Negative regulation of PI 3-kinase by Ruk, a novel adaptor protein

Class I(A) phosphatidylinositol 3-kinase (PI 3-kinase) is a key component of important intracellular signalling cascades. We have identified an adaptor protein, Ruk(l), which forms complexes with the PI 3-kinase holoenzyme in vitro and in vivo. This interaction involves the proline-rich region of Ruk and the SH3 domain of the p85 alpha regulatory subunit of the class I(A) PI 3-kinase. In contrast to many other adaptor proteins that activate PI 3-kinase, interaction with Ruk(l) substantially inhibits the lipid kinase activity of the enzyme. Overexpression of Ruk(l) in cultured primary neurons induces apoptosis, an effect that could be reversed by co-expression of constitutively activated forms of the p110 alpha catalytic subunit of PI 3-kinase or its downstream effector PKB/Akt. Our data provide evidence for the existence of a negative regulator of the PI 3-kinase signalling pathway that is essential for maintaining cellular homeostasis. Structural similarities between Ruk, CIN85 and CD2AP/CMS suggest that these proteins form a novel family of adaptor molecules that are involved in various intracellular signalling pathways.

Induction of neuronal death by alpha-synuclein

The molecular and cellular mechanisms underlying neuronal loss in neurodegenerative diseases are unclear. It is generally thought that aggregation of mutated, abnormally modified or abnormally folded proteins leads to the accumulation of extracellular, intracellular or intranuclear deposits that severely compromise cell physiology, leading to the death of the affected neurons. However, there is growing evidence that neuronal apoptosis in the absence of obvious pathological deposits could have a serious impact on the pathogenesis of neurodegenerative diseases. alpha-Synuclein has been implicated in aetiology and pathogenesis of certain neurodegenerative diseases, although the precise role of this protein in neurodegeneration is uncertain. The normal functions of alpha-synuclein and other members of the synuclein family in the development and function of the nervous system also remain elusive. Here we show that overexpression of wild-type and mutant forms of alpha-synuclein in cultured neurons, but not the closely related persyn (gamma-synuclein), causes apoptosis. These findings suggest that abnormalities of alpha-synuclein metabolism could lead to the neuronal loss occurring in certain forms of neurodegeneration before the formation of characteristic pathological lesions.

MR imaging of lumbar facet joint synovial cysts

The increasing application of magnetic resonance (MR) imaging of the spine has raised the awareness of lumbar facet synovial cysts (LFSC). This well recognised, yet uncommon condition, presents with low back pain and radiculopathy due to the presence of an extradural mass. The commonest affected level is L4/5 with a mild degenerative spondylolisthesis a frequent associated finding. MR imaging is the technique of choice to detect and diagnose a LFSC. This pictorial essay, drawing on experience of 43 cases seen in 40 patients, illustrates the spectrum of appearances that can be encountered and suggest differing causes for the variable signal characteristics exhibited. Computed tomography (CT) can be of value in some cases to aid interpretation of the MR images. In addition, CT facet arthrography by injection of air or iodinated non-ionic contrast medium may be used to confirm the diagnosis in doubtful cases as well as noting whether the patients presenting symptoms can be provoked. A comprehensive review of the existing literature is presented.

Neurotrophins: more to NGF than just survival

NGF's role in neuronal survival has tended to mask other potential functions. But now the generation of mice lacking both Bax - required for the death of NGF-deprived neurons - and NGF or its receptor has shown that NGF plays a key role in establishing cutaneous innervation and regulating neuropeptide expression.

MR imaging of clear cell sarcoma (malignant melanoma of the soft parts): a multicenter correlative MRI-pathology study of 21 cases and literature review

OBJECTIVE

To evaluate MR imaging and pathology findings in order to define the characteristic features of clear cell sarcoma of the soft tissues (malignant melanoma of the soft parts).

DESIGN AND PATIENTS

MR examinations of 21 patients with histologically proven clear cell sarcoma of the musculoskeletal system were retrospectively reviewed and assessed for shape, homogeneity, delineation, signal intensities on T1- and T2-weighted images, contrast enhancement, relationship with adjacent fascia or tendon, secondary bone involvement, and intratumoral necrosis. In 19 cases the pathology findings were available for review and for a comparative MR-pathology study.

RESULTS

On T1-weighted images, lesions were isointense (n=3), hypointense (n=7) or slightly hyperintense to muscle (n=11). Immunohistochemical examination was performed in 17 patients. All 17 specimens showed positivity for HMB-45 antibody. In nine of 11 lesions with slightly increased signal intensity on T1-weighted images, a correlative MR imaging-pathology study was possible. All nine were positive to HMB-45 antibody.

CONCLUSIONS

Clear cell sarcoma of the musculoskeletal system often has a benign-looking appearance on MR images. In up to 52% of patients, this lesion with melanocytic differentiation has slightly increased signal intensity on T1-weighted images compared with muscle. As the presence of this relative higher signal intensity on T1-weighted images is rather specific for tumors displaying melanocytic differentiation, radiologists should familiarize themselves with this rare entity and include it in their differential diagnosis when confronted with a well-defined, homogeneous, strongly enhancing mass with slightly higher signal intensity compared with muscle on native T1-weighted images.

Depolarisation causes reciprocal changes in GFR(alpha)-1 and GFR(alpha)-2 receptor expression and shifts responsiveness to GDNF and neurturin in developing neurons

GDNF and neurturin are structurally related neurotrophic factors that promote the survival of many different kinds of neurons and influence axonal and dendritic growth and synaptic function. These diverse effects are mediated via multicomponent receptors consisting of the Ret receptor tyrosine kinase plus one of two structurally related GPI-linked receptors, GFR(alpha)-1 and GFR(alpha)-2. To ascertain how the expression of these receptors is regulated during development, we cultured embryonic neurons under different experimental conditions and used competitive RT/PCR to measure the levels of the mRNAs encoding these receptors. We found that depolarising levels of KCl caused a marked increase in GFR(alpha)-1 mRNA and a marked decrease in GFR(α)-2 mRNA in sympathetic, parasympathetic and sensory neurons. These changes were accompanied by increased responsiveness to GDNF and decreased responsiveness to neurturin, and were inhibited by L-type Ca(2+) channel antagonists, suggesting that they were due to elevated intracellular free-Ca(2+). There was no consistent effect of depolarising levels of KCl on ret mRNA expression, and neither GDNF nor neurturin significantly affected receptor expression. These results show that depolarisation has marked and opposing actions on the expression of GFR(α)-1 and GFR(α)-2, which are translated into corresponding changes in neuronal responsiveness to GDNF and neurturin. This provides evidence for a mechanism of regulating the neurotrophic factor responses of neurons by neural activity that has important implications for structural and functional plasticity in the developing nervous system.

Neurotrophins: neurotrophic modulation of neurite growth

As well as regulating neuronal survival, neurotrophins control the growth of axons and dendrites. New light has been shed on the mechanism of this latter control process by the discovery that the common neurotrophin receptor p75(NTR) interacts in a ligand-dependent manner with RhoA, a known regulator of actin assembly.

A randomized double-blind placebo-controlled crossover trial of the efficacy of L-arginine in the treatment of interstitial cystitis

OBJECTIVES

To determine, in a double-blind placebo-controlled crossover study, whether L-arginine improves the symptoms of interstitial cystitis (IC), a chronic condition in which nitric oxide (NO) may be important, as previous open pilot studies suggested that L-arginine reduced the pain and frequency associated with IC.

PATIENTS AND METHODS

Patients fulfilling the standard diagnostic criteria for IC were randomized to receive L-arginine (2.4 g/day) or placebo for one month. After a 2-week 'washout' period they received the other medication. Patients were assessed at each stage using a validated symptom index, a voiding diary, urine analysis and records of adverse events. Patients were asked about overall efficacy at the close of the study. The results were compared using a t-test, with significance indicated at P<0.05.

RESULTS

Sixteen (16) patients (mean age 51.3 years) were enrolled; the mean duration of IC was 5.4 years, the IC symptom index score 29.1, their nocturnal frequency 3.5 (voided volume 182 mL) and daytime frequency 12.7 (124 mL). Patients on placebo showed no differences in any recorded variable over the baseline values. L-arginine caused a statistically significant reduction in the overall symptom score of 2.2 over baseline, but there was no difference in voided volume, frequency or nocturia. As there was no significant difference for any variable between L-arginine and placebo, this reduction in score should be regarded with caution. Three patients withdrew because of side-effects (severe headaches, night sweats and flushing).

CONCLUSION

Oral L-arginine produces a statistically significant improvement in the IC symptom index in patients with IC, but the effect is small. This effect may not be clinically significant as there were no improvements in the other variables assessed and no significant difference between the response to L-arginine and placebo. From these results the use of L-arginine cannot be recommended for treating IC.

Differences in bcl-2- and bax-independent function in regulating apoptosis in sensory neuron populations

Bcl-2 and Bax are cytoplasmic proteins that have antagonistic actions on apoptosis. To investigate the extent to which these proteins function independently in regulating neuronal apoptosis, we studied the in vivo and in vitro development of two populations of sensory neurons of mouse embryos that lack one or both proteins. Absence of Bcl-2 increased neuronal apoptosis and reduced the number of neurons in both the trigeminal and nodose ganglia during the period of naturally occurring neuronal death. Absence of Bax reduced neuronal apoptosis and increased the number of surviving neurons in these ganglia and promoted sustained neuronal survival in neurotrophin-free cultures. In contrast, the elimination of both Bcl-2 and Bax had different consequences for these populations of neurons. In nodose ganglia, apoptosis was suppressed just as effectively in embryos lacking both proteins as in embryos lacking Bax alone, and neurons that lacked both proteins survived just as effectively in neurotrophin-free medium as Bax-deficient neurons. This suggests that for nodose neurons, the suppression of apoptosis by Bcl-2 is entirely dependent on the presence of Bax. In trigeminal ganglia, although neuronal apoptosis was reduced in embryos lacking both proteins compared with wild-type embryos, there were significantly more apoptotic neurons and significantly fewer surviving neurons in embryos lacking both proteins compared with Bax-deficient embryos, and significantly fewer trigeminal neurons from embryos lacking both proteins survived in neurotrophin-free medium compared with trigeminal neurons that lacked Bax alone. This suggests that for trigeminal neurons, Bcl-2 functions partly independently of Bax in regulating survival. Our results therefore suggest that the relative independence of Bcl-2 and Bax in regulating neuronal survival differs from one population of neurons to another.

In vivo survival requirement of a subset of nodose ganglion neurons for nerve growth factor

The sensory neurons of the nodose ganglion are the classic example of a population of peripheral nervous system neurons that do not require nerve growth factor (NGF) for survival during development but are dependent on other neurotrophins. We have re-examined this assertion by studying the development of the nodose ganglion of mice that have a null mutation in the NGF gene. Compared with wild-type embryos, the number of neurons undergoing apoptosis was elevated in NGF -/- mice, resulting in a significant reduction in the total number of neurons in the ganglion by the end of embryonic development. TrkA, the NGF receptor tyrosine kinase, was expressed in the nodose ganglion throughout development and there was a marked decrease in TrkA mRNA expression in the nodose ganglion of NGF -/- embryos. Although the in vitro survival of the majority of nodose neurons was promoted by brain-derived neurotrophic factor (BDNF), a minor proportion was supported by NGF in cultures established over a range of embryonic stages. These results clearly demonstrate that a subset of nodose ganglion neurons depends on NGF for survival during development. The finding that the expression of tyrosine hydroxylase (TH) mRNA was unaffected in the nodose ganglia of NGF-deficient embryos indicates that this NGF-dependent subset is distinct from the subset of catacholaminergic neurons in the nodose ganglion.

TrkB expression and early sensory neuron survival are independent of endogenous BDNF

Sensory neurons initially survive independently of neurotrophins in culture during the stage of development when their axons are growing to their targets. Because mRNAs encoding brain-derived neurotrophic factor (BDNF) and its receptor tyrosine kinase TrkB are detectable in subsets of sensory neurons from the earliest stages of their development, we investigated whether a BDNF autocrine loop is responsible for sustaining the survival of these neurons during this early stage in their development. Low-density dissociated cultures of nodose and dorsal root ganglion neurons were established from wild type and BDNF(-/-) mouse embryos at this stage and were grown in defined medium without added neurotrophins. Wild type and BDNF-deficient neurons survived equally well under these conditions, indicating that a BDNF autocrine loop does not play a role in sustaining the survival of sensory neurons during the earliest stages of their development. As sensory axons approach their targets, TrkB expression increases in a subset of neurons that becomes dependent on BDNF produced by other cells. Because numerous studies have shown that neurotrophins, including BDNF, increase expression of their receptors, we investigated whether endogenous BDNF is required for the increase in TrkB expression observed during stage of development. Quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) showed that the developmental increase in TrkB mRNA expression occurred normally in the sensory ganglia of BDNF(-/-) embryos. Taken together, our studies of sensory neuron development in BDNF-deficient embryos have demonstrated that endogenous BDNF is neither required for the early survival of these neurons nor for the induction of TrkB expression.

Cooperation between HGF and CNTF in promoting the survival and growth of sensory and parasympathetic neurons

Previous studies have shown that hepatocyte growth factor (HGF) enhances the survival and growth of neurons that depend on NGF for survival. To determine if HGF cooperates with other neurotrophic factors in the developing peripheral nervous system, we studied the effect of HGF on parasympathetic ciliary ganglion neurons and proprioceptive trigeminal mesencephalic nucleus (TMN) neurons, both of which survive with CNTF. HGF did not promote the survival of these neurons on its own but did enhance the number that survived with CNTF and increased the length and branching of their neurite arbors. HGF did not, however, enhance the survival and growth of TMN neurons incubated with BDNF, which promoted their survival as effectively as CNTF. These results show that HGF cooperates with CNTF in promoting the survival and growth of parasympathetic and proprioceptive neurons and that within the same neurons, the effects of HGF on survival and growth are selectively dependent on which other signaling pathways are concurrently activated.

Mutations in the gene encoding human persyn are not associated with amyotrophic lateral sclerosis or familial Parkinson's disease

The synucleins are a family of small proteins expressed in nervous tissue, which have been implicated in neurodegeneration. Using single strand conformation polymorphism analysis we screened for polymorphisms and mutations in the gene encoding human persyn, a recently discovered member of the synuclein family, in controls, patients with sporadic or familial amyotrophic lateral sclerosis (ALS) or familial Parkinson's disease (PD). Six polymorphisms in the genomic sequence of persyn were detected; A590C (5' untranslated region), G1943C (exon 3), G2049A (intron 3), T4502C (intron 3), T4552A (exon 4) and C5019T (3' untranslated region). However no associations with disease state were found in our sample group.

Developmental changes in the response of trigeminal neurons to neurotrophins: influence of birthdate and the ganglion environment

Previous studies have shown that most neurons in cultures established during the early stages of neurogenesis in the embryonic mouse trigeminal ganglion are supported by BDNF whereas most neurons cultured from older ganglia survive with NGF. To ascertain to what extent these developmental changes in neurotrophin responsiveness result from separate phases of generation of BDNF- and NGF-responsive neurons or from a developmental switch in the response of neurons from BDNF to NGF, we administered BrdU to pregnant mice at different stages of gestation to identify neurons born at different times and studied the survival of labelled neurons in dissociated cultures established shortly after BrdU administration. Most early-generated neurons responded to BDNF, neurons generated at intermediate times responded to both factors and late-generated neurons responded to NGF, indicating that there are overlapping phases in the generation of BDNF- and NGF-responsive neurons and that late-generated neurons do not switch responsiveness from BDNF to NGF. To ascertain if early-generated neurons do switch their response to neurotrophins during development, we used repeated BrdU injection to label all neurons generated after an early stage in neurogenesis and studied the neurotrophin responsiveness of the unlabelled neurons in cultures established after neurogenesis had ceased. The response of these early-generated neurons had decreased to BDNF and increased to NGF, indicating that at least a proportion of early-generated neurons switch responsiveness to neurotrophins in vivo. Because early-generated neurons do not switch responsiveness from BDNF to NGF in long-term dissociated cultures, we cultured early trigeminal ganglion explants with and without their targets for 24 hours before establishing dissociated cultures. This period of explant culture was sufficient to enable many early-generated neurons to switch their response from BDNF to NGF and this switch occurred irrespective of presence of target tissue. Our findings conclusively demonstrate for the first time that individual neurons switch their neurotrophin requirements during development and that this switch depends on cell interactions within the ganglion. In addition, we show that there are overlapping phases in the generation of BDNF- and NGF-responsive neurons in the trigeminal ganglion.

Selective regulation of trkC expression by NT3 in the developing peripheral nervous system

We have studied the influence of neurotrophin-3 (NT3) on the expression of its receptor tyrosine kinase, trkC, in embryonic mice. The expression of trkC transcripts encoding full-length and kinase-deficient receptors was almost entirely restricted to neurons in the trigeminal ganglion and increased markedly throughout development. In NT3(+/-) embryos, the level of trkC mRNA in the trigeminal ganglion was much lower than that in wild-type embryos, although there was no significant reduction in the total number of neurons in the ganglion. This demonstrates that endogenous NT3 regulates trkC expression in trigeminal neurons independently of changes in population size. In NT3(-/-) embryos, the number of neurons in the trigeminal ganglion was much lower than in wild-type embryos, and there was a further reduction in the mean neuronal level of trkC mRNA. Direct regulation of trkC mRNA expression in cultured trigeminal neurons was also observed, although the finding that trkC mRNA levels were sustained better in explant cultures than in dissociated cultures irrespective of the presence of NT3 suggests that trkC mRNA expression is regulated by additional factors within the ganglion. In contrast to trigeminal neurons, the level of trkC mRNA was sustained at normal levels in neurons of the sympathetic chain of NT3(-/-) embryos and was not increased by NT3 in sympathetic neuron cultures. TrkC mRNA expression in developing cutaneous tissues was also unaffected by the NT3 null mutation. In summary, our findings provide the first clear evidence that the expression of a trk receptor, tyrosine kinase, is regulated by physiological levels of its ligand in vivo and show that regulation by NT3 is cell type-specific.

A sequence-ready 840-kb PAC contig spanning the candidate tumor suppressor locus DBC1 on human chromosome 9q32-q33

A putative tumor suppressor locus involved in bladder cancer has been mapped to human chromosome 9q32-q33 and designated DBC1. Our previous microsatellite-based deletion mapping study indicated that DBC1 was localized between D9S1848 and AFMA239XA9. We have constructed an 840-kb sequence-ready contig composed of bacteriophage P1-derived artificial chromosomes (PACs), which encompasses DBC1. Clones were initially identified by screening a PAC library with markers localized to the region by physical mapping, and subsequently PAC end probes were used to complete the contig. This contig contains a minimum tiling path of six PAC clones between D9S1848 and AFMA239XA9. Three expressed sequence tags (ESTs) were mapped to the DBC1 region by screening 24 ESTs mapped to the surrounding area by radiation hybrids. One represented the gene for DBCCR1, a known candidate for DBC1, and the other two were novel. This contig and preliminary expression map form the basis for the identification of the bladder cancer tumor suppressor gene in this region.

p75-mediated NF-kappaB activation enhances the survival response of developing sensory neurons to nerve growth factor

We have investigated whether the transcription factor NF-kappaB plays a role in regulating neuronal survival by manipulating NF-kappaB activation in the nerve growth factor (NGF)-dependent sensory neurons of the embryonic mouse trigeminal ganglion. Overexpression of either the p65 or the p50 NF-kappaB subunits resulted in NF-kappaB activation and promoted in vitro survival as effectively as NGF. Expression of a superrepressor IkappaB-alpha protein prevented NF-kappaB activation in p65/p50-overexpressing neurons and caused the neurons to die as rapidly as NGF-deprived neurons. NGF treatment also activated NF-kappaB, and preventing this activation with superrepressor IkappaB-alpha reduced the NGF survival response. Antibodies that block binding of NGF to the p75 receptor prevented NGF-induced NF-kappaB activation and reduced the NGF survival response to the same extent as superrepressor IkappaB-alpha. Trigeminal neurons cultured from p65(-/-) embryos showed a reduced survival response to NGF compared with neurons from wild-type embryos and there was increased apoptosis of neurons in the trigeminal ganglia of p65(-/-) embryos in vivo. However, as with p75-deficient sensory neurons, p65-deficient sensory neurons showed a normal survival response to BDNF. These results reveal a role for NF-kappaB in regulating neuronal survival during embryonic development and suggest that in addition to the well-established Trk receptor tyrosine kinase signaling cascade, NGF enhances neuronal survival by signaling via a p75-mediated pathway.

Differences and developmental changes in the responsiveness of PNS neurons to GDNF and neurturin

We have studied the ability of GDNF and neurturin to promote the in vitro survival of populations of embryonic chicken parasympathetic, sympathetic, and sensory neurons. We show that these neurons are more responsive to one or other of these factors at particular stages of development. Whereas the parasympathetic neurons are more sensitive to neurturin at late embryonic stages, sympathetic neurons are more sensitive to neurturin at early stages. In contrast, sensory neurons of the nodose ganglion are more sensitive to GDNF throughout embryonic development. Using competitive RT/PCR, we measured the levels of mRNAs encoding GDNF and neurturin receptors in purified neurons. All neurons expressed Ret mRNA, which encodes the common receptor tyrosine kinase for GDNF and neurturin. Neurons that were more sensitive to GDNF expressed higher levels of GFRalpha-1 mRNA than GFRalpha-2 mRNA and neurons that were more sensitive to neurturin expressed higher levels of GFRalpha-2 mRNA than GFRalpha-1 mRNA. These results show that populations of PNS neurons differ markedly in their responsiveness to GDNF and neurturin at certain stages of the development and suggest that these differences are governed in part by the relative levels of expression of members of the GFRalpha family of GPI-linked receptors.

Urinary monitoring of saccharin and acesulfame-K as biomarkers of exposure to these additives

A method was developed to determine the levels of two intense sweeteners, saccharin and acesulfame-K, in human urine. Measurement of these two analytes in urine allowed an assessment to be made of dietary exposure to the sweeteners using intake/excretion curves. This paper describes an intake/excretion study in which 22 volunteers consumed known amounts of saccharin and acesulfame-K at five different levels ranging between 1.4 and 70 mg of saccharin (0.7-30% of the ADI for a 60 kg person) and 2.2-102 mg of acesulfame-K (0.4-19% of the ADI for a 60 kg person). Urine collections were then carried out by the volunteers for 24 h after each dose. The data obtained from this study were used to construct intake/excretion curves for both sweeteners. To test the methodology developed, 188 volunteers aged between 3 and 74 years were asked to carry out a 24-h urine collection whilst keeping a 48-h food diary. Comparison of the intake data obtained using the biomarker approach with the questionnaire-based results was generally good, although discrepancies due to the format and assessment of the questionnaire data were noticed.

Mutation of the 9q34 gene TSC1 in sporadic bladder cancer

Deletions involving chromosome 9 occur in more than 50% of human bladder cancers of all grades and stages. Most involve loss of the whole chromosome or of an entire chromosome arm but some small deletions are found which can be used to define critical regions which may contain tumour suppressor genes. We have localized such a critical region of deletion at 9q34 between the markers D9S149 and D9S66, an interval which contains the Tuberous Sclerosis gene TSC1. Single strand conformation polymorphism (SSCP) and sequence analysis of TSC1 in bladder tumours and cell lines with 9q34 loss of heterozygosity (LOH) has identified five mutations in retained TSC1 alleles. Our results support the hypothesis that TSC1 can act as a bladder tumour suppressor gene.

Follow-up of musculoskeletal tumours. 2. Metastatic disease

Both the prognosis and the morbidity of a patient with a primary malignant musculoskeletal tumour have improved over the past 25 years due to the advent of adjuvant chemotherapy and limb-sparing surgery. This has important implications for the role of imaging at the time of initial diagnosis and during follow-up. This pictorial essay reviews the imaging and pitfalls in the interpretation of musculoskeletal sarcoma metastases using a variety of radiological techniques. The optimal imaging strategy will be stressed.

SAPHO syndrome: 20-year follow-up

Considerable attention has been paid in the past 10 years to the radiological spectrum of disease entities belonging to the SAPHO syndrome. We report an unusual case presenting with an extra-axial (femoral) lesion, prior to description of this syndrome, which was radiologically and histologically mistaken for a parosteal osteosarcoma. Nineteen years later, a further lesion developed in the scapula together with the typical sternoclavicular manifestations, at which stage the correct diagnosis of SAPHO syndrome was established.

Osteochondroma and secondary synovial osteochondromatosis

Secondary synovial osteochondromatosis (SOC) is a rare disorder caused by a variety of joint disorders. Two unusual cases of secondary SOC are presented. The first patient is a 43-year-old man with extensive SOC developing within a bursa surrounding an osteochondroma of the pubic bone. The second patient is a 23-year-old man who developed florid and progressive SOC of his hip joint following excision of a femoral neck osteochondroma. SOC recurred despite three excisions over a 15-month period. Imaging was useful in pre-operative diagnosis of bursal SOC in the first patient and in detecting multiple recurrences in the second patient. Both cases illustrate prominent SOC developing secondary to osteochondroma. The different hypotheses regarding bursal and secondary SOC are reviewed.

Tumour volume as a predictor of necrosis after chemotherapy in Ewing's sarcoma

We studied the CT and MR scans, and the histology of 50 patients with primary Ewing's sarcoma of bone to determine the association between the change in tumour volume and necrosis after chemotherapy, and to ascertain their influence on prognosis. The mean age of the patients was 17 years. The limbs were involved in 40 and the axial bones in ten. The volume of the tumour at diagnosis varied from 31 to 1790 ml. There was a significant relationship between necrosis and the measured change in volume of the tumour after chemotherapy. Progression of the tumour despite chemotherapy was seen only in patients with necrosis of grades 4 to 6. Necrosis significantly influenced survival (p < 0.05), but the effect of change in volume was less significant. Change in volume of the tumour is a good predictor of necrosis induced by chemotherapy. Necrosis is a strong prognostic factor in Ewing's sarcoma.

Genomic structure and chromosomal localization of the mouse persyn gene

Synucleins are a family of small intracellular proteins expressed mainly in the nervous system. The involvement of synucleins in neurodegeneration and malignancy has been demonstrated, but the physiological functions of these proteins remain elusive. Further studies including generation of animals with modified persyn expression are necessary to clarify the functions of these proteins and the mechanisms of their involvement in human diseases. We cloned and determined the organization and chromosomal localization of the mouse gene coding for persyn, a member of the synuclein family. The gene is composed of five exons, and its general structure is very similar to that of the human persyn gene. Using fluorescence in situ hybridization, we assigned the persyn gene to the boundary of bands B and C on mouse chromosome 14. We found a fragment of the gene that directs expression of the persyn protein in sensory neurons and could be used for generation of transgenic animals.

Parosteal osteosarcoma of a metatarsal with intramedullary invasion

A 70-year-old man presented with increasing swelling of 2 years' duration, on the dorsal aspect of the forefoot. Imaging studies revealed a heavily calcified surface lesion of bone with early invasion of the underlying second metatarsal. Both imaging findings and the subsequent resection histology were consistent with a parosteal osteosarcoma, which is particularly rare at this site and at this age. The differential diagnosis of a mineralizing surface lesion of bone arising in the foot is discussed.

Regulation of neurotrophin receptor expression by retinoic acid in mouse sympathetic neuroblasts

We have studied the effect of retinoic acid on the expression of the neurotrophin receptors trkA, trkC, and p75 by neuroblasts and neurons at different axial levels along the embryonic mouse paravertebral sympathetic chain. In dissociated cultures of sympathetic neuroblasts, retinoic acid inhibited the developmental increase in trkA mRNA expression and the developmental decrease in trkC mRNA expression that normally occurs in these cells but did not affect p75 mRNA expression. At higher concentrations, retinoic acid also increased the proliferation of sympathetic neuroblasts. After sympathetic neuroblasts became postmitotic, retinoic acid no longer affected receptor expression. Studies with retinoic acid receptor agonists and antagonists indicated that the effects of retinoic acid on neurotrophin receptor expression were mediated mainly by alpha retinoic acid receptors, not beta or gamma receptors. The observation that alpha-antagonists increased trkA mRNA expression in intact sympathetic ganglion explants suggests that endogenous retinoic acid is a physiological regulator of trkA receptor expression.

Developmentally regulated expression of persyn, a member of the synuclein family, in skin

Synucleins constitute a group of unique, evolutionarily conserved proteins that are expressed predominantly in neurons of the central and peripheral nervous system. Although the normal cellular functions of synucleins are not clear, these proteins have been implicated in various neurodegenerative conditions in humans. We found that persyn, a recently characterized member of the synuclein family, is expressed not only in the nervous system but also in the stratum granulosum of the epidermis of neonatal and adult mice. This finding together with our recent observations that persyn influences neurofilament network integrity in sensory neurons raises the possibility that persyn in skin could be involved in modulation of the keratin network.

Double-stress fracture of the tibia in a ten-year-old child

A double-stress fracture of the tibia in a 10-year-old girl is described. Double-stress fracture of the tibia has previously been described in association with osteoarthritic varus deformity of the knee but not, to our knowledge, in a child. It is important to establish the diagnosis of stress fracture in childhood because the differential diagnosis, both clinically and on imaging, includes malignancy that must be excluded while avoiding unnecessary invasive investigations. The site of the lesions, their appearance on magnetic resonance imaging, the absence of any soft-tissue involvement, and the clinical history made the diagnosis possible. The characteristics of stress fracture shown on magnetic resonance imaging are described.

Persyn, a member of the synuclein family, has a distinct pattern of expression in the developing nervous system

The synucleins are a unique family of small intracellular proteins that have recently attracted considerable attention because of their involvement in human neurodegenerative diseases. We have cloned a new member of the synuclein family called persyn. In contrast to other synucleins, which are presynaptic proteins of CNS neurons, persyn is a cytosolic protein that is expressed predominantly in the cell bodies and axons of primary sensory neurons, sympathetic neurons, and motoneurons. Northern blotting, in situ hybridization, Western blotting, and immunohistochemistry revealed that persyn mRNA and protein are expressed in these neurons from the earliest stages of axonal outgrowth and are maintained at a high level throughout life. Persyn also becomes detectable in evolutionary recent regions of the brain by adulthood.

Sclerotome distribution of melorheostosis and multicentric fibromatosis

A case of melorheostosis affecting the C7 sclerotome is described, in association with synchronous multicentric fibromatosis. The foci of fibromatosis also affected the C7 sclerotome, suggesting a similar underlying pathogenesis for both diseases.

GFR alpha-4 and the tyrosine kinase Ret form a functional receptor complex for persephin

Glial-cell-line-derived neurotrophic factor (GDNF), neurturin and persephin are structurally related, secreted proteins that are widely expressed in the nervous system and other tissues and promote the survival of a variety of neurons during development. GDNF and neurturin signal through multicomponent receptors that consist of the Ret receptor tyrosine kinase and one of two structurally related glycosyl-phosphatidylinositol (GPI)-linked ligand-binding subunits: GFR alpha-1 is the preferred ligand-binding subunit for GDNF, and GFR alpha-2 is the preferred ligand-binding subunit for neurturin. Two additional members of the GFR alpha family of GPI-linked proteins have recently been cloned: GFR alpha-3 and GFR alpha-4. We have shown that persephin binds efficiently only to GFR alpha-4, and labelled persephin is effectively displaced from cells expressing GFR alpha-4 by persephin but not by GDNF or neurturin. Using microinjection to introduce expression plasmids into cultured neurons, we have also shown that coexpression of Ret with GFR alpha-4, confers a marked survival response to persephin but not to GDNF or neurturin. These results demonstrate that GFR alpha-4 is the ligand-binding subunit for persephin and that persephin, like GDNF and neurturin, also requires Ret for signalling.

Magnetic resonance imaging of soft tissue expanders used in the management of musculoskeletal sarcomas

A soft tissue expander is surgically inserted into the body to displace radiosensitive organs from the treatment field in a small number of patients receiving radiotherapy for musculoskeletal sarcoma. MRI is routinely used to monitor the response to the radiotherapy, local recurrence and complications of treatment. This study retrospectively reviews MRI of soft tissue expanders in seven patients with musculoskeletal sarcomas; six arising in the pelvis and one in the retroperitoneum. In the absence of an appropriate clinical history, the soft tissue expander may be mistaken for a pathological fluid collection such as abscess, post-operative seroma or even recurrent tumour. MRI of the soft tissue expanders and potential errors in image interpretation are illustrated.

Organization, expression and polymorphism of the human persyn gene

Persyn is a recently identified member of the synuclein family with a distinct pattern of expression during pre- and postnatal development of the mouse peripheral and central nervous systems. As with other synucleins, persyn is believed to be involved in the pathogenesis of human neurodegenerative diseases. However, in contrast to other synucleins, high levels of persyn mRNA expression were also found in advanced breast carcinomas, suggesting an involvement of the encoded protein in breast tumour progression. Here we have used an antibody specific to human persyn to demonstrate that the level of this protein is increased in ageing cerebral cortex and in breast tumours. We cloned, characterized and sequenced the human persyn genomic locus and localized it to the long arm of chromosome 10 in the q23.2-q23.3 region. Sequence information was used to search for specific mutations in the protein coding regions of persyn mRNA and the persyn gene in breast tumours and tumour cell lines. No tumour-specific mutations were found, but two linked polymorphisms in the coding region were detected, both in mRNA and exons III and IV of the gene. These results suggest that development of breast tumours correlates with overexpression of the wild-type persyn protein. Detailed characterization of the human persyn locus is important for further studies of the involvement of persyn in neurodegeneration and malignancy.

Point mutation in trkB causes loss of NT4-dependent neurons without major effects on diverse BDNF responses

Neurotrophins are a family of soluble ligands that promote the survival and differentiation of peripheral and central neurons and regulate synaptic function. The two neurotrophins, brain-derived neurotrophic factor (BDNF) and neurotrophin-4 (NT4), bind and activate a single high-affinity receptor, TrkB. Experiments in cell culture have revealed that an intact Shc adaptor binding site on TrkB and subsequent activation of the Ras/MAPK pathway are important for neuronal survival and neurite outgrowth. To elucidate the intracellular signaling pathways that mediate the diverse effects of BDNF and NT4 in vivo, we have mutated in the mouse germline the Shc binding site in the trkB gene. This trkB(shc) mutation revealed distinctive responses to BDNF and NT4. While nearly all NT4-dependent sensory neurons were lost in trkB(shc/shc) mutant mice, BDNF-dependent neurons were only modestly affected. Activation of MAP kinases and in vitro survival of cultured trkB(shc/shc) neurons were reduced in response to both neurotrophins, with NT4 being less potent than BDNF, suggesting differential activation of TrkB by the two ligands. Moreover, while the Ras/MAPK pathway is required for in vitro differentiation of neuronal cells, trkB(shc/shc) mutant mice do not show any defects in BDNF-dependent differentiation of CNS neurons or in the function of sensory neurons that mediate innocuous touch.

The 'penumbra sign' on T1-weighted MR imaging in subacute osteomyelitis: frequency, cause and significance

OBJECTIVE

We studied the frequency and cause of a feature exhibited on T1-weighted (T1-W) magnetic resonance (MR) imaging termed the 'penumbra sign' in a series of patients presenting with osteomyelitis and correlated it with the double-line sign described as a T2-weighted (T2-W) or short tau inversion recovery (STIR) feature of both the Brodie's abscess and avascular necrosis.

MATERIALS AND METHODS

The clinical, radiographic, MR imaging, microbiological and histological findings in 32 patients referred to an orthopaedic oncology service, but subsequently proven to have osteomyelitis, were reviewed. The presence or absence of a rim of tissue lining an abscess cavity typified by minor signal hyperintensity relative to the main abscess contents on T1-W MR imaging (the 'penumbra sign') was identified. The sign was correlated with the radiographic and other findings.

RESULTS

The penumbra sign was identified in 24 cases (75%) and appears to be a more sensitive sign than the corresponding double-line sign which was evident in only 29% of these on T2-W or fast STIR images. The lesions were unilocular in 11 cases (46%) and multilocular in 13 (54%). The thickness of the penumbra ranged from 2 to 5mm. On histological examination the tissue comprising the penumbra sign was found to be highly vascularized granulation tissue containing thick walled arterioles.

CONCLUSION

The penumbra sign is characteristically seen on T1-W MR images in subacute osteomyelitis and is due to a thick layer of highly vascularized granulation tissue which may not be visible as the double-line sign on T2-W or fast STIR sequences. This characteristic, but not pathognomonic, MR finding supports the diagnosis of bone infection and helps to exclude the presence of a tumour.

TrkB signalling inhibits p75-mediated apoptosis induced by nerve growth factor in embryonic proprioceptive neurons

Neurotrophins mediate their effects by binding to members of the Trk family of receptor tyrosine kinases and the neurotrophin receptor p75 [1]. Whereas Trks are essential for the trophic effects of neurotrophins [1], p75 has distinct functions in different cells. For example, it enhances the survival response of certain neurons to nerve growth factor (NGF) [2], but mediates a cytotoxic response to NGF in certain other cell types and neurons [3] [4] [5] [6]. We investigated whether the p75-mediated responses to NGF can be modulated through the activation of different signalling pathways in the same neurons. Neurons of the embryonic trigeminal mesencephalic nucleus (TMN) are supported in culture by brain-derived neurotrophic factor (BDNF) and an unrelated neurotrophic factor, ciliary neurotrophic factor (CNTF), but not by NGF [7] [8] [9]. We found that NGF killed TMN neurons that were grown in the presence of CNTF; this effect of NGF was inhibited by anti-p75 antibodies and therefore occurred via a p75-dependent mechanism. NGF did not affect the survival of neurons grown in the presence of BDNF, and very low concentrations of BDNF inhibited NGF cytotoxicity. These results indicate that the activation of different signalling pathways in TMN neurons influences their susceptibility to p75-mediated NGF cytotoxicity.

Follow-up of musculoskeletal tumors. I. Local recurrence

The prognosis for a patient with a musculoskeletal sarcoma has improved considerably over the past two decades largely due to the use of adjuvant chemotherapy. Surgical techniques have become more sophisticated with limb salvage, the preferred management in the majority of cases. Imaging plays an important role in the assessment of suspected local recurrence of tumor. This pictorial essay reviews the different imaging options and highlights various pitfalls in the detection and diagnosis of recurrence. The role of magnetic resonance imaging in this respect is stressed.

[Imaging of primary osteosarcoma]

Osteosarcoma is the most common primary malignant bone tumour with the exception of myeloma. The majority of osteosarcoma cases arise within bone and are called conventional osteosarcoma. Intraosseous variants include telangiectatic, small-cell, low-grade intraosseous and cortical osteosarcoma. Less than 10% of osteosarcomas arise on the surface of bone and are subdivided into periosteal, high-grade surface and parosteal varieties. The imaging features of these subtypes of osteosarcoma are described and the impact on diagnosis highlighted. Using material from over 750 osteosarcomas treated at the author's centre, this article reviews the role of imaging in the management of this condition. Detection still relies principally on the conventional radiograph with bone scintigraphy and MR imaging useful in occult tumours. Establishing the radiological diagnosis depends on careful analysis of the radiographs, with particular attention paid to the nature and extent of bone destruction, periosteal new bone formation and matrix mineralization. The prudent radiologist will be wary of those bone conditions, such as stress fractures and osteomyelitis, which are frequently mistaken for osteosarcoma. Appropriate surgical staging requires MR imaging of the primary tumour to show the bony and soft tissue extent of the lesion and to confirm/exclude skip metastases and local lymph-node involvement. Staging should also include bone scintigraphy to confirm/exclude multiple lesions and chest CT to confirm/exclude pulmonary metastases. Following definitive surgery, imaging is used in the follow-up to monitor potential local recurrence and the development of pulmonary or osseous metastases.

GFRalpha-4, a new GDNF family receptor

GFRalpha-1, GFRalpha-2, and GFRalpha-3 constitute a family of structurally related, glycosyl-phosphatidylinosital-linked, cell surface proteins, two of which, GFRalpha-1 and GFRalpha-2, are components of the receptor complex for the neurotrophic factors GDNF and neurturin, respectively. By screening an embryonic chicken brain cDNA library with a GFRalpha-1 probe at low stringency, we isolated cDNAs encoding an additional member of the GFRalpha family, GFRalpha-4. The nucleotide sequence predicts a 431-amino-acid secreted protein that is more closely related to GFRalpha-1 and GFRalpha-2 than to GFRalpha-3. GFRalpha-4 mRNA is expressed in distinctive patterns in the brain and several other organs and tissues of the chicken embryo. Our findings extend the family of GFRalpha proteins and provide information about the tissues in which GFRalpha-4 may function during development.

Bcl-2 accelerates the maturation of early sensory neurons

Bcl-2 is a cytoplasmic protein that blocks apoptosis in a wide variety of cell types. Here we report a novel role for Bcl-2 in the early stages of neuronal development. Shortly after differentiating from progenitor cells, sensory neurons undergo a distinct morphological change; initially they have small, spindle-shaped, phase-dark cell bodies that become large, spherical, and phase-bright. Early sensory neurons cultured from the trigeminal ganglia of bcl-2-/- embryos at embryonic day 11 (E11) and E12 underwent this change more slowly than trigeminal neurons of wild-type embryos of the same ages. The delay was not attributable to the well documented role of Bcl-2 in preventing apoptosis, because Bcl-2-deficient early sensory neurons survived as well as wild-type neurons. Accordingly, there was a significantly smaller number of the more mature type of neuron in the early trigeminal ganglia of bcl-2-/- embryos, yet the number of neurons in the trigeminal ganglia of bcl-2-/- and wild-type embryos was similar. The absence of Bcl-2 did not cause a uniform delay in the developmental program of sensory neurons, because the time course of nerve growth factor receptor expression (both trkA and p75) was unaffected in the trigeminal neurons of bcl-2-/- embryos. These findings indicate that Bcl-2 expression is required for the normal progression of a particular early maturational change in embryonic sensory neurons.

Multiple roles for hepatocyte growth factor in sympathetic neuron development

We have studied the role of hepatocyte growth factor (HGF)/Met signaling in the development of sympathetic neuroblasts and neurons. Anti-HGF antibodies reduced the number of sympathetic neuroblasts that differentiated into neurons, but neither anti-HGF antibodies nor HGF affected neuroblast proliferation. Anti-HGF antibodies also reduced the survival of neuroblasts but not sympathetic neurons. HGF greatly enhanced the neurite outgrowth of NGF-dependent sympathetic neurons throughout development. These in vitro effects of anti-HGF antibodies and HGF were abolished by a disabling mutation of Met, the HGF receptor tyrosine kinase. The Met mutation also increased sympathetic neuroblast apoptosis in vivo. Because Met and HGF are expressed in sympathetic ganglia throughout development, it is possible that the multiple effects of HGF/Met signaling on sympathetic neuroblasts and neurons occur in part by an autocrine mechanism.

NGF binding to p75 enhances the sensitivity of sensory and sympathetic neurons to NGF at different stages of development

To clarify the role of the common neurotrophin receptor p75 in modulating the survival response of sensory and sympathetic neurons to NGF at different stages of development, we compared the actions of wild-type NGF with a mutated NGF protein that binds normally to TrkA, the NGF receptor tyrosine kinase, but has greatly reduced binding to p75. At saturating concentrations, the NGF mutant promoted the survival of similar numbers of trigeminal sensory and sympathetic neurons as NGF. At subsaturating concentrations, the NGF mutant was less effective than wild-type NGF in promoting the survival of embryonic sensory neurons and postnatal sympathetic neurons but was equally effective as wild-type NGF in promoting the survival of embryonic sympathetic neurons. Whereas the levels of trkA and p75 were similar in embryonic sensory neurons and postnatal sympathetic neurons, the level of p75 was significantly lower than that of trkA in embryonic sympathetic neurons. These results indicate that binding of NGF to p75 enhances the sensitivity of NGF-dependent neurons to NGF at stages in their development when the levels of p75 and TrkA are similar.

Cytokines promote the survival of mouse cranial sensory neurones at different developmental stages

To investigate when the neurotrophic cytokines ciliary neurotrophic factor (CNTF), leukaemia inhibitory factor (LIF), oncostatin-M (OSM), interleukin-6 (IL-6) and cardiotrophin-1 (CT-1) act on developing sensory neurones and whether they co-operate with neurotrophins in regulating neuronal survival, we studied the in vitro trophic effects of these factors on two well-characterized populations of cranial sensory neurones at closely staged intervals throughout embryonic development. The cutaneous sensory neurones of the trigeminal ganglion, which show an early, transient survival response to BDNF and NT3 before becoming NGF-dependent, were supported by CNTF, LIF, OSM and CT-1 during the late fetal period, several days after the neurones become NGF-dependent. At this stage of development, these cytokines promoted the survival of a subset of NGF-responsive neurones. The enteroceptive neurones of the nodose ganglion, which retain dependence on BDNF throughout fetal development, were supported throughout their development by CNTF, LIF, OSM and CT-1, and displayed an additional survival response to IL-6 in the late fetal period. These findings indicate that populations of sensory neurones display different developmental patterns of cytokine responsiveness and show that embryonic trigeminal neurones pass through several phases of differing neurotrophic factor survival requirements.

Scintigraphically negative skip metastasis in osteosarcoma

The accurate pre-operative evaluation of the intramedullary extent of osteosarcoma is essential, as it determines the level of bone resection. Radiographs, isotope bone and MR imaging scans have been considered as reliable in detecting skeletal metastasis and skip lesions. We report a case of osteosarcoma of the distal femur with a large skip lesion proximally which was not visualized by either routine radiography or bone scintigraphy, and was not included within the scan field on the initial MR imaging scan. The implications on patient management and possible reasons for failure of imaging to reveal the skip metastasis are discussed.

Neuronal survival: early dependence on Schwann cells

Schwann cells fail to develop in mouse embryos lacking functional ErbB3 neuregulin receptors, and most sensory and motor neurons subsequently die in these mice. As ErbB3 acts cell autonomously in Schwann cell development but not in neuronal survival, neurons may depend on Schwann cells for survival.

Met receptor signaling is required for sensory nerve development and HGF promotes axonal growth and survival of sensory neurons

The development of the nervous system is a dynamic process during which factors act in an instructive fashion to direct the differentiation and survival of neurons, and to induce axonal outgrowth, guidance to, and terminal branching within the target tissue. Here we report that mice expressing signaling mutants of the hepatocyte growth factor (HGF) receptor, the Met tyrosine kinase, show a striking reduction of sensory nerves innervating the skin of the limbs and thorax, implicating the HGF/Met system in sensory neuron development. Using in vitro assays, we find that HGF cooperates with nerve growth factor (NGF) to enhance axonal outgrowth from cultured dorsal root ganglion (DRG) neurons. HGF also enhances the neurotrophic activities of NGF in vitro, and Met receptor signaling is required for the survival of a proportion of DRG neurons in vivo. This synergism is specific for NGF but not for the related neurotrophins BDNF and NT3. By using a mild signaling mutant of Met, we have demonstrated previously that Met requires signaling via the adapter molecule Grb2 to induce proliferation of myoblasts. In contrast, the actions of HGF on sensory neurons are mediated by Met effectors distinct from Grb2. Our findings demonstrate a requirement for Met signaling in neurons during development.

Ewing's sarcoma presenting as a solitary bone cyst

This report describes a rare case of Ewing's sarcoma presenting as a cystic lesion in the proximal humeral metaphysis. The clinical, pathological and radiological findings are described and discussed, with emphasis on the radiological appearances.