Regulation of Protein Interactions by Mps One Binder (MOB1) Phosphorylation

MOB1 is a multifunctional protein best characterized for its integrative role in regulating Hippo and NDR pathway signaling in metazoans and the Mitotic Exit Network in yeast. Human MOB1 binds both the upstream kinases MST1 and MST2 and the downstream AGC group kinases LATS1, LATS2, NDR1, and NDR2. Binding of MOB1 to MST1 and MST2 is mediated by its phosphopeptide-binding infrastructure, the specificity of which matches the phosphorylation consensus of MST1 and MST2. On the other hand, binding of MOB1 to the LATS and NDR kinases is mediated by a distinct interaction surface on MOB1. By assembling both upstream and downstream kinases into a single complex, MOB1 facilitates the activation of the latter by the former through a trans-phosphorylation event. Binding of MOB1 to its upstream partners also renders MOB1 a substrate, which serves to differentially regulate its two protein interaction activities (at least in vitro). Our previous interaction proteomics analysis revealed that beyond associating with MST1 (and MST2), MOB1A and MOB1B can associate in a phosphorylation-dependent manner with at least two other signaling complexes, one containing the Rho guanine exchange factors (DOCK6-8) and the other containing the serine/threonine phosphatase PP6. Whether these complexes are recruited through the same mode of interaction as MST1 and MST2 remains unknown. Here, through a comprehensive set of biochemical, biophysical, mutational and structural studies, we quantitatively assess how phosphorylation of MOB1A regulates its interaction with both MST kinases and LATS/NDR family kinases in vitro Using interaction proteomics, we validate the significance of our in vitro studies and also discover that the phosphorylation-dependent recruitment of PP6 phosphatase and Rho guanine exchange factor protein complexes differ in key respects from that elucidated for MST1 and MST2. Together our studies confirm and extend previous work to delineate the intricate regulatory steps in key signaling pathways.

Endosomal sorting of VAMP3 is regulated by PI4K2A

Specificity of membrane fusion in vesicular trafficking is dependent on proper subcellular distribution of soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs). Although SNARE complexes are fairly promiscuous in vitro, substantial specificity is achieved in cells owing to the spatial segregation and shielding of SNARE motifs prior to association with cognate Q-SNAREs. In this study, we identified phosphatidylinositol 4-kinase IIα (PI4K2A) as a binding partner of vesicle-associated membrane protein 3 (VAMP3), a small R-SNARE involved in recycling and retrograde transport, and found that the two proteins co-reside on tubulo-vesicular endosomes. PI4K2A knockdown inhibited VAMP3 trafficking to perinuclear membranes and impaired the rate of VAMP3-mediated recycling of the transferrin receptor. Moreover, depletion of PI4K2A significantly decreased association of VAMP3 with its cognate Q-SNARE Vti1a. Although binding of VAMP3 to PI4K2A did not require kinase activity, acute depletion of phosphatidylinositol 4-phosphate (PtdIns4P) on endosomes significantly delayed VAMP3 trafficking. Modulation of SNARE function by phospholipids had previously been proposed based on in vitro studies, and our study provides mechanistic evidence in support of these claims by identifying PI4K2A and PtdIns4P as regulators of an R-SNARE in intact cells.

Genome-wide identification of long noncoding natural antisense transcripts and their responses to light in Arabidopsis

Recent research on long noncoding RNAs (lncRNAs) has expanded our understanding of gene transcription regulation and the generation of cellular complexity. Depending on their genomic origins, lncRNAs can be transcribed from intergenic or intragenic regions or from introns of protein-coding genes. We have recently reported more than 6000 intergenic lncRNAs in Arabidopsis. Here, we systematically identified long noncoding natural antisense transcripts (lncNATs), defined as lncRNAs transcribed from the opposite DNA strand of coding or noncoding genes. We found a total of 37,238 sense–antisense transcript pairs and 70% of annotated mRNAs to be associated with antisense transcripts in Arabidopsis. These lncNATs could be reproducibly detected by different technical platforms, including strand-specific tiling arrays, Agilent custom expression arrays, strand-specific RNA-seq, and qRT-PCR experiments. Moreover, we investigated the expression profiles of sense–antisense pairs in response to light and observed spatial and developmental-specific light effects on 626 concordant and 766 discordant NAT pairs. Genes for a large number of the light-responsive NAT pairs are associated with histone modification peaks, and histone acetylation is dynamically correlated with light-responsive expression changes of NATs.

Protein interaction network of the mammalian Hippo pathway reveals mechanisms of kinase-phosphatase interactions

The Hippo pathway regulates organ size and tissue homeostasis in response to multiple stimuli, including cell density and mechanotransduction. Pharmacological inhibition of phosphatases can also stimulate Hippo signaling in cell culture. We defined the Hippo protein-protein interaction network with and without inhibition of serine and threonine phosphatases by okadaic acid. We identified 749 protein interactions, including 599 previously unrecognized interactions, and demonstrated that several interactions with serine and threonine phosphatases were phosphorylation-dependent. Mutation of the T-loop of MST2 (mammalian STE20-like protein kinase 2), which prevented autophosphorylation, disrupted its association with STRIPAK (striatin-interacting phosphatase and kinase complex). Deletion of the amino-terminal forkhead-associated domain of SLMAP (sarcolemmal membrane-associated protein), a component of the STRIPAK complex, prevented its association with MST1 and MST2. Phosphatase inhibition produced temporally distinct changes in proteins that interacted with MOB1A and MOB1B (Mps one binder kinase activator-like 1A and 1B) and promoted interactions with upstream Hippo pathway proteins, such as MST1 and MST2, and with the trimeric protein phosphatase 6 complex (PP6). Mutation of three basic amino acids that are part of a phospho-serine- and phospho-threonine-binding domain in human MOB1B prevented its interaction with MST1 and PP6 in cells treated with okadaic acid. Collectively, our results indicated that changes in phosphorylation orchestrate interactions between kinases and phosphatases in Hippo signaling, providing a putative mechanism for pathway regulation.

STK25 protein mediates TrkA and CCM2 protein-dependent death in pediatric tumor cells of neural origin

The TrkA receptor tyrosine kinase induces death in medulloblastoma cells via an interaction with the cerebral cavernous malformation 2 (CCM2) protein. We used affinity proteomics to identify the germinal center kinase class III (GCKIII) kinases STK24 and STK25 as novel CCM2 interactors. Down-modulation of STK25, but not STK24, rescued medulloblastoma cells from NGF-induced TrkA-dependent cell death, suggesting that STK25 is part of the death-signaling pathway initiated by TrkA and CCM2. CCM2 can be phosphorylated by STK25, and the kinase activity of STK25 is required for death signaling. Finally, STK25 expression in tumors is correlated with positive prognosis in neuroblastoma patients. These findings delineate a death-signaling pathway downstream of neurotrophic receptor tyrosine kinases that may provide targets for therapeutic intervention in pediatric tumors of neural origin.

Mass spectrometry approaches to study mammalian kinase and phosphatase associated proteins

Reversible phosphorylation events regulate critical aspects of cellular biology by affecting protein conformation, cellular localization, enzymatic activity and associations with interaction partners. Kinases and phosphatases interact not only with their substrates but also with regulatory subunits and other proteins, including scaffolds. In recent years, affinity purification coupled to mass spectrometry (AP-MS) has proven to be a powerful tool to identify protein-protein interactions (PPIs) involving kinases and phosphatases. In this review we outline general considerations for successful AP-MS, and describe strategies that we have used to characterize the interactions of kinases and phosphatases in human cells.

Two phosphatidylinositol 4-kinases control lysosomal delivery of the Gaucher disease enzyme, β-glucocerebrosidase

Trafficking of glucocerebrosidase (GBA) enzyme from the endoplasmic reticulum to the lysosome requires lysosomal integral membrane protein type 2 (LIMP-2), which is a receptor for GBA. This study shows that phosphatidylinositol 4-kinase (PI4K) type IIIβ controls the exit of LIMP-2/GBA complex from the Golgi, while PI4KIIα is required for the post-Golgi trafficking of the complex via the late endosomes.

Gaucher disease is a lysosomal storage disorder caused by a defect in the degradation of glucosylceramide catalyzed by the lysosomal enzyme β-glucocerebrosidase (GBA). GBA reaches lysosomes via association with its receptor, lysosomal integral membrane protein type 2 (LIMP-2). We found that distinct phosphatidylinositol 4-kinases (PI4Ks) play important roles at multiple steps in the trafficking pathway of the LIMP-2/GBA complex. Acute depletion of phosphatidylinositol 4-phosphate in the Golgi caused accumulation of LIMP-2 in this compartment, and PI4KIIIβ was found to be responsible for controlling the exit of LIMP-2 from the Golgi. In contrast, depletion of PI4KIIα blocked trafficking at a post-Golgi compartment, leading to accumulation of LIMP-2 in enlarged endosomal vesicles. PI4KIIα depletion also caused secretion of missorted GBA into the medium, which was attenuated by limiting LIMP-2/GBA exit from the Golgi by PI4KIIIβ inhibitors. These studies identified PI4KIIIβ and PI4KIIα as important regulators of lysosomal delivery of GBA, revealing a new element of control to sphingolipid homeostasis by phosphoinositides.

Structure-function analysis of core STRIPAK Proteins: a signaling complex implicated in Golgi polarization

Cerebral cavernous malformations (CCMs) are alterations in brain capillary architecture that can result in neurological deficits, seizures, or stroke. We recently demonstrated that CCM3, a protein mutated in familial CCMs, resides predominantly within the STRIPAK complex (striatin interacting phosphatase and kinase). Along with CCM3, STRIPAK contains the Ser/Thr phosphatase PP2A. The PP2A holoenzyme consists of a core catalytic subunit along with variable scaffolding and regulatory subunits. Within STRIPAK, striatin family members act as PP2A regulatory subunits. STRIPAK also contains all three members of a subfamily of Sterile 20 kinases called the GCKIII proteins (MST4, STK24, and STK25). Here, we report that striatins and CCM3 bridge the phosphatase and kinase components of STRIPAK and map the interacting regions on each protein. We show that striatins and CCM3 regulate the Golgi localization of MST4 in an opposite manner. Consistent with a previously described function for MST4 and CCM3 in Golgi positioning, depletion of CCM3 or striatins affects Golgi polarization, also in an opposite manner. We propose that STRIPAK regulates the balance between MST4 localization at the Golgi and in the cytosol to control Golgi positioning.

CCM3/PDCD10 heterodimerizes with germinal center kinase III (GCKIII) proteins using a mechanism analogous to CCM3 homodimerization

CCM3 mutations give rise to cerebral cavernous malformations (CCMs) of the vasculature through a mechanism that remains unclear. Interaction of CCM3 with the germinal center kinase III (GCKIII) subfamily of Sterile 20 protein kinases, MST4, STK24, and STK25, has been implicated in cardiovascular development in the zebrafish, raising the possibility that dysregulated GCKIII function may contribute to the etiology of CCM disease. Here, we show that the amino-terminal region of CCM3 is necessary and sufficient to bind directly to the C-terminal tail region of GCKIII proteins. This same region of CCM3 was shown previously to mediate homodimerization through the formation of an interdigitated α-helical domain. Sequence conservation and binding studies suggest that CCM3 may preferentially heterodimerize with GCKIII proteins through a manner structurally analogous to that employed for CCM3 homodimerization.

Hippocampus, amygdala and global brain changes 10 years after childhood traumatic brain injury

Traumatic brain injury (TBI) in children results in damage to the developing brain, particularly in severely injured individuals. Little is known, however, of the long-term structural aspects of the brain following childhood TBI. This study investigated the integrity of the brain 10 years post-TBI using magnetic resonance imaging volumetrics in a sample of 49 participants with mild, moderate and severe TBI, evaluated against a normative sample of 20 individuals from a pediatric database with comparable age and gender distribution. Structural integrity was investigated in gray and white matter, and by manually segmenting two regions of interest (hippocampus, amygdala), potentially vulnerable to the effects of childhood TBI. The results indicate that more severe injuries caused a reduction in gray and white brain matter, while all TBI severity levels resulted in increased volumes of cerebrospinal fluid and smaller hippocampal volumes. In addition, enlarged amygdala volumes were detected in severely injured patients compared to their mild and moderate counterparts, suggesting that childhood TBI may disrupt the development of certain brain regions through diffuse pathological changes. The findings highlight the lasting impact of childhood TBI on the brain and the importance of monitoring brain structure in the long-term after early injury.

Lamellipodium extension and membrane ruffling require different SNARE-mediated trafficking pathways

Background

Intracellular membrane traffic is an essential component of the membrane remodeling that supports lamellipodium extension during cell adhesion. The membrane trafficking pathways that contribute to cell adhesion have not been fully elucidated, but recent studies have implicated SNARE proteins. Here, the functions of several SNAREs (SNAP23, VAMP3, VAMP4 and syntaxin13) are characterized during the processes of cell spreading and membrane ruffling.

Results

We report the first description of a SNARE complex, containing SNAP23, syntaxin13 and cellubrevin/VAMP3, that is induced by cell adhesion to an extracellular matrix. Impairing the function of the SNAREs in the complex using inhibitory SNARE domains disrupted the recycling endosome, impeded delivery of integrins to the cell surface, and reduced haptotactic cell migration and spreading. Blocking SNAP23 also inhibited the formation of PMA-stimulated, F-actin-rich membrane ruffles; however, membrane ruffle formation was not significantly altered by inhibition of VAMP3 or syntaxin13. In contrast, membrane ruffling, and not cell spreading, was sensitive to inhibition of two SNAREs within the biosynthetic secretory pathway, GS15 and VAMP4. Consistent with this, formation of a complex containing VAMP4 and SNAP23 was enhanced by treatment of cells with PMA. The results reveal a requirement for the function of a SNAP23-syntaxin13-VAMP3 complex in the formation of lamellipodia during cell adhesion and of a VAMP4-SNAP23-containing complex during PMA-induced membrane ruffling.

Conclusions

Our findings suggest that different SNARE-mediated trafficking pathways support membrane remodeling during ECM-induced lamellipodium extension and PMA-induced ruffle formation, pointing to important mechanistic differences between these processes.

VAMP3, syntaxin-13 and SNAP23 are involved in secretion of matrix metalloproteinases, degradation of the extracellular matrix and cell invasion

Cellular remodeling of the extracellular matrix (ECM), an essential component of many physiological and pathological processes, is dependent on the trafficking and secretion of matrix metalloproteinases (MMPs). Soluble NSF attachment protein receptor (SNARE)-mediated membrane traffic has documented roles in cell-ECM interactions and the present study specifically examines SNARE function in the trafficking of MMPs during ECM degradation. Using the invasive human fibrosarcoma cell line HT-1080, we demonstrate that a plasma membrane SNARE, SNAP23, and an endosomal v-SNARE, VAMP3 (also known as cellubrevin), partly colocalize with MMP2 and MMP9, and that inhibition of these SNAREs using dominant-negative SNARE mutants impaired secretion of the MMPs. Inhibition of VAMP3, SNAP23 or syntaxin-13 using dominant-negative SNARES, RNA interference or tetanus toxin impaired trafficking of membrane type 1 MMP to the cell surface. Consistent with these observations, we found that blocking the function of these SNAREs reduced the ability of HT-1080 cells to degrade a gelatin substrate in situ and impaired invasion of HT-1080 cells in vitro. The results reveal the importance of VAMP3, syntaxin-13 and SNAP23 in the trafficking of MMP during degradation of ECM substrates and subsequent cellular invasion.

A PP2A phosphatase high density interaction network identifies a novel striatin-interacting phosphatase and kinase complex linked to the cerebral cavernous malformation 3 (CCM3) protein

The serine/threonine protein phosphatases are targeted to specific subcellular locations and substrates in part via interactions with a wide variety of regulatory proteins. Understanding these interactions is thus critical to understanding phosphatase function. Using an iterative affinity purification/mass spectrometry approach, we generated a high density interaction map surrounding the protein phosphatase 2A catalytic subunit. This approach recapitulated the assembly of the PP2A catalytic subunit into many different trimeric complexes but also revealed several new protein-protein interactions. Here we define a novel large multiprotein assembly, referred to as the striatin-interacting phosphatase and kinase (STRIPAK) complex. STRIPAK contains the PP2A catalytic (PP2Ac) and scaffolding (PP2A A) subunits, the striatins (PP2A regulatory B''' subunits), the striatin-associated protein Mob3, the novel proteins STRIP1 and STRIP2 (formerly FAM40A and FAM40B), the cerebral cavernous malformation 3 (CCM3) protein, and members of the germinal center kinase III family of Ste20 kinases. Although the function of the CCM3 protein is unknown, the CCM3 gene is mutated in familial cerebral cavernous malformations, a condition associated with seizures and strokes. Our proteomics survey indicates that a large portion of the CCM3 protein resides within the STRIPAK complex, opening the way for further studies of CCM3 biology. The STRIPAK assembly establishes mutually exclusive interactions with either the CTTNBP2 proteins (which interact with the cytoskeletal protein cortactin) or a second subcomplex consisting of the sarcolemmal membrane-associated protein (SLMAP) and the related coiled-coil proteins suppressor of IKKepsilon (SIKE) and FGFR1OP2. We have thus identified several novel PP2A-containing protein complexes, including a large assembly linking kinases and phosphatases to a gene mutated in human disease.

Insights into the acute cerebral metabolic changes associated with childhood diabetes

AIMS

Type 1 diabetes is a prevalent chronic disease in childhood with the commonest single cause of death being cerebral oedema in the context of diabetic ketoacidosis (DKA). The nature of the alterations in cerebral metabolism that may result in vulnerability to neuronal injury remains unknown. The aim of this study was to analyse the magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) brain data from eight children with diabetes following acute presentation with hyperglycaemia with or without ketoacidosis, to determine the nature and timing of any alterations in cerebral structure and metabolism.

METHODS

This study used MRI and MRS to investigate regional cerebral abnormalities in a small series of diabetic patients with and without DKA. Changes were compared with the clinical and biochemical features of the patients studied.

RESULTS

Our small series of patients all demonstrated abnormal signal changes in the frontal region on fluid attenuated inversion recovery (FLAIR) MR imaging, suggestive of oedema, and spectroscopic abnormalities of increased taurine, myoinositol and glucose levels. The MR abnormalities varied in severity but did not correlate with any clinical or biochemical parameters.

CONCLUSIONS

These changes indicate that many diabetic children, particularly at presentation, may have alterations in cerebral metabolism with implications for the pathogenesis and treatment of the cerebral complications of DKA. In addition, our findings suggest that increased taurine may be one of the important differentiating factors in the response of the brain of diabetic children to DKA that may reflect an increase in their vulnerability to cerebral oedema compared with diabetic adults.

Inhibition of SNARE-mediated membrane traffic impairs cell migration

Cell migration occurs as a highly-regulated cycle of cell polarization, membrane extension at the leading edge, adhesion, contraction of the cell body, and release from the extracellular matrix at the trailing edge. In this study, we investigated the involvement of SNARE-mediated membrane trafficking in cell migration. Using a dominant-negative form of the enzyme N-ethylmaleimide-sensitive factor as a general inhibitor of SNARE-mediated membrane traffic and tetanus toxin as a specific inhibitor of VAMP3/cellubrevin, we conducted transwell migration assays and determined that serum-induced migration of CHO-K1 cells is dependant upon SNARE function. Both VAMP3-mediated and VAMP3-independent traffic were involved in regulating this cell migration. Inhibition of SNARE-mediated membrane traffic led to a decrease in the protrusion of lamellipodia at the leading edge of migrating cells. Additionally, the reduction in cell migration resulting from the inhibition of SNARE function was accompanied by perturbation of a Rab11-containing alpha(5)beta(1) integrin compartment and a decrease in cell surface alpha(5)beta(1) without alteration to total cellular integrin levels. Together, these observations suggest that inhibition of SNARE-mediated traffic interferes with the intracellular distribution of integrins and with the membrane remodeling that contributes to lamellipodial extension during cell migration.

Clinical and neuroradiologic features of acute disseminated encephalomyelitis in children

OBJECTIVE

To identify the clinical and neuroradiologic features of acute disseminated encephalomyelitis (ADEM) in childhood.

METHODS

A retrospective review was conducted of the medical records and MRI of children who presented to the Royal Children's Hospital in Melbourne with ADEM between January 1993 and December 1998.

RESULTS

Of the 31 patients included in this study, 22 (71%) experienced a prodromal illness. Two patients (6%) had received hepatitis B vaccine 3 to 6 weeks before developing their illness. Symptoms and signs typically evolved over several days. Ataxia was the most common presenting feature, occurring in 20 patients (65%). MRI findings were variable, but lesions were most commonly seen bilaterally and asymmetrically in the frontal and parietal lobes. The authors found a high incidence of the corpus callosal and periventricular changes more typically associated with MS, but they also found a high rate of deep gray matter involvement (61% of patients). The use of high-dose IV methylprednisolone was usually associated with rapid recovery. Eighty-one percent of patients recovered completely, with only mild sequelae recorded in the remaining children.

CONCLUSION

In the absence of a biological marker, the distinction between ADEM and MS cannot be made with certainty at the time of first presentation, but the authors suggest that a viral prodrome, early-onset ataxia, high lesion load on MRI, involvement of the deep gray matter, and absence of oligoclonal bands are more indicative of ADEM.

Clinical and imaging features of cortical malformations in childhood

OBJECTIVE

To determine the types, relative frequencies, clinical features, and MRI characteristics of malformations of cortical development (MCD) occurring in a cohort of children referred to a tertiary pediatric center.

METHODS

Original MR images were reviewed by two investigators, who were blinded to clinical details, to determine the elemental imaging features of each malformation and to label these malformations according to an existing system of classification. Clinical information was collected by a review of hospital records.

RESULTS

A total of 109 children with MCD were identified. There were 58 boys and 51 girls, age 8 days to 18 years at initial imaging (mean age, 5 years). Seizures were present in 75%, developmental delay or intellectual disability in 68%, abnormal neurologic findings in 48%, and congenital anomalies apart from the CNS malformation in 18%. The main malformations identified were heterotopic gray matter (19%), cortical tubers (17%), focal cortical dysplasia (16%), polymicrogyria (16%), agyria/pachygyria (15%), schizencephaly/cleft (5%), transmantle dysplasia (5%), and hemimegalencephaly (4%). Eight patients had features of more than one malformation. Most lesions were multilobar (47%), with the frontal lobe being the most common lobe involved (78%). A total of 68% of patients had other cerebral malformations including ventricular dilatation or dysmorphism (46%) and abnormalities of the corpus callosum (29%).

CONCLUSIONS

This study illustrates the spectrum of MCD in a pediatric cohort and highlights some of the differences between pediatric and adult patients. Patients with MCD presenting in childhood have a wider spectrum of malformations and more varied, often more severe, clinical manifestations. The lesions are frequently multifocal or generalized and many are associated with noncortical developmental brain anomalies.

Congenital muscular dystrophy, white-matter abnormalities, and neuronal migration disorders: the expanding concept

The congenital muscular dystrophies are a heterogeneous, recessively inherited group of disorders that have been subclassified on the basis of clinical central nervous system involvement. We report two children with "pure" congenital muscular dystrophy, one merosin negative and one merosin positive with extensive white matter and occipital cortical neuromigration abnormalities on magnetic resonance imaging (MRI). The first patient (merosin-negative congenital muscular dystrophy) presented with hypotonia and weakness in the neonatal period and subsequently was found to have a leukoencephalopathy and occipital cortical dysplasia on magnetic resonance imaging. The second patient presented with developmental delay without definite weakness. Initial investigations revealed a leukoencephalopathy and cortical dysplasia, but the patient subsequently was shown to have merosin-positive congenital muscular dystrophy. These patients illustrate that white-matter changes are not specific for merosin-negative congenital muscular dystrophy alone and that extensive cortical abnormality can be found in both groups of patients. In addition, our second patient illustrates a nonmuscular mode of congenital muscular dystrophy presentation that should be considered in patients with a "nonprogressive leukodystrophy."

Stroke and fibromuscular dysplasia: confirmation by renal magnetic resonance angiography

Childhood stroke is uncommon and may require extensive evaluation to elucidate an underlying cause. A 9-year-old boy had clinical and magnetic resonance imaging (MRI) features of an ischemic event in the left middle cerebral artery territory. Magnetic resonance angiography (MRA) revealed beading of the left middle cerebral artery, consistent with irregular blood flow secondary to turbulence or luminal narrowing. Conventional angiography of the cerebral vessels confirmed the findings of cerebral MRA and raised further the suspicion of fibromuscular dysplasia (FMD). MRA of the renal vessels was subsequently performed, revealing beading of the left renal artery and confirming the diagnosis of FMD. MRA, a rapid and less invasive technique associated with far less morbidity and mortality as compared with conventional angiography, may prove to be as sensitive as conventional angiography in detecting the changes of FMD. MRA of the renal arteries should be performed with initial cranial MRI and MRA in children who present with cerebral infarction of possible vascular origin. This may obviate the need to perform further investigations and may make early diagnosis possible at the first MRI scan and under a single general anesthetic.