1,720,964 research outputs found
Regulation of stem cell maintenance and cell differentiation states in Arabidopsis root development
No full textThe experiments presented in this thesis topic the role of transcription factor family members in regulating growth, development, and maintenance of the Arabidopsis root. We demonstrate a conserved homeobox transcription factor regulates distal stem cell maintenance and expand the notion that the PLETHORA (PLT) family of transcription factors specifically regulates stem cell properties to a significantly broader role. In addition, we show that members of the PLT gene family can activate transcriptional targets in a dose-dependent fashion to establish a feed-forward network that regulates root growth and development. Chapter one reviews the molecular genetical approaches that have been adopted to address Arabidopsis root development. Taking embryogenesis as a starting point, we describe the genes and mechanisms involved in root meristem and stem cell patterning and maintenance. In chapter two we demonstrate a role for the homeobox gene WOX5 (WUSCHEL-RELATED 5), a homologue of WUS, in regulating distal stem cell maintenance in a non-cell autonomous fashion downstream from the SHR/SCR signaling pathway. While loss-of-function leads to stem cell differentiation, overexpression of WOX5 results in the accumulation of distal stem cells that operate independent from quiescent centre (QC) signaling. By reciprocal expression experiments we show that WOX5 and WUS are functionally equivalent in stem cell control, indicating that the organizers of both stem cell systems employ related regulators to provide stem cell maintenance signaling. Chapter three describes the functional analysis of four PLT family members that are redundantly required for embryonic root development and post-embryonic root growth in a dose-dependent fashion. Transcriptional and translational studies of the PLT proteins reveal their graded expression spanning the root meristem with highest expression in the stem cell area, intermediate levels in the transit amplifying zone, and low levels in the differentiation zone. By changing the shape of the PLT expression patterns we show that cell fate within the root meristem depends on the amount of PLT cells are subjected to; high PLT levels maintain stem cell fate, intermediate levels control cell division, and low levels allow cell elongation. Chapter four elaborates on the PLT dosage-dependent control of root cell fate by demonstrating that direct targets of PLT2 are expressed in non-overlapping expression domains within the root meristem. By manipulating PLT2 protein levels in the root meristem, we demonstrate a corresponding shift in the target expression domain; indicating PLT2 can regulate its transcriptional targets in a concentration-dependent manner. In addition, the varied identity of downstream targets suggests that PLT2 controls diversified developmental pathways associated with cell proliferation and growth. Interestingly, the identification of auxin transport facilitators, biosynthetic regulators and signaling components as direct PLT2 targets indicate a multi-level regulatory feedback into the auxin gradient that specifies root patterning. In chapter five the results presented in the previous chapters will be discussed in the light of recent insights in stem cell maintenance and specification, morphogen theory and transcriptional networks to give directions to future research
Transcription factor movement and tissue patterning in Arabidopsis root meristem
No full textCell-cell communication is key to coordinated cellular functions in multicellular organisms. In addition to the signaling molecules found in animals, plants also frequently recruit mobile transcription factors to deliver positional information. The best studied example is SHORT-ROOT (SHR), a transcription factor which moves outward from the central vasculature to specify the cell fates of quiescent center (QC), the stem cell cortex/endodermis initial and its daughter (CEI/D) and endodermis in the adjacent cell layer in the root of the model organism Arabidopsis thaliana. SHR is required together with its downstream target SCARECROW (SCR) for the formative divisions of CEI/D and separation of endodermis and cortex. Intensive studies have revealed that SHR intercellular mobility is linked to its subcellular localization, while formative divisions at the CEI/D position is determined by a regulatory network involving SHR and SCR. Despite these advances, additional regulatory mechanisms are needed to fully explain the regulation of SHR movement and action range. SHR movement is regulated by a zinc finger protein JACKDAW (JKD). We described the function of three JKD homologs and members of the “BIRD protein family” – BALDIBIS (BIB), MAGPIE (MGP) and NUTCRACKER (NUC) – and observed that they constrain SHR movement through nuclear retention while fine-tuning transcription of key SHR targets including SCR and CYCLIN D6 (CYCD6). JKD and the studied BIRD proteins promote tissue specifications to continuously stabilize tissue boundaries in the root meristem, highlighting the developmental plasticity in plants. SHR, SCR and the BIRD proteins are largely present in the QC, CEI/D and endodermis, yet different cell types are specified by their interplay. They are also likely to form protein complexes thanks to their inter-binding capacity. We hypothesized that they might form distinct protein complexes in different cells to precisely regulate their behaviors. We optimized the imaging technique Förster resonance energy transfer (FRET) measured by fluorescence lifetime imaging microscopy (FLIM) for Arabidopsis roots, and observed that SHR-SCR interaction is enriched in the CEI/D. We then confirmed that enhanced SHR-SCR interaction correlates with formative divisions, while JKD binds SHR and SCR in spatially complementary manners to repress undesired divisions outside CEI/D. Binding competition assays suggest that SHR, SCR and BIRD proteins are incorporated in higher order protein complexes. Together, these data indicate that differential protein interactions are associated with different cell fate specifications, and suggest how multicellular organisms might employ a limited set of regulatory factors to trigger various developmental processes. JKD can act as a guiding molecule for SHR into specific subnuclear bodies. We generated two JKD mutant variants with opposite effect on SHR regulation: one enhances SHR subnuclear body localization while repressing SCR and CYCD6 expression, the other fails to enrich SHR into subnuclear structures but enhances target transcription. Our data provide evidence of JKD subnuclear compartmentalization as a means to regulate target gene expression. We also described the function of SCARECROW-LIKE23 (SCL23), the closest homolog of SCR in Arabidopsis. SCL23 is also a mobile protein and that it restricts SHR movement without nuclear retention, adding more complexity towards SHR regulation during root development
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Regulation of stem cell maintenance and cell differentiation states in Arabidopsis root development
No full textThe experiments presented in this thesis topic the role of transcription factor family members in regulating growth, development, and maintenance of the Arabidopsis root. We demonstrate a conserved homeobox transcription factor regulates distal stem cell maintenance and expand the notion that the PLETHORA (PLT) family of transcription factors specifically regulates stem cell properties to a significantly broader role. In addition, we show that members of the PLT gene family can activate transcriptional targets in a dose-dependent fashion to establish a feed-forward network that regulates root growth and development. Chapter one reviews the molecular genetical approaches that have been adopted to address Arabidopsis root development. Taking embryogenesis as a starting point, we describe the genes and mechanisms involved in root meristem and stem cell patterning and maintenance. In chapter two we demonstrate a role for the homeobox gene WOX5 (WUSCHEL-RELATED 5), a homologue of WUS, in regulating distal stem cell maintenance in a non-cell autonomous fashion downstream from the SHR/SCR signaling pathway. While loss-of-function leads to stem cell differentiation, overexpression of WOX5 results in the accumulation of distal stem cells that operate independent from quiescent centre (QC) signaling. By reciprocal expression experiments we show that WOX5 and WUS are functionally equivalent in stem cell control, indicating that the organizers of both stem cell systems employ related regulators to provide stem cell maintenance signaling. Chapter three describes the functional analysis of four PLT family members that are redundantly required for embryonic root development and post-embryonic root growth in a dose-dependent fashion. Transcriptional and translational studies of the PLT proteins reveal their graded expression spanning the root meristem with highest expression in the stem cell area, intermediate levels in the transit amplifying zone, and low levels in the differentiation zone. By changing the shape of the PLT expression patterns we show that cell fate within the root meristem depends on the amount of PLT cells are subjected to; high PLT levels maintain stem cell fate, intermediate levels control cell division, and low levels allow cell elongation. Chapter four elaborates on the PLT dosage-dependent control of root cell fate by demonstrating that direct targets of PLT2 are expressed in non-overlapping expression domains within the root meristem. By manipulating PLT2 protein levels in the root meristem, we demonstrate a corresponding shift in the target expression domain; indicating PLT2 can regulate its transcriptional targets in a concentration-dependent manner. In addition, the varied identity of downstream targets suggests that PLT2 controls diversified developmental pathways associated with cell proliferation and growth. Interestingly, the identification of auxin transport facilitators, biosynthetic regulators and signaling components as direct PLT2 targets indicate a multi-level regulatory feedback into the auxin gradient that specifies root patterning. In chapter five the results presented in the previous chapters will be discussed in the light of recent insights in stem cell maintenance and specification, morphogen theory and transcriptional networks to give directions to future research
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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