In meiosis I, homologous chromosomes segregate away from each other-the first of two rounds of chromosome segregation that allow the formation of haploid gametes. In prophase I, homologous partners ...become joined along their length by the synaptonemal complex (SC) and crossovers form between the homologs to generate links called chiasmata. The chiasmata allow the homologs to act as a single unit, called a bivalent, as the chromosomes attach to the microtubules that will ultimately pull them away from each other at anaphase I. Recent studies, in several organisms, have shown that when the SC disassembles at the end of prophase, residual SC proteins remain at the homologous centromeres providing an additional link between the homologs. In budding yeast, this centromere pairing is correlated with improved segregation of the paired partners in anaphase. However, the causal relationship of prophase centromere pairing and subsequent disjunction in anaphase has been difficult to demonstrate as has been the relationship between SC assembly and the assembly of the centromere pairing apparatus. Here, a series of in-frame deletion mutants of the SC component Zip1 were used to address these questions. The identification of a separation-of-function allele that disrupts centromere pairing, but not SC assembly, has made it possible to demonstrate that centromere pairing and SC assembly have mechanistically distinct features and that the centromere pairing function of Zip1 drives disjunction of the paired partners in anaphase I.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In meiosis, homologous chromosomes face the obstacle of finding, holding onto and segregating away from their partner chromosome. There is increasing evidence, in a diverse range of organisms, that ...centromere–centromere interactions that occur in late prophase are an important mechanism in ensuring segregation fidelity. Centromere pairing appears to initiate when homologous chromosomes synapse in meiotic prophase. Structural proteins of the synaptonemal complex have been shown to help mediate centromere pairing, but how the structure that maintains centromere pairing differs from the structure of the synaptonemal complex along the chromosomal arms remains unknown. When the synaptonemal complex proteins disassemble from the chromosome arms in late prophase, some of these synaptonemal complex components persist at the centromeres. In yeast and Drosophila these centromere‐pairing behaviors promote the proper segregation of chromosome partners that have failed to become linked by chiasmata. Recent studies of mouse spermatocytes have described centromere pairing behaviors that are similar in several respects to what has been described in the fly and yeast systems. In humans, chromosomes that fail to experience crossovers in meiosis are error‐prone and are a major source of aneuploidy. The finding that centromere pairing is a conserved phenomenon raises the possibility that it may play a role in promoting the segregation fidelity of non‐exchange chromosome pairs in humans.
In meiosis I, chromosomes become paired with their homologous partners and then are pulled toward opposite poles of the spindle. In the budding yeast, Saccharomyces cerevisiae, in early meiotic ...prophase, centromeres are observed to associate in pairs in a homology-independent manner; a process called centromere coupling. Later, as homologous chromosomes align, their centromeres associate in a process called centromere pairing. The synaptonemal complex protein Zip1 is necessary for both types of centromere association. We aimed to test the role of centromere coupling in modulating recombination at centromeres, and to test whether the two types of centromere associations depend upon the same sets of genes. The zip1-S75E mutation, which blocks centromere coupling but no other known functions of Zip1, was used to show that in the absence of centromere coupling, centromere-proximal recombination was unchanged. Further, this mutation did not diminish centromere pairing, demonstrating that these two processes have different genetic requirements. In addition, we tested other synaptonemal complex components, Ecm11 and Zip4, for their contributions to centromere pairing. ECM11 was dispensable for centromere pairing and segregation of achiasmate partner chromosomes; while ZIP4 was not required for centromere pairing during pachytene, but was required for proper segregation of achiasmate chromosomes. These findings help differentiate the two mechanisms that allow centromeres to interact in meiotic prophase, and illustrate that centromere pairing, which was previously shown to be necessary to ensure disjunction of achiasmate chromosomes, is not sufficient for ensuring their disjunction.
Faithful chromosome segregation during meiosis I depends upon the formation of connections between homologous chromosomes. Crossovers between homologs connect the partners, allowing them to attach to ...the meiotic spindle as a unit, such that they migrate away from one another at anaphase I. Homologous partners also become connected by pairing of their centromeres in meiotic prophase. This centromere pairing can promote proper segregation at anaphase I of partners that have failed to become joined by a crossover. Centromere pairing is mediated by synaptonemal complex (SC) proteins that persist at the centromere when the SC disassembles. Here, using mouse spermatocyte and yeast model systems, we tested the role of shugoshin in promoting meiotic centromere pairing by protecting centromeric synaptonemal components from disassembly. The results show that shugoshin protects the centromeric SC in meiotic prophase and, in anaphase, promotes the proper segregation of partner chromosomes that are not linked by a crossover.
Adoptive T‐cell therapies (ATCTs) are increasingly important for the treatment of cancer, where patient immune cells are engineered to target and eradicate diseased cells. The biomanufacturing of ...ATCTs involves a series of time‐intensive, lab‐scale steps, including isolation, activation, genetic modification, and expansion of a patient's T‐cells prior to achieving a final product. Innovative modular technologies are needed to produce cell therapies at improved scale and enhanced efficacy. In this work, well‐defined, bioinspired soft materials are integrated within flow‐based membrane devices for improving the activation and transduction of T‐cells. Hydrogel coated membranes (HCM) functionalized with cell‐activating antibodies are produced as a tunable biomaterial for the activation of primary human T‐cells. T‐cell activation utilizing HCMs lead to highly proliferative T‐cells that express a memory phenotype. Further, transduction efficiency is improved by several folds over static conditions by using a tangential flow filtration (TFF) flow‐cell, commonly used in the production of protein therapeutics, to transduce T‐cells under flow. The combination of HCMs and TFF technology leads to increased cell activation, proliferation, and transduction compared to current industrial biomanufacturing processes. The combined power of biomaterials with scalable flow‐through transduction techniques provides future opportunities for improving the biomanufacturing of ATCTs.
Well‐defined, bioinspired soft materials are integrated within scalable, flow‐based membrane devices for improving the activation and transduction of T‐cells, which are essential steps in the production of adoptive T‐cell therapies. These innovative technologies provide opportunities for improving the manufacturing of cell therapies.
The segregation of chromosomes during meiosis is complicated by a unique obstacle not shared with mitosis—homologous chromosomes must find one another and form a stable association that persists ...until anaphase I. Throughout meiotic prophase in budding yeast, Saccharomyces cerevisiae, chromosomes interact in a number of ways at the centromere. First, in early prophase, centromeres interact with non-homologous partner centromeres through a phenomenon called centromere coupling. The second type of centromere-centromere interaction typically occurs between homologous chromosome centromeres. This unique and conserved phenomenon, termed centromere pairing, has been found to be important for segregation of chromosomes, especially those that fail to form a crossover (termed achiasmate chromosomes). Both of these centromere-centromere tetherings are mediated by a functionally-conserved structural protein, Zip1. The focus of this work is the examination of the role Zip1 plays in these centromere associations in prophase, and by what mechanism Zip1 is moderated to assume its many different roles, in synchrony with the rest of meiotic progression. To tackle these questions, we implemented the use of many different variations of the ZIP1 gene—including a phosphomimetic mutant incapable of centromere coupling, a series of nine in-frame deletion mutants, and a series of short truncated portions of Zip1 fused to a fluorescent protein. From this work, we have been able to find sufficient evidence to conclude centromere coupling and pairing are distinct mechanisms, controlled by separate processes, both mediated by Zip1. Portions of the N- and C-termini of Zip1 have been identified as critical for centromere coupling, while a different portion of the N-terminus of Zip1 has been identified to be critical for centromere pairing and achiasmate chromosome segregation. In addition, we have begun to shed light on the aspects of the mechanism, distinct from centromere pairing itself, that promotes achiasmate segregation. Zip4 and Shugoshin 1 are two proteins implicated in this mechanism. Possible models for how centromere pairing leads to proper chromosome segregation are discussed.
The relatively low density of weather radar networks can lead to low-altitude coverage gaps. As existing networks are evaluated for gap fillers and new networks are designed, the benefits of ...low-altitude coverage must be assessed quantitatively. This study takes a regression approach to modeling quantitative precipitation estimation (QPE) differences based on network density, antenna aperture, and polarimetric bias. Thousands of cases from the warm-season months of May–August 2015–17 are processed using both the specific attenuation R(A) and reflectivity–differential reflectivity R(Z, Z
DR) QPE methods and are compared with Automated Surface Observing System (ASOS) rain gauge data. QPE errors are quantified on the basis of beam height, cross-radial resolution, added polarimetric bias, and observed rainfall rate. The collected data are used to construct a support vector machine regression model that is applied to the current WSR-88D network for holistic error quantification. An analysis of the effects of polarimetric bias on flash-flood rainfall rates is presented. Rainfall rates that are based on 2-yr/1-h return rates are used for a contiguous-U.S.-wide analysis of QPE errors in extreme rainfall situations. These errors are then requantified using previously proposed network design scenarios with additional radars that provide enhanced estimate capabilities. Last, a gap-filling scenario utilizing the QPE error model, flash-flood rainfall rates, population density, and potential additional WSR-88D sites is presented, exposing the highest-benefit coverage holes in augmenting the WSR-88D network (or a future network) relative to QPE performance.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In 2016, the FAA, NOAA, DoD, and DHS initiated a feasibility study for a Spectrum Efficient National Surveillance Radar (SENSR). The goal is to assess approaches for vacating the 1.3- to 1.35-GHz ...radio frequency band currently allocated to FAA/DoD long-range radars so that this band can be auctioned for commercial use. As part of this goal, the participating agencies have developed preliminary performance requirements that not only assume minimum capabilities based on legacy radars, but also recognize the need for enhancements in future radar networks. The relatively low density of the legacy radar networks, especially the WSR-88D network, had led to the goal of enhancing low-altitude weather coverage. With multiple design metrics and network possibilities still available to the SENSR agencies, the benefits of low-altitude coverage must be assessed quantitatively. This study lays the groundwork for estimating Quantitative Precipitation Estimation (QPE) differences based on network density, array size, and polarimetric bias. These factors create a pareto front of cost-benefit for QPE in a new radar network, and these results will eventually be used to determine appropriate tradeoffs for SENSR requirements. Results of this study are presented in the form of two case examples that quantify errors based on polarimetric bias and elevation, along with a description of eventual application to a national network in upcoming expansion of the work.
PDF
