SIN-3 acts in distinct complexes to regulate the germline transcriptional program in Caenorhabditis elegans

The transcriptional co-regulator SIN3 influences gene expression through multiple interactions that include histone deacetylases. Haploinsufficiency and mutations in SIN3 are the underlying cause of Witteveen-Kolk syndrome and related intellectual disability and autism syndromes, emphasizing its key role in development. However, little is known about the diversity of its interactions and functions in developmental processes. Here, we show that loss of SIN-3, the single SIN3 homolog in Caenorhabditis elegans, results in maternal-effect sterility associated with de-regulation of the germline transcriptome, including de-silencing of X-linked genes. We identify at least two distinct SIN3 complexes containing specific histone deacetylases and show that they differentially contribute to fertility. Single-cell, single-molecule fluorescence in situ hybridization reveals that in sin-3 mutants the X chromosome becomes re-expressed prematurely and in a stochastic manner in individual germ cells, suggesting a role for SIN-3 in its silencing. Furthermore, we identify histone residues whose acetylation increases in the absence of SIN-3. Together, this work provides a powerful framework for the in vivo study of SIN3 and associated proteins.

Loss of SET1/COMPASS methyltransferase activity reduces lifespan and fertility in Caenorhabditis elegans

Changes in histone post-translational modifications are associated with aging through poorly defined mechanisms. Histone 3 lysine 4 (H3K4) methylation at promoters is deposited by SET1 family methyltransferases acting within conserved multiprotein complexes known as COMPASS. Previous work yielded conflicting results about the requirement for H3K4 methylation during aging. Here, we reassessed the role of SET1/COMPASS-dependent H3K4 methylation in Caenorhabditis elegans lifespan and fertility by generating set-2(syb2085) mutant animals that express a catalytically inactive form of SET-2, the C. elegans SET1 homolog. We show that set-2(syb2085) animals retain the ability to form COMPASS, but have a marked global loss of H3K4 di- and trimethylation (H3K4me2/3). Reduced H3K4 methylation was accompanied by loss of fertility, as expected; however, in contrast to earlier studies, set-2(syb2085) mutants displayed a significantly shortened, not extended, lifespan and had normal intestinal fat stores. Other commonly used set-2 mutants were also short-lived, as was a cfp-1 mutant that lacks the SET1/COMPASS chromatin-targeting component. These results challenge previously held views and establish that WT H3K4me2/3 levels are essential for normal lifespan in C. elegans.

Auxin confers protection against ER stress in Caenorhabditis elegans

Auxins are plant growth regulators that influence most aspects of plant development through complex mechanisms. The development of an auxin-inducible degradation (AID) system has enabled rapid, conditional protein depletion in yeast and cultured cells. More recently, the system was successfully adapted to Caenorhabditiselegans to achieve auxin-dependent degradation of targets in all tissues and developmental stages. Whether auxin treatment alone has an impact on nematode physiology is an open question. Here we show that indole-3-acetic acid (IAA), the auxin most commonly used to trigger AID in worms, functions through the conserved IRE-1/XBP-1 branch of the Unfolded Protein Response (UPR) to promote resistance to endoplasmic reticulum (ER) stress. Because the UPR not only plays a central role in restoring ER homeostasis, but also promotes lipid biosynthesis and regulates lifespan, we suggest that extreme caution should be exercised when using the AID system to study these and related processes.

Summary: Auxin, commonly used to induce conditional protein degradation, promotes ER stress resistance in C. elegans through the unfolded protein response (UPR).

RNA polymerase II CTD S2P is dispensable for embryogenesis but mediates exit from developmental diapause in C. elegans

Serine 2 phosphorylation (S2P) within the CTD of RNA polymerase II is considered a Cdk9/Cdk12-dependent mark required for 3'-end processing. However, the relevance of CTD S2P in metazoan development is unknown. We show that cdk-12 lesions or a full-length CTD S2A substitution results in an identical phenotype in Caenorhabditis elegans Embryogenesis occurs in the complete absence of S2P, but the hatched larvae arrest development, mimicking the diapause induced when hatching occurs in the absence of food. Genome-wide analyses indicate that when CTD S2P is inhibited, only a subset of growth-related genes is not properly expressed. These genes correspond to SL2 trans-spliced mRNAs located in position 2 and over within operons. We show that CDK-12 is required for maximal occupancy of cleavage stimulatory factor necessary for SL2 trans-splicing. We propose that CTD S2P functions as a gene-specific signaling mark ensuring the nutritional control of the C. elegans developmental program.

Caenorhabditis elegans SET1/COMPASS Maintains Germline Identity by Preventing Transcriptional Deregulation Across Generations

Chromatin regulators contribute to the maintenance of the germline transcriptional program. In the absence of SET-2, the Caenorhabditis elegans homolog of the SET1/COMPASS H3 Lys4 (H3K4) methyltransferase, animals show transgenerational loss of germline identity, leading to sterility. To identify transcriptional signatures associated with progressive loss of fertility, we performed expression profiling of set-2 mutant germlines across generations. We identify a subset of genes whose misexpression is first observed in early generations, a step we refer to as priming; their misexpression then further progresses in late generations, as animals reach sterility. Analysis of misregulated genes shows that down-regulation of germline genes, expression of somatic transcriptional programs, and desilencing of the X-chromosome are concurrent events leading to loss of germline identity in both early and late generations. Upregulation of transcription factor LIN-15B, the C/EBP homolog CEBP-1, and TGF-β pathway components strongly contribute to loss of fertility, and RNAi inactivation of cebp-1 and TGF-β/Smad signaling delays the onset of sterility, showing they individually contribute to maintenance of germ cell identity. Our approach therefore identifies genes and pathways whose misexpression actively contributes to the loss of germ cell fate. More generally, our data shows how loss of a chromatin regulator in one generation leads to transcriptional changes that are amplified over subsequent generations, ultimately leading to loss of appropriate cell fate.

A Role for Caenorhabditis elegans COMPASS in Germline Chromatin Organization

Deposition of histone H3 lysine 4 (H3K4) methylation at promoters is catalyzed by the SET1/COMPASS complex and is associated with context-dependent effects on gene expression and local changes in chromatin organization. The role of SET1/COMPASS in shaping chromosome architecture has not been investigated. Here we used Caenorhabditis elegans to address this question through a live imaging approach and genetic analysis. Using quantitative FRET (Förster resonance energy transfer)-based fluorescence lifetime imaging microscopy (FLIM) on germ cells expressing histones eGFP-H2B and mCherry-H2B, we find that SET1/COMPASS influences meiotic chromosome organization, with marked effects on the close proximity between nucleosomes. We further show that inactivation of set-2, encoding the C. elegans SET1 homologue, or CFP-1, encoding the chromatin targeting subunit of COMPASS, enhances germline chromosome organization defects and sterility of condensin-II depleted animals. set-2 loss also aggravates germline defects resulting from conditional inactivation of topoisomerase II, another structural component of chromosomes. Expression profiling of set-2 mutant germlines revealed only minor transcriptional changes, suggesting that the observed effects are at least partly independent of transcription. Altogether, our results are consistent with a role for SET1/COMPASS in shaping meiotic chromosomes in C. elegans, together with the non-histone proteins condensin-II and topoisomerase. Given the high degree of conservation, our findings expand the range of functions attributed to COMPASS and suggest a broader role in genome organization in different species.

Physical and functional interaction between SET1/COMPASS complex component CFP-1 and a Sin3S HDAC complex in C. elegans

The CFP1 CXXC zinc finger protein targets the SET1/COMPASS complex to non-methylated CpG rich promoters to implement tri-methylation of histone H3 Lys4 (H3K4me3). Although H3K4me3 is widely associated with gene expression, the effects of CFP1 loss vary, suggesting additional chromatin factors contribute to context dependent effects. Using a proteomics approach, we identified CFP1 associated proteins and an unexpected direct link between Caenorhabditis elegans CFP-1 and an Rpd3/Sin3 small (SIN3S) histone deacetylase complex. Supporting a functional connection, we find that mutants of COMPASS and SIN3 complex components genetically interact and have similar phenotypic defects including misregulation of common genes. CFP-1 directly binds SIN-3 through a region including the conserved PAH1 domain and recruits SIN-3 and the HDA-1/HDAC subunit to H3K4me3 enriched promoters. Our results reveal a novel role for CFP-1 in mediating interaction between SET1/COMPASS and a Sin3S HDAC complex at promoters.

'Frequently recurring' nocturnal polyuria is predictive of response to desmopressin in monosymptomatic nocturnal enuresis in childhood

INTRODUCTION

The nocturnal polyuria is considered a significant predictive value for response to desmopressin. The cutoff value useful to define nocturnal polyuria is still a matter of debate. Moreover, it is current notion that maximal voided volume (MVV) could be used as a predictor for desmopressin response.

OBJECTIVE

The objective of this study was to assess the impact of different definitions of nocturnal polyuria (and of its frequency) and MVV in predicting the response to desmopressin.

STUDY DESIGN

A total of 103 patients with frequent monosymptomatic nocturnal enuresis (≥4 wet nights/week) were enrolled. A bladder diary over a 4-day period was collected. The MVV was defined as the highest micturition volume detected at bladder diary. Nocturnal diuresis was measured in 5 wet nights. Then, patients were administered with 120 mcg of sublingual desmopressin. After 2 months, if there was no complete response, the dose was increased to 240 mcg. Nocturnal polyuria was defined as follows: 1.Definition 1: nocturnal urine production >130% of the expected bladder capacity (EBC). 2. Definition 2: >100% EBC. 3. Definition 3: > 20×(age + 9) mL. The primary outcome was 'response to desmopressin' after 3 months of treatment.

RESULTS

Fifty-three patients responded to desmopressin. Comparing the responses to desmopressin on the basis of the three definitions of nocturnal polyuria, no significant difference was found. There was no cutoff value of nocturnal polyuria expressed as %EBC useful in providing a significant receiver-operating characteristic (ROC) curve. The area under the ROC curve for MVV expressed as %EBC was 0.67 (95% confidence interval [CI], 0.54-0.80; p = 0.01). A MVV >103.1% of EBC had 78.8% (95% CI, 61.1-91.0) sensitivity and 47.5% (95% CI, 31.5-63.9) specificity for predicting response to desmopressin. Among the patients with nocturnal polyuria according to definition 1, a higher percentage of subjects with nocturnal polyuria in 4 out of 5 or 5 out of 5 nights responded to desmopressin, compared with other patients. Patients presenting with nocturnal polyuria according to definition 3 in 5 out of 5 nights showed a 100% of response to desmopressin. At multivariate analysis, the only significant odds ratio (OR) to respond to desmopressin was that of patients with nocturnal polyuria according to definition 1 in >3 nights (OR = 7.1, 95% CI, 1.3-40.3).

DISCUSSION AND CONCLUSIONS

The presence or absence of nocturnal polyuria-according to all three definitions-in at least one night was not effective in predicting the response to desmopressin. Predictors of desmopressin response were nocturnal polyuria in >3 out of 5 wet nights according to definition 1 and in 5 out of 5 wet nights according to definition 3.

Adaptive preconditioning in neurological diseases - therapeutic insights from proteostatic perturbations

In neurological disorders, both acute and chronic neural stress can disrupt cellular proteostasis, resulting in the generation of pathological protein. However in most cases, neurons adapt to these proteostatic perturbations by activating a range of cellular protective and repair responses, thus maintaining cell function. These interconnected adaptive mechanisms comprise a 'proteostasis network' and include the unfolded protein response, the ubiquitin proteasome system and autophagy. Interestingly, several recent studies have shown that these adaptive responses can be stimulated by preconditioning treatments, which confer resistance to a subsequent toxic challenge - the phenomenon known as hormesis. In this review we discuss the impact of adaptive stress responses stimulated in diverse human neuropathologies including Parkinson׳s disease, Wolfram syndrome, brain ischemia, and brain cancer. Further, we examine how these responses and the molecular pathways they recruit might be exploited for therapeutic gain. This article is part of a Special Issue entitled SI:ER stress.

Repression of somatic cell fate in the germline

Germ cells must transmit genetic information across generations, and produce gametes while also maintaining the potential to form all cell types after fertilization. Preventing the activation of somatic programs is, therefore, crucial to the maintenance of germ cell identity. Studies in Caenorhabditis elegans, Drosophila melanogaster, and mouse have revealed both similarities and differences in how somatic gene expression is repressed in germ cells, thereby preventing their conversion into somatic tissues. This review will focus on recent developments in our understanding of how global or gene-specific transcriptional repression, chromatin regulation, and translational repression operate in the germline to maintain germ cell identity and repress somatic differentiation programs.

Genome-wide screen identifies a novel p97/CDC-48-dependent pathway regulating ER-stress-induced gene transcription

The accumulation of misfolded proteins in the endoplasmic reticulum (ER) activates the Unfolded Protein Response (UPR(ER)) to restore ER homeostasis. The AAA(+) ATPase p97/CDC-48 plays key roles in ER stress by promoting both ER protein degradation and transcription of UPR(ER) genes. Although the mechanisms associated with protein degradation are now well established, the molecular events involved in the regulation of gene transcription by p97/CDC-48 remain unclear. Using a reporter-based genome-wide RNAi screen in combination with quantitative proteomic analysis in Caenorhabditis elegans, we have identified RUVB-2, a AAA(+) ATPase, as a novel repressor of a subset of UPR(ER) genes. We show that degradation of RUVB-2 by CDC-48 enhances expression of ER stress response genes through an XBP1-dependent mechanism. The functional interplay between CDC-48 and RUVB-2 in controlling transcription of select UPR(ER) genes appears conserved in human cells. Together, these results describe a novel role for p97/CDC-48, whereby its role in protein degradation is integrated with its role in regulating expression of ER stress response genes.

The SET-2/SET1 histone H3K4 methyltransferase maintains pluripotency in the Caenorhabditis elegans germline

Histone H3 Lys 4 methylation (H3K4me) is deposited by the conserved SET1/MLL methyltransferases acting in multiprotein complexes, including Ash2 and Wdr5. Although individual subunits contribute to complex activity, how they influence gene expression in specific tissues remains largely unknown. In Caenorhabditis elegans, SET-2/SET1, WDR-5.1, and ASH-2 are differentially required for germline H3K4 methylation. Using expression profiling on germlines from animals lacking set-2, ash-2, or wdr-5.1, we show that these subunits play unique as well as redundant functions in order to promote expression of germline genes and repress somatic genes. Furthermore, we show that in set-2- and wdr-5.1-deficient germlines, somatic gene misexpression is associated with conversion of germ cells into somatic cells and that nuclear RNAi acts in parallel with SET-2 and WDR-5.1 to maintain germline identity. These findings uncover a unique role for SET-2 and WDR-5.1 in preserving germline pluripotency and underline the complexity of the cellular network regulating this process.

C. elegans epigenetic regulation in development and aging

The precise developmental map of the Caenorhabditis elegans cell lineage, as well as a complete genome sequence and feasibility of genetic manipulation make this nematode species highly attractive to study the role of epigenetics during development. Genetic dissection of phenotypical traits, such as formation of egg-laying organs or starvation-resistant dauer larvae, has illustrated how chromatin modifiers may regulate specific cell-fate decisions and behavioral programs. Moreover, the transparent body of C. elegans facilitates non-invasive microscopy to study tissue-specific accumulation of heterochromatin at the nuclear periphery. We also review here recent findings on how small RNA molecules contribute to epigenetic control of gene expression that can be propagated for several generations and eventually determine longevity.

Endogenous nuclear RNAi mediates behavioral adaptation to odor

Most eukaryotic cells express small regulatory RNAs. The purpose of one class, the somatic endogenous siRNAs (endo-siRNAs), remains unclear. Here, we show that the endo-siRNA pathway promotes odor adaptation in C. elegans AWC olfactory neurons. In adaptation, the nuclear Argonaute NRDE-3, which acts in AWC, is loaded with siRNAs targeting odr-1, a gene whose downregulation is required for adaptation. Concomitant with increased odr-1 siRNA in AWC, we observe increased binding of the HP1 homolog HPL-2 at the odr-1 locus in AWC and reduced odr-1 mRNA in adapted animals. Phosphorylation of HPL-2, an in vitro substrate of the EGL-4 kinase that promotes adaption, is necessary and sufficient for behavioral adaptation. Thus, environmental stimulation amplifies an endo-siRNA negative feedback loop to dynamically repress cognate gene expression and shape behavior. This class of siRNA may act broadly as a rheostat allowing prolonged stimulation to dampen gene expression and promote cellular memory formation. PAPERFLICK:

Transgenerational functions of small RNA pathways in controlling gene expression in C. elegans

RNA silencing processes use exogenous or endogenous RNA molecules to specifically and robustly regulate gene expression. In C. elegans, initial mechanistic descriptions of the different silencing processes focused on posttranscriptional regulation. In this review, we discuss recent work showing that, in this model organism, RNA silencing also controls the transcription of target genes by inducing heterochromatin formation. Specifically, it has been shown that ribonucleoprotein complexes containing small RNAs, either processed from exogenous dsRNA or synthesized from the genome itself, and proteins of the Argonaute family, mediate the deposition of repressive histone marks at the targeted loci. Interestingly, the accumulation of repressive marks is required for the inheritance of the silencing effect and the establishment of an epigenetic memory that discriminates self- from non-self-RNAs.

Caenorhabditis elegans Heterochromatin protein 1 (HPL-2) links developmental plasticity, longevity and lipid metabolism

Background

Heterochromatin protein 1 (HP1) family proteins have a well-characterized role in heterochromatin packaging and gene regulation. Their function in organismal development, however, is less well understood. Here we used genome-wide expression profiling to assess novel functions of the Caenorhabditis elegans HP1 homolog HPL-2 at specific developmental stages.

Results

We show that HPL-2 regulates the expression of germline genes, extracellular matrix components and genes involved in lipid metabolism. Comparison of our expression data with HPL-2 ChIP-on-chip profiles reveals that a significant number of genes up- and down-regulated in the absence of HPL-2 are bound by HPL-2. Germline genes are specifically up-regulated in hpl-2 mutants, consistent with the function of HPL-2 as a repressor of ectopic germ cell fate. In addition, microarray results and phenotypic analysis suggest that HPL-2 regulates the dauer developmental decision, a striking example of phenotypic plasticity in which environmental conditions determine developmental fate. HPL-2 acts in dauer at least partly through modulation of daf-2/IIS and TGF-β signaling pathways, major determinants of the dauer program. hpl-2 mutants also show increased longevity and altered lipid metabolism, hallmarks of the long-lived, stress resistant dauers.

Conclusions

Our results suggest that the worm HP1 homologue HPL-2 may coordinately regulate dauer diapause, longevity and lipid metabolism, three processes dependent on developmental input and environmental conditions. Our findings are of general interest as a paradigm of how chromatin factors can both stabilize development by buffering environmental variation, and guide the organism through remodeling events that require plasticity of cell fate regulation.

Epigenetics in C. elegans: facts and challenges

Epigenetics is defined as the study of heritable changes in gene expression that are not accompanied by changes in the DNA sequence. Epigenetic mechanisms include histone post-translational modifications, histone variant incorporation, non-coding RNAs, and nucleosome remodeling and exchange. In addition, the functional compartmentalization of the nucleus also contributes to epigenetic regulation of gene expression. Studies on the molecular mechanisms underlying epigenetic phenomena and their biological function have relied on various model systems, including yeast, plants, flies, and cultured mammalian cells. Here we will expose the reader to the current understanding of epigenetic regulation in the roundworm C. elegans. We will review recent models of nuclear organization and its impact on gene expression, the biological role of enzymes modifying core histones, and the function of chromatin-associated factors, with special emphasis on Polycomb (PcG) and Trithorax (Trx-G) group proteins. We will discuss how the C. elegans model has provided novel insight into mechanisms of epigenetic regulation as well as suggest directions for future research.

Perinuclear distribution of heterochromatin in developing C. elegans embryos

Specific nuclear domains are nonrandomly positioned within the nuclear space, and this preferential positioning has been shown to play an important role in genome activity and stability. Well-known examples include the organization of repetitive DNA in telomere clusters or in the chromocenter of Drosophila and mammalian cells, which may provide a means to control the availability of general repressors, such as the heterochromatin protein 1 (HP1). We have specifically characterized the intranuclear positioning of in vivo fluorescence of the Caenorhabditis elegans HP1 homologue HPL-2 as a marker for heterochromatin domains in developing embryos. For this purpose, the wavelet transform modulus maxima (WTMM) segmentation method was generalized and adapted to segment the small embryonic cell nuclei in three dimensions. The implementation of a radial distribution algorithm revealed a preferential perinuclear positioning of HPL-2 fluorescence in wild-type embryos compared with the diffuse and homogeneous nuclear fluorescence observed in the lin-13 mutants. For all other genotypes analyzed, the quantitative analysis highlighted various degrees of preferential HPL-2 positioning at the nuclear periphery, which directly correlates with the number of HPL-2 foci previously counted on 2D projections. Using a probabilistic 3D cell nuclear model, we found that any two nuclei having the same number of foci, but with a different 3D probabilistic positioning scheme, can have significantly different counts in the 2D maximum projection, thus showing the deceptive limitations of using techniques of 2D maximum projection foci counts. By this approach, a strong perinuclear positioning of HPL-2 foci was brought into light upon inactivation of conserved chromatin-associated proteins, including the HAT cofactor TRAPP.

A novel role for the SMG-1 kinase in lifespan and oxidative stress resistance in Caenorhabditis elegans

The PTEN tumour suppressor encodes a phosphatase, and its daf-18 orthologue in Caenorhabditis elegans negatively regulates the insulin/IGF-1 DAF-2 receptor pathway that influences lifespan in worms and other species. In order to identify new DAF-18 regulated pathways involved in aging, we initiated a candidate RNAi feeding screen for clones that lengthen lifespan. Here, we report that smg-1 inactivation increases average lifespan in a daf-18 dependent manner. Genetic analysis is consistent with SMG-1 acting at least in part in parallel to the canonical DAF-2 receptor pathway, but converging on the transcription factor DAF-16/FOXO. SMG-1 is a serine-threonine kinase which plays a conserved role in nonsense-mediated mRNA decay (NMD) in worms and mammals. In addition, human SMG-1 has also been implicated in the p53-mediated response to genotoxic stress. The effect of smg-1 inactivation on lifespan appears to be unrelated to its NMD function, but requires the p53 tumour suppressor orthologue cep-1. Furthermore, smg-1 inactivation confers a resistance to oxidative stress in a daf-18-, daf-16- and cep-1-dependent manner. We propose that the role of SMG-1 in lifespan regulation is at least partly dependent on its function in oxidative stress resistance. Taken together, our results unveil a novel role for SMG-1 in lifespan regulation.

Antagonistic functions of SET-2/SET1 and HPL/HP1 proteins in C. elegans development

Cellular identity during metazoan development is maintained by epigenetic modifications of chromatin structure brought about by the activity of specific proteins which mediate histone variant incorporation, histone modifications, and nucleosome remodeling. HP1 proteins directly influence gene expression by modifying chromatin structure. We previously showed that the Caenorhabditis elegans HP1 proteins HPL-1 and HPL-2 are required for several aspects of post-embryonic development. To gain insight into how HPL proteins influence gene expression in a developmental context, we carried out a candidate RNAi screen to identify suppressors of hpl-1 and hpl-2 phenotypes. We identified SET-2, the homologue of yeast and mammalian SET1, as an antagonist of HPL-1 and HPL-2 activity in growth and somatic gonad development. Yeast Set1 and its mammalian counterparts SET1/MLL are H3 lysine 4 (H3K4) histone methyltransferases associated with gene activation as part of large multisubunit complexes. We show that the nematode counterparts of SET1/MLL complex subunits also antagonize HPL function in post-embryonic development. Genetic analysis is consistent with SET1/MLL complex subunits having both shared and unique functions in development. Furthermore, as observed in other species, we find that SET1/MLL complex homologues differentially affect global H3K4 methylation. Our results suggest that HP1 and a SET1/MLL-related complex may play antagonistic roles in the epigenetic regulation of specific developmental programs.

Unique and redundant functions of C. elegans HP1 proteins in post-embryonic development

HP1 proteins are essential components of heterochromatin and contribute to the transcriptional repression of euchromatic genes. Although most species contain more than one HP1 family member which differ in their chromosomal distribution, it is not known to what extent the activity of these different family members is redundant or specific in a developmental context. C. elegans has two HP1 homologues, HPL-1 and HPL-2. While HPL-2 functions in vulval and germline development, no function has so far been attributed to HPL-1. Here we report the characterization of an hpl-1 null allele. We show that while the absence of hpl-1 alone results in no obvious phenotype, hpl-1;hpl-2 double mutants show synthetic, temperature sensitive phenotypes including larval lethality and severe defects in the development of the somatic gonad. Furthermore, we find that hpl-1 has an unexpected role in vulval development by acting redundantly with hpl-2, but not other genes previously implicated in vulval development. Localization studies show that like HPL-2, HPL-1 is a ubiquitously expressed nuclear protein. However, HPL-1 and HPL-2 localization does not completely overlap. Our results show that HPL-1 and HPL-2 play both unique and redundant functions in post-embryonic development.

The C. elegans HP1 homologue HPL-2 and the LIN-13 zinc finger protein form a complex implicated in vulval development

HP1 proteins are essential components of heterochromatin and contribute to the transcriptional repression of euchromatic genes via the recruitment to specific promoters by corepressor proteins including TIF1 and Rb. The Caenorhabditis elegans HP1 homologue HPL-2 acts in the "synMuv" (synthetic multivulval) pathway, which defines redundant negative regulators of a Ras signaling cascade required for vulval induction. Several synMuv genes encode for chromatin-associated proteins involved in transcriptional regulation, including Rb and components of the Mi-2/NuRD and TIP60/NuA4 chromatin remodeling complexes. Here, we show that HPL-2 physically interacts in vitro and in vivo with the multiple zinc finger protein LIN-13, another member of the synMuv pathway. A variant of the conserved PXVXL motif found in many HP1-interacting proteins mediates LIN-13 binding to the CSD of HPL-2. We further show by in vivo localization studies that LIN-13 is required for HPL-2 recruitment in nuclear foci. Our data suggest that the LIN-13/HPL-2 complex may physically link a subset of the Rb related synMuv proteins to chromatin.

A heterochromatin protein 1 homologue in Caenorhabditis elegans acts in germline and vulval development

Proteins of the highly conserved heterochromatin protein 1 (HP1) family have been found to function in the dynamic organization of nuclear architecture and in gene regulation throughout the eukaryotic kingdom. In addition to being key players in heterochromatin-mediated gene silencing, HP1 proteins may also contribute to the transcriptional repression of euchromatic genes via the recruitment to specific promoters. To investigate the role played by these different activities in specific developmental pathways, we identified HP1 homologues in the genome of Caenorhabditis elegans and used RNA-mediated interference to study their function. We show that one of the homologues, HPL-2, is required for the formation of a functional germline and for the development of the vulva by acting in an Rb-related pathway. We suggest that, by acting as repressors of gene expression, HP1 proteins may fulfil specific functions in both somatic and germline differentiation processes throughout development.

MRI assessment of ventricular function

Cine-MRI is a robust non invasive technique able to assess regional and global systolic function of both ventricles. Conventinal cine-MRI was used for LV global function parameters both on horizontal long axis and vertical long axis, applying area-length methods, as in echocardiography. Recent developments of segmented k-space techniques allowed breath-held cine-MRI, making possible a rapid acquisition of the entire ventricles, both left and right. Using the Simpson's rule volumes are estimated with high accuracy, without any geometrical assumption; this method is considered gold standard for global function assessment. Regional function is studied by cine-MRI both qualitatively and quantitatively, as it represents the best technique in defining endo- and epi-cardial borders. The ability of quantify wall thickness and wall thickening makes cine-MRI highly suitable for stress-imaging, both in ischemia detection and viability assessment. Tagging is a novel technique, able to assess the complex mechanism of myocardial contraction and to quantify myocardial strain. Finally MRI is also able to assess diastolic function with phase velocity mapping.

The C. elegans Mi-2 chromatin-remodelling proteins function in vulval cell fate determination

The Mi-2 protein is the central component of the recently isolated NuRD nucleosome remodelling and histone deacetylase complex. Although the NuRD complex has been the subject of extensive biochemical analyses, little is known about its biological function. Here we show that the two C. elegans Mi-2 homologues, LET-418 and CHD-3, play essential roles during development. The two proteins possess both shared and unique functions during vulval cell fate determination, including antagonism of the Ras signalling pathway required for vulval cell fate induction and the proper execution of the 2 degrees cell fate of vulval precursor cells, a process under the control of LIN-12 Notch signalling.

Endoscopic pancreatic stenting in pancreatic cancer

Most pancreatic carcinomas are unresectable at the time of diagnosis; therefore, palliative treatment is very often the main concern of clinicians in this setting. The main symptoms resulting in the need for palliation in pancreatic cancer are obstructive jaundice, duodenal obstruction and pain. Therapeutic endoscopy plays a major role in the palliation of obstructive jaundice by stent placement into the biliary ducts. Initial experience has also been gained recently with endoscopic placement of expandable metallic stents to treat gastric outlet obstruction. Much less is known about the possible role of endoscopic pancreatic stenting in patients with unresectable pancreatic carcinoma. The main indication for pancreatic ductal stenting is 'obstructive' pain related to meals in patients with dilated main pancreatic duct beyond the stricture and intraluminal brachyradiotherapy. The technique of endoscopic pancreatic stenting does not substantially differ from that applied on the biliary tree. When technically possible, placement of 10 French plastic stents is preferred. According to the authors' indications, only about 15% of patients with advanced pancreatic cancer (55 of 355 in the present study) may potentially benefit from this technique. Pancreatic stenting may be obtained in more than 80% of these selected patients, with low morbidity (less than 10%) and no procedure-related mortality. According to the authors of the present and other studies reported in the literature, about 60% of patients treated because of 'obstructive' pain become symptom-free, and another 20% to 25% significantly reduce the amount of analgesic drugs required. Intraluminal brachyradiotherapy with 192iridium in the main pancreatic duct is a feasible and safe method to deliver high radiation doses to the tumour while sparing adjacent organs. Brachyradiotherapy may be performed alone or in conjunction with external beam radiotherapy. Because of the small number of patients suitable for this treatment, only a multicentre study will be able to detect whether intraluminal brachyradiotherapy in pancreatic cancer may have any positive impact on survival.

Functional characterization of the N terminus of Sir3p

Silent information regulator 3 is an essential component of the Saccharomyces cerevisiae silencing complex that functions at telomeres and the silent mating-type loci, HMR and HML. We show that expression of the N- and C-terminal-encoding halves of SIR3 in trans partially complements the mating defect of the sir3 null allele, suggesting that the two domains have distinct functions. We present here a functional characterization of these domains. The N-terminal domain (Sir3N) increases both the frequency and extent of telomere-proximal silencing when expressed ectopically in SIR+ yeast strains, although we are unable to detect interaction between this domain and any known components of the silencing machinery. In contrast to its effect at telomeres, Sir3N overexpression derepresses transcription of reporter genes inserted in the ribosomal DNA (rDNA) array. Immunolocalization of Sir3N-GFP and Sir2p suggests that Sir3N directly antagonizes nucleolar Sir2p, releasing an rDNA-bound population of Sir2p so that it can enhance repression at telomeres. Overexpression of the C-terminal domain of either Sir3p or Sir4p has a dominant-negative effect on telomeric silencing. In strains overexpressing the C-terminal domain of Sir4p, elevated expression of either full-length Sir3p or Sir3N restores repression and the punctate pattern of Sir3p and Rap1p immunostaining. The similarity of Sir3N and Sir3p overexpression phenotypes suggests that Sir3N acts as an allosteric effector of Sir3p, either enhancing its interactions with other silencing components or liberating the full-length protein from nonfunctional complexes.

[Immediate reocclusion of the infrapopliteal segment after thrombolysis in acute ischemia of the lower limb of the thrombotic nature]

Early reocclusion of below knee segment after fibrinolytic therapy is mainly due to thrombo-embolism, coagulopathy or to the arterial wall condition. 42 patients facing acute lower limb ischaemia because of iliofemoral thrombosis (prosthesis 19, native artery 23) underwent locoregional thrombolysis. UK was given in 33 cases while the others received rt-PA. The early reocclusion after fibrinolysis leads to a serious worsening in these patients; thrombosis in distal vessels and in microvasculature make any surgical approach unserviceable. Major amputation was required in 3 cases. We believe that fibrinolytic treatment has taken on great importance in making accurate diagnosing of thromboembolism and, once restored patency of distal vessels, allows to perform revascularization procedures.

The carboxy termini of Sir4 and Rap1 affect Sir3 localization: evidence for a multicomponent complex required for yeast telomeric silencing

The Silent Information Regulatory proteins, Sir3 and Sir4, and the telomeric repeat-binding protein RAP1 are required for the chromatin-mediated gene repression observed at yeast telomeric regions. All three proteins are localized by immunofluorescence staining to foci near the nuclear periphery suggesting a relationship between subnuclear localization and silencing. We present several lines of immunological and biochemical evidence that Sir3, Sir4, and RAP1 interact in intact yeast cells. First, immunolocalization of Sir3 to foci at the yeast nuclear periphery is lost in rap1 mutants carrying deletions for either the terminal 28 or 165 amino acids of RAP1. Second, the perinuclear localization of both Sir3 and RAP1 is disrupted by overproduction of the COOH terminus of Sir4. Third, overproduction of the Sir4 COOH terminus alters the solubility properties of both Sir3 and full-length Sir4. Finally, we demonstrate that RAP1 and Sir4 coprecipitate in immune complexes using either anti-RAP1 or anti-Sir4 antibodies. We propose that the integrity of a tertiary complex between Sir4, Sir3, and RAP1 is involved in both the maintenance of telomeric repression and the clustering of telomeres in foci near the nuclear periphery.

Telomere maintenance and gene repression: a common end?

In yeast, the study of the teleomere has recently provided new information on the requirements for chromosome stability, on elements influencing nuclear architecture and on position-effect variegation.

SIR3 and SIR4 proteins are required for the positioning and integrity of yeast telomeres

Heritable inactivation of genes occurs in specific chromosomal domains located at the silent mating type loci and at telomeres of S. cerevisiae. The SIR genes (for silent information regulators) are trans-acting factors required for this repression mechanism. We show here that the SIR3 and SIR4 gene products have a sub-nuclear localization similar to the telomere-associated RAP1 protein, which is found primarily in foci at the nuclear periphery of fixed yeast spheroplasts. In strains deficient for either SIR3 or SIR4, telomeres lose their perinuclear localization, as monitored by RAP1 immunofluorescence. The length of the telomeric repeat shortens in sir3 and sir4 mutant strains, and the mitotic stability of chromosome V is reduced. These data suggest that SIR3 and SIR4 are required for both the integrity and subnuclear localization of yeast telomeres, the loss of which correlates with loss of telomere-associated gene repression.

Analysis of mitotic and meiotic defects in Saccharomyces cerevisiae SRS2 DNA helicase mutants

The hyper-gene conversion srs2-101 mutation of the SRS2 DNA helicase gene of Saccharomyces cerevisiae has been reported to suppress the UV sensitivity of rad18 mutants. New alleles of SRS2 were recovered using this suppressor phenotype. The alleles have been characterized with respect to suppression of rad18 UV sensitivity, hyperrecombination, reduction of meiotic viability, and definition of the mutational change within the SRS2 gene. Variability in the degree of rad18 suppression and hyperrecombination were found. The alleles that showed the severest effects were found to be missense mutations within the consensus domains of the DNA helicase family of proteins. The effect of mutations in domains I (ATP-binding) and V (proposed DNA binding) are reported. Some alleles of SRS2 reduce spore viability to 50% of wild-type levels. This phenotype is not bypassed by spo13 mutation. Although the srs2 homozygous diploids strains undergo normal commitment to meiotic recombination, this event is delayed by several hours in the mutant strains and the strains appear to stall in the progression from meiosis I to meiosis II.

[Composite bypass using endarterectomized autologous superficial femoral artery. A valid concept in the extension of lower limb salvage surgery]

Saphenous vein is nowadays the material of choice performing on femoro-distal revascularisation; when this is not available, it is important to use a material which gives the closest approximation of an ideal conduit and for same time an easy handling during the execution of the anastomosis. Although vein's degenerative alterations are very rare, it has now been shown that there is widespread destruction of the endothelium among infrainguinal vein grafting, producing a relatively thrombogenic surface. These factors may contribute to the initial failure rate of these bypasses. For this reason we suggest to employ a segment of thromboendarterectomized SFA (superficial femoral artery) as a distal part of a composite bypass. Twenty-four composite bypasses were performed using three different methods over a total of 123 femoro-distal revascularizations. Eighteen months follow-up showed more than 50% and more than 75% patency rate comparing type B (graft or thromboendarterectomized SFA + autogenous saphenous vein) and type C (thromboendarterectomyied SFA + graft). We believe, waiting for a wider follow-up, that this technique could be a valid alternative to a femoro-distal revascularization when saphenous vein is not available.

The hyper-gene conversion hpr5-1 mutation of Saccharomyces cerevisiae is an allele of the SRS2/RADH gene

The HPR5 gene has been defined by the mutation hpr5-1 that results in an increased rate of gene conversion. This mutation suppresses the UV sensitive phenotype of rad18 mutations in hpr5-1 rad18 double mutants by channeling the aborted repair events into a recombination repair pathway. The HPR5 gene has been cloned and is shown to be allelic to the SRS2/RADH gene, a putative DNA helicase. The HPR5 gene, which is nonessential, is tightly linked to the ARG3 locus chromosome X. The hpr5-1 allele contains missense mutation in the putative ATP binding domain. A comparison of the recombination properties of the hpr5-1 allele and the null allele suggests that recombination events in hpr5 defective strains can be generated by several mechanisms. We propose that the HPR5 gene functions in the RAD6 repair pathway.

Neuropsychological assessment of functional central nervous system disorders. I. Hemispheric functioning characteristics in schizophrenia and affective illness

The neuropsychological characteristics of a group of schizophrenic and affective patients were assessed by mean of a comprehensive neuropsychological tool, the Luria-Nebraska Neuropsychological Batter (LNNB), to determine the lateralized hemispheric neurofunctional characteristics in major functional central nervous system disorders. The results showed that schizophrenics had more right-hemisphere impairment than affectives. They do not substantiate the hypothesis of right hemisphere-lateralized malfunctioning in functional mood disorders. Psychopharmacological treatment influences neuropsychological test performance, neuroleptics having the greatest effects. Pharmacological effects other than anticholinergic ones are responsible for the negative influence on neuropsychological test performance.

The adenovirus tripartite leader may eliminate the requirement for cap-binding protein complex during translation initiation

The adenovirus tripartite leader is a 200-nucleotide 5' noncoding region that is found on all late viral mRNAs. This segment is required for preferential translation of viral mRNAs at late times during infection. Most tripartite leader-containing mRNAs appear to exhibit little if any requirement for intact cap-binding protein complex, a property previously established only for uncapped poliovirus mRNAs and capped mRNAs with minimal secondary structure. The tripartite leader also permits the translation of mRNAs in poliovirus-infected cells in the apparent absence of active cap-binding protein complex and does not require any adenovirus gene products for this activity. The preferential translation of viral late mRNAs may involve this unusual property.

Aneurysm of the abdominal aorta in a young woman. Atherosclerotic or inflammatory in origin?

The case is described of a 27 year old woman with aneurysms of the abdominal aorta. In the absence of any signs of atherosclerotic disease, an inflammatory aetiology was suspected, a view that was supported by the macroscopic intraoperative findings and preoperative autoimmune assays. The literature on this rare pathology is examined.

Successful vascular reconstruction after inadvertent femoral artery "stripping"

A case of total stripping of the femoral axis secondary to saphenectomy is reported. This type of accident is followed by amputation unless quickly recognised and corrected. A combined saphenous vein and PTFE graft interposed between the origin of the superficial femoral and the distal part of the posterior tibial remained patent for three months. Its eventual thrombosis, however, did not result in loss of the limb, because a sound compensatory circulation had been established in the meanwhile. It is therefore felt that repair surgery is always worth attempting, even in the case of extensive arterial lesions that will otherwise necessitate amputation.