223 research outputs found
Increased accuracy of ligand sensing by receptor internalization
Many types of cells can sense external ligand concentrations with
cell-surface receptors at extremely high accuracy. Interestingly, ligand-bound
receptors are often internalized, a process also known as receptor-mediated
endocytosis. While internalization is involved in a vast number of important
functions for the life of a cell, it was recently also suggested to increase
the accuracy of sensing ligand as the overcounting of the same ligand molecules
is reduced. Here we show, by extending simple ligand-receptor models to
out-of-equilibrium thermodynamics, that internalization increases the accuracy
with which cells can measure ligand concentrations in the external environment.
Comparison with experimental rates of real receptors demonstrates that our
model has indeed biological significance.Comment: 9 pages, 4 figures, accepted for publication in Physical Review
Understanding Minnesota's Q Comp Program
Capstone paper for the fulfillment of the Master of Public Policy degree.Minnesotaβs Quality Compensation program (Q Comp) is a unique initiative that seeks to provide districts with the tools to better support teachers in developing their professional practice. The program requires participants to utilize four specific components while still allowing wide flexibility in local design and implementation. Districts and charter schools seeking to adopt or amend Q Comp plans can learn from both the existing body of research and other districtsβ experiences with implementation. This paper includes a literature review of each component individually, a summary of existing research about Q Comp specifically, and a synthesis of common themes from interviews with various school staff, union representatives and other local experts around the Twin Cities metro. Using that knowledge and an assessment of the current political landscape in the state, we conclude with five recommendations for districts. These recommendations apply to any district or charter school planning to adopt or amend a Q Comp plan. We recommend that districts or charter schools:
β Start the process by getting on the waiting list now.
β Teachers take the lead in writing the plan.
β Think about needs and professional development locally.
β Use opportunities for innovation, but also integrate into existing strategy.
β Be responsive and flexible about implementation
end3 and end4: two mutants defective in receptor-mediated and fluid-phase endocytosis in Saccharomyces cerevisiae.
Putting theory oriented evaluation into practice
Evaluations of gaming simulations and business games as teaching devices are typically end-state driven. This emphasis fails to detect how the simulation being evaluated does or does not bring about its desired consequences. This paper advances the use of a logic model approach which possesses a holistic perspective that aims at including all elements associated with the situation created by a game. The use of the logic model approach is illustrated as applied to Simgame, a board game created for secondary school level business education in six European Union countries
The initial education of high school teachers : a critical review of major issues and trends
This paper draws on major research findings in international literature in order to provide a critical
review of a number of key issues and trends in the initial education of high school teachers. Firstly,
this paper contextualizes the prevalent discourse surrounding the field of initial teacher education
(ITE) and explores the effect that this discourse has on the conceptualization of teachersβ work.
Secondly, this paper focuses on the debates regarding the most propitious site for the teacher
education enterprise, the programme structure for ITE, the field placement or practicum, the
relationship between subject study and pedagogy, and the overall effectiveness of teacher education.
The paper concludes by considering the new challenges that the field of initial teacher education
must confront and the implications of such challenges for the ITE curriculum.peer-reviewe
Learning based on library automation in mobile devices: The video production by students of Universidade Federal do Cariri Library Science Undergraduate Degree
An Abp1-Dependent Route of Endocytosis Functions when the Classical Endocytic Pathway in Yeast Is Inhibited
Clathrin-mediated endocytosis (CME) is a well characterized pathway in both yeast and mammalian cells. An increasing number of alternative endocytic pathways have now been described in mammalian cells that can be both clathrin, actin, and Arf6- dependent or independent. In yeast, a single clathrin-mediated pathway has been characterized in detail. However, disruption of this pathway in many mutant strains indicates that other uptake pathways might exist, at least for bulk lipid and fluid internalization. Using a combination of genetics and live cell imaging, here we show evidence for a novel endocytic pathway in S. cerevisiae that does not involve several of the proteins previously shown to be associated with the βclassicβ pathway of endocytosis. This alternative pathway functions in the presence of low levels of the actin-disrupting drug latrunculin-A which inhibits movement of the proteins Sla1, Sla2, and Sac6, and is independent of dynamin function. We reveal that in the absence of the βclassicβ pathway, the actin binding protein Abp1 is now essential for bulk endocytosis. This novel pathway appears to be distinct from another described alternative endocytic route in S. cerevisiae as it involves at least some proteins known to be associated with cortical actin patches rather than being mediated at formin-dependent endocytic sites. These data indicate that cells have the capacity to use overlapping sets of components to facilitate endocytosis under a range of conditions
Interaction of the Deubiquitinating Enzyme Ubp2 and the E3 Ligase Rsp5 Is Required for Transporter/Receptor Sorting in the Multivesicular Body Pathway
Protein ubiquitination is essential for many events linked to intracellular protein trafficking. We sought to elucidate the possible involvement of the S. cerevisiae deubiquitinating enzyme Ubp2 in transporter and receptor trafficking after we (this study) and others established that affinity purified Ubp2 interacts stably with the E3 ubiquitin ligase Rsp5 and the (ubiquitin associated) UBA domain containing protein Rup1. UBP2 interacts genetically with RSP5, while Rup1 facilitates the tethering of Ubp2 to Rsp5 via a PPPSY motif. Using the uracil permease Fur4 as a model reporter system, we establish a role for Ubp2 in membrane protein turnover. Similar to hypomorphic rsp5 alleles, cells deleted for UBP2 exhibited a temporal stabilization of Fur4 at the plasma membrane, indicative of perturbed protein trafficking. This defect was ubiquitin dependent, as a Fur4 N-terminal ubiquitin fusion construct bypassed the block and restored sorting in the mutant. Moreover, the defect was absent in conditions where recycling was absent, implicating Ubp2 in sorting at the multivesicular body. Taken together, our data suggest a previously overlooked role for Ubp2 as a positive regulator of Rsp5-mediated membrane protein trafficking subsequent to endocytosis
Regulation of Alr1 Mg Transporter Activity by Intracellular Magnesium
Mg homeostasis is critical to eukaryotic cells, but the contribution of Mg transporter activity to homeostasis is not fully understood. In yeast, Mg uptake is primarily mediated by the Alr1 transporter, which also allows low affinity uptake of other divalent cations such as Ni2+, Mn2+, Zn2+ and Co2+. Using Ni2+ uptake to assay Alr1 activity, we observed approximately nine-fold more activity under Mg-deficient conditions. The mnr2 mutation, which is thought to block release of vacuolar Mg stores, was associated with increased Alr1 activity, suggesting Alr1 was regulated by intracellular Mg supply. Consistent with a previous report of the regulation of Alr1 expression by Mg supply, Mg deficiency and the mnr2 mutation both increased the accumulation of a carboxy-terminal epitope-tagged version of the Alr1 protein (Alr1-HA). However, Mg supply had little effect on ALR1 promoter activity or mRNA levels. In addition, while Mg deficiency caused a seven-fold increase in Alr1-HA accumulation, the N-terminally tagged and untagged Alr1 proteins increased less than two-fold. These observations argue that the Mg-dependent accumulation of the C-terminal epitope-tagged protein was primarily an artifact of its modification. Plasma membrane localization of YFP-tagged Alr1 was also unaffected by Mg supply, indicating that a change in Alr1 location did not explain the increased activity we observed. We conclude that variation in Alr1 protein accumulation or location does not make a substantial contribution to its regulation by Mg supply, suggesting Alr1 activity is directly regulated via as yet unknown mechanisms
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