73 research outputs found
Author response
No full textThe synaptonemal complex (SC) is a polymer that spans ~100 nm between paired homologous chromosomes during meiosis. Its striated, periodic appearance in electron micrographs led to the idea that transverse filaments within this structure 'crosslink' the axes of homologous chromosomes, stabilizing their pairing. SC proteins can also form polycomplexes, three-dimensional lattices that recapitulate the periodic structure of SCs but do not associate with chromosomes. Here we provide evidence that SCs and polycomplexes contain mobile subunits and that their assembly is promoted by weak hydrophobic interactions, indicative of a liquid crystalline phase. We further show that in the absence of recombination intermediates, polycomplexes recapitulate the dynamic localization of pro-crossover factors during meiotic progression, revealing how the SC might act as a conduit to regulate chromosome-wide crossover distribution. Properties unique to liquid crystals likely enable long-range signal transduction along meiotic chromosomes and underlie the rapid evolution of SC proteins
Rubus raduloides (ROG.) SUDRE, eine bislang verkannte Art des europäischen Kontinents
No full textRubus raduloides (ROG.) SUDRE, eine bislang nur von England, Wales und Schottland bekannte Brombeerart, ist ebenso auf dem Kontinent (in den Niederlanden, Belgien und in der Bundesrepublik Deutschland) weit verbreitet, doch hier bisher verkannt und mit anderen Arten verwechselt. Nomenklatorische Fragen, die Verbreitung und Ökologie werden behandelt, und darüber hinaus wird eine detaillierte Beschreibung mit Abbildungen dieser auch in Großbritannien oft falsch interpretierten Art gegeben, um weitere Fehldeutungen zukünftig zu verhindern.Rubus raduloides (ROG.) SUDRE, up to now only known from England, Scotland and Wales is also a wide spread bramble on the continent (The Netherlands, Belgium, Western Germany), but hitherto confused here with other species. Some nomenclaturical problems, the distribution and ecology are discussed and a full description and figures of this also in Britain formerly often misinterpreted species are given in order to prevent false determinations in future. - The author is greatly indebted to the British batologists. E. S. EDEES (Newcastle, Staffordshire) and A. NEWTON (Haie, Cheshire) for their advices and contributions
Building the synaptonemal complex: Molecular interactions between the axis and the central region.
No full textThe successful delivery of genetic material to gametes requires tightly regulated interactions between the parental chromosomes. Central to this regulation is a conserved chromosomal interface called the synaptonemal complex (SC), which brings the parental chromosomes in close proximity along their length. While many of its components are known, the interfaces that mediate the assembly of the SC remain a mystery. Here, we survey findings from different model systems while focusing on insight gained in the nematode C. elegans. We synthesize our current understanding of the structure, dynamics, and biophysical properties of the SC and propose mechanisms for SC assembly
Direct Visualization Reveals Kinetics of Meiotic Chromosome Synapsis
No full textSummaryThe synaptonemal complex (SC) is a conserved protein complex that stabilizes interactions along homologous chromosomes (homologs) during meiosis. The SC regulates genetic exchanges between homologs, thereby enabling reductional division and the production of haploid gametes. Here, we directly observe SC assembly (synapsis) by optimizing methods for long-term fluorescence recording in C. elegans. We report that synapsis initiates independently on each chromosome pair at or near pairing centers—specialized regions required for homolog associations. Once initiated, the SC extends rapidly and mostly irreversibly to chromosome ends. Quantitation of SC initiation frequencies and extension rates reveals that initiation is a rate-limiting step in homolog interactions. Eliminating the dynein-driven chromosome movements that accompany synapsis severely retards SC extension, revealing a new role for these conserved motions. This work provides the first opportunity to directly observe and quantify key aspects of meiotic chromosome interactions and will enable future in vivo analysis of germline processes
Manage and control of the complete production process of IHC Vremac by applying QRM
No full textThis thesis describes an investigation at IHC Vremac, with the goal to improve the delivery performance, from 69% to 85%, focused on how IHC Vremac should manage and control their complete production process when applying Quick Response Manufacturing (QRM). First, the core concepts of QRM were investigated. If a company wants to apply QRM, they have to change the performance measure from delivery performance to MCT reduction (manufacturing critical path time). The company needs to switch from a functional to a cellular organization and needs to improve the flow by reduction of the variability in job arrivals and by increasing the spare capacity to a minimum of 15%. IHC Vremac plans against infinite capacity. There are four releasing points at the office and there is waiting and safety time planned for the production. This leads to 17.5 times more work in progress than necessary. There is a functional separation of machining, welding and assembly. The routings of the orders along the work centers were very diversified. In the future state, the process times and routings must be standardized. The performance measure should change from delivery performance to MCT reduction. There has to be a new strict schedule that is planned with less safety and waiting time and with a minimum spare capacity of 15%, where re-planning should be taken into account. Two QROCs (quick response office cells) need to be created and three QRCs (quick response cells). A priority buffer should be used as work load management. It is recommended to reduce the variability of the job arrivals and to investigate investment in extra machines. Last, there has to be a feedback loop to keep a continuous improvement of the accuracy of process times (CPIs) and routings
SC structure in <i>C</i>. <i>elegans</i>.
No full textTop: Electron micrograph of meiotic chromosomes in C. elegans (adapted from [12]). The electron-dense mass to the sides of the SC is chromatin. Axes (salmon) organize each of the parental chromosomes into an elongated structure by stacking the bases of chromatin loops (blue). The CR (green) assembles between the parallel axes of the homologs. Bottom: Magnified views of the CR and the axis. The CR (left) is composed of SYP-1 through SYP-6. The axis (right) is composed of ring-shaped cohesins (mauve) and the HORMA-domain proteins HTP-3 (orange), which, in turn, recruits the HORMA-domain proteins HIM-3 and HTP-1 and HTP-2 (pink). See Table 1 for more details.</p
The synaptonemal complex has liquid crystalline properties and spatially regulates meiotic recombination factors
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