context in which the PTHR1s are expressed.

Direct inhibition of c-Jun N-terminal kinase in sympathetic neurones prevents c-jun promoter activation and NGF withdrawal-induced death.

c-Jun N-terminal kinases (JNKs) regulate gene expression by phosphorylating transcription factors, such as c-Jun. Studies with JNK: knockout mice suggest that JNK activity may be required for excitotoxin-induced apoptosis in the adult hippocampus and for apoptosis in the developing embryonic neural tube. Here we investigate the role of JNKs in classical neurotrophin-regulated developmental neuronal death by using nerve growth factor (NGF)-dependent sympathetic neurones. In this system, NGF withdrawal leads to an increase in JNK activity, an increase in c-Jun protein levels and c-Jun N-terminal phosphorylation before the cell death commitment point, and c-Jun activity is required for cell death. To inhibit JNK activity in sympathetic neurones we have used two different JNK inhibitors that act by distinct mechanisms: the compound SB 203580 and the JNK binding domain (JBD) of JNK interacting protein 1 (JIP-1). We demonstrate that JNK activity is required for c-Jun phosphorylation, c-jun promoter activation and NGF withdrawal-induced apoptosis. We also show that ATF-2, a c-Jun dimerization partner that can regulate c-jun gene expression, is activated following NGF deprivation. Finally, by co-expressing the JBD and a regulatable c-Jun dominant negative mutant we demonstrate that JNK and AP-1 function in the same pro-apoptotic signalling pathway after NGF withdrawal.

Genetic covariation of neuroticism with monoamine oxidase activity and smoking.

Variation in the personality trait of neuroticism is known to be affected by genetic influences, but despite a number of association studies, the genes involved have not yet been characterized. In a recent study of platelet monoamine oxidase in 1,551 twin subjects, we found a significant association between monoamine oxidase activity and scores on the Eysenck Personality Questionnaire neuroticism scale. Further analyses presented here indicate that both neuroticism and monoamine oxidase activity are associated with variation in smoking habits, and that adjusting for the effect of smoking strengthens the association between MAO and neuroticism. Analysis of the genetic and environmental sources of covariation between neuroticism, smoking, and monoamine oxidase activity show that approximately 8% of the genetic variance in neuroticism is due to the same additive genetic effects that contribute to variation in monoamine oxidase activity, suggesting that variation in neuroticism is associated in part with aspects of serotonin metabolism.

The parathyroid hormones: bone-forming agents for treatment of osteoporosis.

This is a 3-part article. Part 1 is an overview of bone formation and resorption and the consequences of estrogen loss on bone. Part 2 comprehensively reviews the most current data on the ability of a family of potent osteoblast-stimulating bone-builders, the native 84-amino-acid parathyroid hormone (PTH), and certain of its 31- to 38- amino-acid fragments to stimulate the growth of animal and human bones. These PTHs are currently in, or about to enter, clinical trial as treatment for postmenopausal osteoporosis. Part 3 provides a detailed consideration of how these PTHs might stimulate bone growth via PTH receptor signaling.

Structure and activities of constrained analogues of human parathyroid hormone and parathyroid hormone-related peptide: implications for receptor-activating conformations of the hormones.

Parathyroid hormone (PTH) has a helix-bend-helix structure in solution. Part of the C-terminal helix, residues 21-31, is amphiphilic and forms a critical receptor-binding region. Stabilization of this alpha-helix by lactam formation between residues spaced i, i + 4 on the polar face was previously reported to increase adenylyl cyclase-stimulating (AC) activity if between residues 22 and 26 but to diminish it if between residues 26 and 30 [Barbier et al. (1997) J. Med. Chem. 40, 1373-1380]. This work reports the effects of other cyclizations on the polar face, differing in ring size or position, on alpha-helix conformation, as measured by circular dichroism, and on AC-stimulating activity. All analogues cyclized between residues 22 and 26 had at least a 1. 5-fold increase in activity, suggesting an alpha-helical structure between about residues 21 and 26. Cyclization between residues 25 and 29 or residues 26 and 30 diminished activity by 20-30%, despite stabilizing alpha-helix, suggesting that residues 25-31 bind to the receptor in a helical, but not classical alpha-helical, conformation. Analogues cyclized between residues 13 and 17 had slightly increased activity. A bicyclic analogue, with lactams between residues 13 and 17 and residues 22 and 26, had about the same activity as that cyclized only between 22 and 26. Parathyroid hormone-related peptide (PTHrP) may bind in a manner similar to the common receptor, but hydrophobic moment calculations suggest that it must bind as a tighter helix in order to optimally present its hydrophobic residues to the receptor. Both PTHrP analogues cyclized between either residues 22 and 26 or residues 26 and 30 had more stable alpha-helices but reduced AC activities, consistent with this hypothesis.

c-Jun and the transcriptional control of neuronal apoptosis.

There has been considerable interest in the molecular mechanisms of apoptosis in mammalian neurons because this form of neuronal cell death is important for the normal development of the nervous system and because inappropriate neuronal apoptosis may contribute to the pathology of human neurodegenerative diseases. The aim of recent research has been to identify the key components of the cell death machinery in neurons and understand how the cell death programme is regulated by intracellular signalling pathways activated by the binding of neurotrophins or death factors to specific cell surface receptors. The aim of this commentary was to review research that has investigated the role of the Jun N-terminal kinase (JNK)/c-Jun signalling pathway in neuronal apoptosis, focusing in particular on work carried out with developing sympathetic neurons. Experiments with sympathetic neurons cultured in vitro, as well as with cerebellar granule neurons and differentiated PC12 cells, have demonstrated that JNK/c-Jun signalling can promote apoptosis following survival factor withdrawal. In addition, experiments with Jnk(-/-) knockout mice have provided evidence that Jnk3 may be required for apoptosis in the hippocampus in vivo following injection of kainic acid, an excitotoxin, and that Jnk1 and Jnk2 are required for apoptosis in the developing embryonic neural tube. However, in the embryonic forebrain, Jnk1 and Jnk2 have the opposite function and are necessary for the survival of developing cortical neurons. These results suggest that JNKs and c-Jun are important regulators of the cell death programme in the mammalian nervous system, but that their biological effects depend on the neuronal type and stage of development.