Interval growth in an ICA bifurcation aneurysm treated with balloon occlusion, and possible contribution of vasa vasorum hypertrophy.

We present a rare case of an ICA aneurysm recurrence despite treatment with ICA balloon occlusion. There was evidence of ICA recanalization bypassing the balloons on a catheter angiogram follow-up 1 year post-procedure. Although initially stable in size, at 5 years after the original procedure, the aneurysm demonstrated evidence of enlargement and on angiography there was further enlargement of the recanalized ICA around the occluding balloons. We postulate that this has been caused by increasing antegrade flow through hypertrophied vasa vasorum in response to persistently increased demand for blood flow by the ipsilateral hemisphere; this indirectly may have also contributed to some extent to the aneurysm enlargement.

Ischaemic stroke in a 21-year-old with hereditary haemorrhagic telangiectasia.

A 21-year-old man presented with an acute ischaemic stroke. He had a history of epistaxis and a family history of hereditary haemorrhagic telangiectasia. We gave thrombolysis after some deliberation, and he made a good neurological recovery. This case highlights the link between hereditary haemorrhagic telangiectasia and ischaemic stroke, the potential risks of thrombolysis in such patients and the need to consider pulmonary arteriovenous malformations in patients with stroke.

Paediatric cerebrovascular CT angiography-towards better image quality.

BACKGROUND: Paediatric cerebrovascular CT angiography (CTA) can be challenging to perform due to variable cardiovascular physiology between different age groups and the risk of movement artefact. This analysis aimed to determine what proportion of CTA at our institution was of diagnostic quality and identify technical factors which could be improved. MATERIALS AND METHODS: a retrospective analysis of 20 cases was performed at a national paediatric neurovascular centre assessing image quality with a subjective scoring system and Hounsfield Unit (HU) measurements. Demographic data, contrast dose, flow rate and triggering times were recorded for each patient. RESULTS: Using a qualitative scoring system, 75% of studies were found to be of diagnostic quality (n=9 'good', n=6 'satisfactory') and 25% (n=5) were 'poor'. Those judged subjectively to be poor had arterial contrast density measured at less than 250 HU. Increased arterial opacification was achieved for cases performed with an increased flow rate (2.5-4 mL/s) and higher intravenous contrast dose (2 mL/kg). Triggering was found to be well timed in nine cases, early in four cases and late in seven cases. Of the scans triggered early, 75% were poor. Of the scans triggered late, less (29%) were poor. CONCLUSIONS: High flow rates (>2.5 mL/s) were a key factor for achieving high quality paediatric cerebrovascular CTA imaging. However, appropriate triggering by starting the scan immediately on contrast opacification of the monitoring vessel plays an important role and could maintain image quality when flow rates were lower. Early triggering appeared more detrimental than late.

Regulation of ribonucleotide reductase by Spd1 involves multiple mechanisms.

The correct levels of deoxyribonucleotide triphosphates and their relative abundance are important to maintain genomic integrity. Ribonucleotide reductase (RNR) regulation is complex and multifaceted. RNR is regulated allosterically by two nucleotide-binding sites, by transcriptional control, and by small inhibitory proteins that associate with the R1 catalytic subunit. In addition, the subcellular localization of the R2 subunit is regulated through the cell cycle and in response to DNA damage. We show that the fission yeast small RNR inhibitor Spd1 is intrinsically disordered and regulates R2 nuclear import, as predicted by its relationship to Saccharomyces cerevisiae Dif1. We demonstrate that Spd1 can interact with both R1 and R2, and show that the major restraint of RNR in vivo by Spd1 is unrelated to R2 subcellular localization. Finally, we identify a new behavior for RNR complexes that potentially provides yet another mechanism to regulate dNTP synthesis via modulation of RNR complex architecture.

In Schizosaccharomyces pombe the 14-3-3 protein Rad24p is involved in negative control of pho1 gene expression.

Expression of Schizosaccharomyces pombe pho1-encoded acid phosphatase is transcriptionally regulated by adenine and phosphate. Four genes, anr1-3 and anr5, encode negative regulators of pho1 expression. Apart from being designated as loci, the anr genes have not been further characterized. In this study we provide evidence that a strain carrying the deletion of rad24, a 14-3-3 protein-encoding gene, exhibits an anr mutant like the phenotype (higher phosphatase activity, higher transcript levels of pho1, lower sensitivity to adenine of pho1 expression) and that rad24 is closely linked, probably allelic, to anr5. By sequencing the two exons of the rad24 gene in a strain carrying the mutant allele anr5-13, we found a T/A-to-C/G transition in the 225th codon of its ORF, causing a leucine-to-serine substitution in a highly conserved region of all proteins of the 14-3-3 family. anr2 and anr3 are not allelic to rad24. The mutant alleles of anr2 and anr3 are recessive to their wild-type alleles and do not belong to the same epistasis group as rad24.

Transactivation of Schizosaccharomyces pombe cdt2+ stimulates a Pcu4-Ddb1-CSN ubiquitin ligase.

Cullin-4 forms a scaffold for multiple ubiquitin ligases. In Schizosaccharomyces pombe, the Cullin-4 homologue (Pcu4) physically associates with Ddb1 and the COP9 signalosome (CSN). One target of this complex is Spd1. Spd1 regulates ribonucleotide reductase (RNR) activity. Spd1 degradation during S phase, or following DNA damage of G2 cells, results in the nuclear export of the small RNR subunit. We demonstrate that Cdt2, an unstable WD40 protein, is a regulatory subunit of Pcu4-Ddb1-CSN ubiquitin ligase. cdt2 deletion stabilises Spd1 and prevents relocalisation of the small RNR subunit from the nucleus to the cytoplasm. cdt2+ is periodically transcribed by the Cdc10/DSC1 transcription factor during S phase and transiently transcribed following DNA damage of G2 cells, corresponding to Spd1 degradation profiles. Cdt2 co-precipitates with Spd1, and Cdt2 overexpression results in constitutive Spd1 degradation. We propose that Cdt2 incorporation into the Pcu4-Ddb1-CSN complex prompts Spd1 targeting and subsequent degradation and that Cdt2 is a WD40 repeat adaptor protein for Cullin-4-based ubiquitin ligase.

Chk1 activation requires Rad9 S/TQ-site phosphorylation to promote association with C-terminal BRCT domains of Rad4TOPBP1.

To gain insight into the function and organization of proteins assembled on the DNA in response to genotoxic insult we investigated the phosphorylation of the Schizosaccharomyces pombe PCNA-like checkpoint protein Rad9. C-terminal T412/S423 phosphorylation of Rad9 by Rad3(ATR) occurs in S phase without replication stress. Rad3(ATR) and Tel1(ATM) phosphorylate these same residues, plus additional ones, in response to DNA damage. In S phase and after damage, only Rad9 phosphorylated on T412/S423, but not unphosphorylated Rad9, associates with a two-BRCT-domain region of the essential Rad4(TOPBP1) protein. Rad9-Rad4(TOPBP1) interaction is required to activate the Chk1 damage checkpoint but not the Cds1 replication checkpoint. When the Rad9-T412/S423 are phosphorylated, Rad4(TOPBP1) coprecipitates with Rad3(ATR), suggesting that phosphorylation coordinates formation of an active checkpoint complex.

Delineating the position of rad4+/cut5+ within the DNA-structure checkpoint pathways in Schizosaccharomyces pombe.

The fission yeast BRCT domain protein Rad4/Cut5 is required for genome integrity checkpoint responses and DNA replication. Here we address the position at which Rad4/Cut5 acts within the checkpoint response pathways. Rad4 is shown to act upstream of the effector kinases Chk1 and Cds1, as both Chk1 phosphorylation and Cds1 kinase activity require functional Rad4. Phosphorylation of Rad9, Rad26 and Hus1 in response to either DNA damage or inhibition of DNA replication are independent of Rad4/Cut5 checkpoint function. Further we show that a novel, epitope-tagged allele of rad4+/cut5+ acts as a dominant suppressor of the checkpoint deficiencies of rad3-, rad26- and rad17- mutants. Suppression results in the restoration of mitotic arrest and is dependent upon the remaining checkpoint Rad proteins and the two effector kinases. High-level expression of the rad4+/cut5+ allele in rad17 mutant cells restores the nuclear localization of Rad9, but this does not fully account for the observed suppression. We conclude from these data that Rad4/Cut5 acts with Rad3, Rad26 and Rad17 to effect the checkpoint response, and a model for its function is discussed.

Inositol is specifically involved in the sexual program of the fission yeast Schizosaccharomyces pombe.

The fission yeast Schizosaccharomyces pombe is a natural auxotroph for inositol and fails to grow in the complete absence of it. It was previously reported that a small concentration of inositol in the culture medium supports vegetative growth, but not mating and sporulation, and a tenfold of that concentration also supports mating and sporulation. The purpose of the present work was to investigate whether a moderate inositol starvation specifically affected events of the sexual program of development. A homothallic culture grown to the stationary phase in medium with a small inositol concentration was sterile but cells in the stationary phase of growth synchronously entered and completed the sexual cycle when inositol was added, without need of previous cell divisions. This suggests the involvement of inositol in a mechanism (or mechanisms) of the sexual program. The events of the program that were affected by inositol starvation were investigated. Commitment to mating and production of pheromone M were shown not to be inositol-dependent. A diploid strain homozygous at the mating-type locus and carrying a pat1-114 temperature-sensitive mutation in homozygous configuration sporulated under inositol starvation at the restrictive temperature; therefore starvation did not directly affect meiosis or sporulation. In contrast, production of pheromone P and the response of cells to pheromones were found to be inositol-dependent. The possibility that inositol or one of its derivative compounds is involved in pheromone P secretion and in pheromone signal reception is discussed.