C1584 in von Willebrand factor is necessary for enhanced proteolysis by ADAMTS13 in vitro

The cysteine variant of the amino acid change tyrosine/cysteine 1584 (Y/C1584) in von Willebrand factor (VWF) has previously been shown to cosegregate with increased susceptibility of VWF to proteolysis by ADAMTS13. It is not known whether C1584 itself confers increased proteolysis or is linked to a causative change elsewhere in VWF. To address whether C1584 underlies enhanced susceptibility of VWF to ADAMTS13-mediated proteolysis, a single family comprising two heterozygous Y/C1584 individuals and four homozygous Y/Y1584 individuals was investigated. The essential regions of the VWF gene were sequenced in all six individuals and ADAMTS13-mediated proteolysis of plasma VWF was assessed for each individual. Comparison of the VWF coding sequences for the Y/C1584 individuals with those for the Y/Y1584 individuals revealed that two amino acid variants were unique to the heterozygotes: R484 and C1584. The plasma VWF of the two heterozygotes showed increased susceptibility to proteolysis in vitro compared with that of the four homozygotes. In the present study we demonstrate that R484, in the absence of C1584, does not influence VWF proteolysis. Enhanced proteolysis occurred only in the presence of Cys1584. Thus, Cys1584 is necessary for increased susceptibility of VWF to proteolysis by ADAMTS13.

Spo11 and the Formation of DNA Double-Strand Breaks in Meiosis

Meiotic recombination is carried out through a specialized pathway for the formation and repair of DNA double-strand breaks made by the Spo11 protein, a relative of archaeal topoisomerase VI. This review summarizes recent studies that provide insight to the mechanism of DNA cleavage by Spo11, functional interactions of Spo11 with other proteins required for break formation, mechanisms that control the timing of recombination initiation, and evolutionary conservation and divergence of these processes.

Meiotic crossover hotspots contained in haplotype block boundaries of the mouse genome

Fertility requires successful chromosome segregation in meiosis, which in most sexual organisms depends on the formation of appropriately placed crossovers. The nonrandom genome-wide distributions of meiotic recombination events have been examined at the molecular level experimentally in yeast and by inference from linkage disequilibrium patterns in humans. Thus far, no method has existed for pinpointing sites of crossing-over on a genome-wide scale in an experimentally tractable animal whose genome size and complexity models that of humans. Here, we present a genomic approach to identify mouse crossover hotspots, based on targeting haplotype block boundaries. This represents a previously undescribed method potentially applicable to large-scale mouse hotspot identification. Using this method, we have successfully predicted the location of two previously uncharacterized crossover hotspots in male mice. As increasing amounts of single-nucleotide polymorphism data emerge, this approach will be useful for investigating the recombination landscape of the mouse genome.

Clinical supervision for mental health nurses in Northern Ireland: formulating best practice guidelines

Nurses work in a constantly challenging and changing environment. Within this context, there is a continuing need for support. Such support will help increase morale, decrease strain and burnout, and encourage self-awareness and self-expression. Clinical supervision address all these issues and enhances the quality of care for patients. While clinical supervision is a policy imperative in Northern Ireland, it was clear that there were problems in its implementation in mental health nursing. The aim of this project was to explore ways to make clinical supervision available to all mental health nurses and to improve and evaluate their contribution to patient care. The research team undertook a comprehensive literature review and a baseline survey of relevant stakeholders. Results represent the outcome of the group work. They will assist healthcare providers to develop local policies and procedures on clinical supervision for practising mental health nurses.

Interactions between Mei4, Rec114, and other proteins required for meiotic DNA double-strand break formation in Saccharomyces cerevisiae

In most sexually reproducing organisms, meiotic recombination is initiated by DNA double-strand breaks (DSBs) formed by the Spo11 protein. In budding yeast, nine other proteins are also required for DSB formation, but the roles of these proteins and the interactions among them are poorly understood. We report further studies of the behaviors of these proteins. Consistent with other studies, we find that Mei4 and Rec114 bind to chromosomes from leptonema through early pachynema. Both proteins showed only limited colocalization with the meiotic cohesin subunit Rec8, suggesting that Mei4 and Rec114 associated preferentially with chromatin loops. Rec114 localization was independent of other DSB factors, but Mei4 localization was strongly dependent on Rec114 and Mer2. Systematic deletion analysis identified protein regions important for a previously described two-hybrid interaction between Mei4 and Rec114. We also report functional characterization of a previously misannotated 5' coding exon of REC102. Sequences encoded in this exon are essential for DSB formation and for Rec102 interaction with Rec104, Spo11, Rec114, and Mei4. Finally, we also examined genetic requirements for a set of previously described two-hybrid interactions that can be detected only when the reporter strain is induced to enter meiosis. This analysis reveals new functional dependencies for interactions among the DSB proteins. Taken together, these studies support the view that Mei4, Rec114, and Mer2 make up a functional subgroup that is distinct from other subgroups of the DSB proteins: Spo11-Ski8, Rec102-Rec104, and Mre11-Rad50-Xrs2. These studies also suggest that an essential function of Rec102 and Rec104 is to connect Mei4 and Rec114 to Spo11.

Epidemiology of adenocarcinoma of the esophagogastric junction

The incidence of adenocarcinoma of the esophagogastric junction has increased rapidly in the later half of the twentieth century in the United States and most western countries. Although squamous cell carcinoma of the esophagus used to predominate, adenocarcinoma of the distal esophagus and esophagogastric junction now accounts for more than half of new diagnoses in western countries. There also has been a shift from the development of distal gastric cancers to ones in a more proximal location. These recent epidemiologic shifts have led to controversy regarding the etiology and treatment of adenocarcinoma of the esophagogastric junction. Uncertainty still exists with regards to nomenclature and classification, risk factors, treatment, and screening and surveillance of esophagogastric adenocarcinoma. This article examines the epidemiology and etiologies of adenocarcinoma of the esophagogastric junction.

Crossover homeostasis in yeast meiosis

Crossovers produced by homologous recombination promote accurate chromosome segregation in meiosis and are controlled such that at least one forms per chromosome pair and multiple crossovers are widely spaced. Recombination initiates with an excess number of double-strand breaks made by Spo11 protein. Thus, crossover control involves a decision by which some breaks give crossovers while others follow a predominantly noncrossover pathway(s). To understand this decision, we examined recombination when breaks are reduced in yeast spo11 hypomorphs. We find that crossover levels tend to be maintained at the expense of noncrossovers and that genomic loci differ in expression of this "crossover homeostasis." These findings define a previously unsuspected manifestation of crossover control, i.e., that the crossover/noncrossover ratio can change to maintain crossovers. Our results distinguish between existing models of crossover control and support the hypothesis that an obligate crossover is a genetically programmed event tied to crossover interference.

Cyclin-dependent kinase directly regulates initiation of meiotic recombination

Meiosis is a specialized cell division that halves the genome complement, producing haploid gametes/spores from diploid cells. Proper separation of homologous chromosomes at the first meiotic division requires the production of physical connections (chiasmata) between homologs through recombinational exchange of chromosome arms after sister-chromatid cohesion is established but before chromosome segregation takes place. The events of meiotic prophase must thus occur in a strictly temporal order, but the molecular controls coordinating these events have not been well elucidated. Here, we demonstrate that the budding yeast cyclin-dependent kinase Cdc28 directly regulates the formation of the DNA double-strand breaks that initiate recombination by phosphorylating the Mer2/Rec107 protein and thereby modulating interactions of Mer2 with other proteins required for break formation. We propose that this function of Cdc28 helps to coordinate the events of meiotic prophase with each other and with progression through prophase.

Clarifying the mechanics of DNA strand exchange in meiotic recombination

During meiosis, accurate separation of maternal and paternal chromosomes requires that they first be connected to one another through homologous recombination. Meiotic recombination has many intriguing but poorly understood features that distinguish it from recombination in mitotically dividing cells, and several of these features depend on the meiosis-specific DNA strand exchange protein Dmc1 (disrupted meiotic cDNA1). Many questions about this protein have arisen since its discovery more than a decade ago, but recent genetic and biochemical breakthroughs promise to shed light on the unique behaviours and functions of this central player in the remarkable chromosome dynamics of meiosis.

Mutations that affect meiosis in male mice influence the dynamics of the mid-preleptotene and bouquet stages

Meiosis pairs and segregates homologous chromosomes and thereby forms haploid germ cells to compensate the genome doubling at fertilization. Homologue pairing in many eukaryotic species depends on formation of DNA double strand breaks (DSBs) during early prophase I when telomeres begin to cluster at the nuclear periphery (bouquet stage). By fluorescence in situ hybridization criteria, we observe that mid-preleptotene and bouquet stage frequencies are altered in male mice deficient for proteins required for recombination, ubiquitin conjugation and telomere length control. The generally low frequencies of mid-preleptotene spermatocytes were significantly increased in male mice lacking recombination proteins SPO11, MEI1, MLH1, KU80, ubiquitin conjugating enzyme HR6B, and in mice with only one copy of the telomere length regulator Terf1. The bouquet stage was significantly enriched in Atm(-/-), Spo11(-/-), Mei1(m1Jcs/m1Jcs), Mlh1(-/-), Terf1(+/-) and Hr6b(-/-) spermatogenesis, but not in mice lacking recombination proteins DMC1 and HOP2, the non-homologous end-joining DNA repair factor KU80 and the ATM downstream effector GADD45a. Mice defective in spermiogenesis (Tnp1(-/-), Gmcl1(-/-), Asm(-/-)) showed wild-type mid-preleptotene and bouquet frequencies. A low frequency of bouquet spermatocytes in Spo11(-/-)Atm(-/-) spermatogenesis suggests that DSBs contribute to the Atm(-/-)-correlated bouquet stage exit defect. Insignificant changes of bouquet frequencies in mice with defects in early stages of DSB repair (Dmc1(-/-), Hop2(-/-)) suggest that there is an ATM-specific influence on bouquet stage duration. Altogether, it appears that several pathways influence telomere dynamics in mammalian meiosis.

Initiation of meiotic recombination by formation of DNA double-strand breaks: mechanism and regulation

Homologous recombination is essential for accurate chromosome segregation during meiosis in most sexual organisms. Meiotic recombination is initiated by the formation of DSBs (DNA double-strand breaks) made by the Spo11 protein. We review here recent findings pertaining to protein–protein interactions important for DSB formation, the mechanism of an early step in the processing of Spo11-generated DSBs, and regulation of DSB formation by protein kinases.

Synaptonemal complex formation: where does it start?

The synaptonemal complex is a prominent, evolutionarily conserved feature of meiotic prophase. The assembly of this structure is closely linked to meiotic recombination. A recent study in budding yeast reveals an unexpected role in centromere pairing for a protein component of the synaptonemal complex, Zip1. These findings have implications for synaptonemal complex formation.

Surveillance of different recombination defects in mouse spermatocytes yields distinct responses despite elimination at an identical developmental stage

Fundamentally different recombination defects cause apoptosis of mouse spermatocytes at the same stage in development, stage IV of the seminiferous epithelium cycle, equivalent to mid-pachynema in normal males. To understand the cellular response(s) that triggers apoptosis, we examined markers of spermatocyte development in mice with different recombination defects. In Spo11(-)(/)(-) mutants, which lack the double-strand breaks (DSBs) that initiate recombination, spermatocytes express markers of early to mid-pachynema, forming chromatin domains that contain sex body-associated proteins but that rarely encompass the sex chromosomes. Dmc1(-)(/)(-) spermatocytes, impaired in DSB repair, appear to arrest at or about late zygonema. Epistasis analysis reveals that this earlier arrest is a response to unrepaired DSBs, and cytological analysis implicates the BRCT-containing checkpoint protein TOPBP1. Atm(-)(/)(-) spermatocytes show similarities to Dmc1(-)(/)(-) spermatocytes, suggesting that ATM promotes meiotic DSB repair. Msh5(-)(/)(-) mutants display a set of characteristics distinct from these other mutants. Thus, despite equivalent stages of spermatocyte elimination, different recombination-defective mutants manifest distinct responses, providing insight into surveillance mechanisms in male meiosis.

Endonucleolytic processing of covalent protein-linked DNA double-strand breaks

DNA double-strand breaks (DSBs) with protein covalently attached to 5' strand termini are formed by Spo11 to initiate meiotic recombination. The Spo11 protein must be removed for the DSB to be repaired, but the mechanism for removal is unclear. Here we show that meiotic DSBs in budding yeast are processed by endonucleolytic cleavage that releases Spo11 attached to an oligonucleotide with a free 3'-OH. Two discrete Spo11-oligonucleotide complexes were found in equal amounts, differing with respect to the length of the bound DNA. We propose that these forms arise from different spacings of strand cleavages flanking the DSB, with every DSB processed asymmetrically. Thus, the ends of a single DSB may be biochemically distinct at or before the initial processing step-much earlier than previously thought. SPO11-oligonucleotide complexes were identified in extracts of mouse testis, indicating that this mechanism is evolutionarily conserved. Oligonucleotide-topoisomerase II complexes were also present in extracts of vegetative yeast, although not subject to the same genetic control as for generating Spo11-oligonucleotide complexes. Our findings suggest a general mechanism for repair of protein-linked DSBs.

The molecular analysis of haemophilia A: a guideline from the UK haemophilia centre doctors' organization haemophilia genetics laboratory network

Haemophilia A is a common inherited bleeding disorder that has a well-understood pathophysiology. Our understanding of the molecular genetics of the disease has allowed the development of comprehensive carrier and prenatal diagnosis for this single gene defect. Continuing technological developments improve our ability to provide genetic analysis in a rapid and cost effective manner. This guideline aims to provide advice on current best laboratory practice when approaching genetic diagnosis of haemophilia A.

The molecular analysis of haemophilia B: a guideline from the UK haemophilia centre doctors' organization haemophilia genetics laboratory network

Haemophilia B is one of the most common inherited bleeding disorders and has a well understood pathophysiology. Our understanding of the molecular genetics of the disease has allowed the development of comprehensive carrier and prenatal diagnosis for this single gene disorder. Continuing technological developments improve our ability to provide genetic analysis in a rapid and cost-effective manner. This guideline aims to provide advice on current best laboratory practice when approaching genetic diagnosis of haemophilia B.

Homologous recombination: needing to have my say

Recent studies in budding and fission yeasts have revealed Mei5 and Sae3 as factors necessary for the proper function of the recombinases Dmc1 and Rad51 in DNA repair and meiotic recombination, providing new insights into how strand exchange proteins are directed along specific recombination pathways.

H2B (Ser10) Phosphorylation is Induced during Apoptosis and Meiosis in S. cerevisiae

The nucleosome, composed of an octamer of highly conserved histone proteins and associated DNA, is the fundamental unit of eukaryotic chromatin. How arrays of nucleosomes are folded into higher-order structures, and how the dynamics of such compaction are regulated, are questions that remain largely unanswered. Our recent studies demonstrated that phosphorylation of histone H2B is necessary to induce cell death that exhibits phenotypic hallmarks of apoptosis including DNA fragmentation and chromatin condensation in yeast (serine 10)1 and in mammalian cells (serine 14)2. In this article, we extend these findings by uncovering a role for H2B phosphorylation at serine 10 (Ser10) in another biological event that is associated with dramatic alterations in higher-order chromatin structure, meiosis. Our data show strong staining, indicative of H2B (Ser10) phosphorylation, during the pachytene stage of yeast meiotic prophase. These data broaden the use of this phosphorylation mark in chromatin remodeling that closely correlates with chromatin compaction. How phosphorylation marks are translated into meaningful downstream events during processes as diverse as apoptosis and meiosis remain a challenge for future studies.

Distinct DNA-damage-dependent and -independent responses drive the loss of oocytes in recombination-defective mouse mutants

Defects in meiotic recombination in many organisms result in arrest because of activation of a meiotic checkpoint(s). The proximal defect that triggers this checkpoint in mammalian germ cells is not understood, but it has been suggested to involve either the presence of DNA damage in the form of unrepaired recombination intermediates or defects in homologous chromosome pairing and synapsis independent of DNA damage per se. To distinguish between these possibilities in the female germ line, we compared mouse oocyte development in a mutant that fails to form the double-strand breaks (DSBs) that initiate meiotic recombination (Spo11-/-) to mutants with defects in processing DSBs when they are formed (Dmc1-/- and Msh5-/-), and we examined the epistasis relationships between these mutations. Absence of DSB formation caused a partial defect in follicle formation, whereas defects in DSB repair caused earlier and more severe meiotic arrest, which could be suppressed by eliminating DSB formation. Therefore, our analysis reveals that there are both DNA-damage-dependent and -independent responses to recombination errors in mammalian oocytes. By using these findings as a paradigm, we also examined oocyte loss in mutants lacking the DNA-damage checkpoint kinase ATM. The absence of ATM caused defects in folliculogenesis that were similar to those in Dmc1 mutants and that could be suppressed by Spo11 mutation, implying that oocyte death in Atm-deficient animals is a response to defective DSB repair.

Modifying histones and initiating meiotic recombination; new answers to an old question

It is well documented that the formation of the DNA double-strand breaks (DSBs) that initiate meiotic recombination is influenced by chromatin and larger scale chromosome organization, but the molecular nature of this influence has remained elusive. Several recent studies, including (this issue of Cell), shed light on this issue by revealing roles for posttranslational histone modifications in promoting DSB formation.

A common ancestral mutation (C128X) occurring in 11 non-Jewish families from the UK with factor XI deficiency

Factor XI (FXI) deficiency is a mild bleeding disorder that is particularly common in Ashkenazi Jews, but has been reported in all populations. In Jews, two FXI gene (F11) mutations (a stop codon in exon 5, E117X, type II, and a point mutation in exon 9, F283L, type III) are particularly common, but in other populations a variety of different mutations have been described. In the Basque region of France one mutation, C38R in exon 3, was found in eight of 12 families studied, haplotype analysis suggesting a founder effect. In the course of screening 78 unrelated individuals (including 15 Jewish and 12 Asian) we have found 10 Caucasian non-Jewish patients with the mutation C128X in exon 5. Individuals were investigated because of a personal or family history of bleeding, or finding a prolonged activated partial thromboplastin time. Individuals negative for the type II and type III mutations were screened by a combination of SSCP and heteroduplex analysis. The C128X mutation was found in 10 families (one previously described). Among three individuals with severe FXI deficiency, one was homozygous for the C128X mutation, and two were compound heterozygotes for the C128X and another mutation; other individuals were carriers of the C128X mutation. This is a nonsense mutation producing a truncated protein; individuals have FXI antigen levels concordant with FXI coagulant activity. Haplotype analysis of 11 families, including a further kindred previously reported from the USA, but which originally came from the UK (in which the index patient was homozygous for C128X), suggests a founder effect.

Antiviral protein Ski8 is a direct partner of Spo11 in meiotic DNA break formation, independent of its cytoplasmic role in RNA metabolism

Meiotic recombination initiates with double-strand breaks (DSBs) catalyzed by Spo11 in conjunction with accessory proteins whose roles are not understood. Two-hybrid analysis reveals a network of interactions connecting the yeast DSB proteins to one another. Of these proteins, Ski8 was known to function in cytoplasmic RNA metabolism, suggesting that its role in recombination might be indirect. However, obligate partners of Ski8 in RNA metabolism are dispensable for recombination and Ski8 relocalizes to the nucleus and associates with chromosomes specifically during meiosis. Interaction of Ski8 with Spo11 is essential for DSB formation and Ski8 relocalization. Thus, Ski8 plays distinct roles in RNA metabolism and, as a direct partner of Spo11, in DSB formation. Ski8 works with Spo11 to recruit other DSB proteins to meiotic chromosomes, implicating Ski8 as a scaffold protein mediating assembly of a multiprotein complex essential for DSB formation.