1,721,022 research outputs found
The role of Sox4 in normal intestine and colorectal cancer
Get PDFThe intestinal epithelium is one of the most rapidly dividing tissues in the
mammalian organism, with near complete replacement of the epithelial monolayer every 7-10
days (Wright et al., 1984). The start site of this impressive cellular renewal and division begins
with a pool of intestinal epithelial stem cells (IESCs) that reside at the base of the crypts. The
crypts are small depressions in the intestine that extend to the lamina propria and house both the
IESCs and supporting niche cells at its base (Cheng et al., 1974). As the IESCs divide, their
progeny migrate upward to the top of the crypt towards the lumen, into what is termed the
transit-amplifying zone. Once in this zone, the transit
amplifying cells mature into one of four well defined postmitotic
cell lineages: absorptive enterocytes, goblet cells,
enteroendocrine cells, and Paneth cells (Figure 1). With the
exception of the Paneth cells, all of these cell types continue
to migrate upward into the large finger-like villi, where they
live for several days before dying and being sloughed off at
the tip of the villus (Cheng et al., 1974). Each cell type in the
villus has a distinct role; absorptive enterocytes are
responsible for absorbing nutrients and transferring them to
the bloodstream, goblet cells secrete a protective mucus layer
over the epithelium, and enteroendocrine cells produce
important signaling hormones (Cheng et al., 1974). Paneth cells are unique in that they migrate
downward from the transit-amplifying zone back to the crypt base where they secrete
antimicrobial peptides and serve as niche cells to the stem cells (Sato et al., 2011). This rapid
cycle of tissue renewal, coupled with well-defined post-mitotic lineages, make the intestinal
epithelium an ideal model for the study of factors that regulate the potency and self renewing
capability of the IESCs, which to date remain poorly understood. Mutations or deficiencies in
these properties of stem cells, collectively considered “stemness,” lie at the heart of many
gastrointestinal disorders. Establishing a better understanding of the processes and transcription
factors that regulate stemness is critical to developing novel cellular and gene-based therapies for
those afflicted with GI disorders and cancers.Bachelor of Scienc
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Genetic Engineering to Investigate Driver Mutations of Gastrointestinal Neuroendocrine Tumors
Get PDFIn the intestine, rare neuroendocrine epithelial cells secrete hormones that aid the digestive process and modulate the immune response. Gastrointestinal neuroendocrine tumors (GI-NETs) are slow growing and comprised of cells that look similar to neuroendocrine cells. The Magness Lab has found that a subset of transit-amplifying (TA) cells found in the crypts of the small intestine have a gene expression signature with features of both stem and neuroendocrine cells. We hypothesize that oncogenic mutation(s) occurring in intestinal stem cells (ISCs) and/or TA cells keep endocrine progenitor cells derived from ISCs from exiting the cell cycle and fully differentiating. There is currently limited experimental evidence on the specific combination of mutations needed to induce GI-NET formation. However, human GI-NETs have been found to express a loss of function in the tumor suppressor MEN1 (Multiple Endocrine Neoplasia Type I) and high levels of SOX4 (Sry-Box 4), a transcription factor that promotes endocrine differentiation. This thesis investigated whether a MEN1 loss of function mutation alone drove NET phenotypes in human ISCs and progenitor cells. CRISPR-Cas9 gene editing was utilized to introduce the loss of function mutation in the MEN1 gene. MEN1+/- cells were characterized for GI-NET phenotypes, including an increase in endocrine marker ChgA and persistent proliferation despite the progression to a more differentiated enteroendocrine cell phenotype. The results showed that a MEN1+/- mutation is insufficient for increased proliferation or increased incidence of enteroendocrine differentiation. Future studies will involve testing cells with homozygous MEN1 mutations, SOX4 overexpression, and the combination of MEN1 and SOX4 mutations for signs of GI-NET formation. If successful, these studies will provide the first functional evidence for GI-NET driver mutations.Bachelor of Scienc
Crypts-on-a-Chip: Developing an ex vivo Model of the Intestinal Crypts
Get PDFCurrently, stem cell behavior following injury, inflammation, and viral/bacterial challenge is difficult to study in vivo due to the inability to control variables, limited human tissue resources, the prohibitive costs involved with animal studies, and/or the lack of cross-species infection by species-specific microbes. The goal of this thesis is to develop an ex vivo model of the gut epithelium and underlying mesenchyme to facilitate studies that are not possible due to these technical, ethical, and financial constraints. Microfabricated well arrays that mimic intestinal crypt dimensions demonstrated that PDLA, polystyrene, and 1002F promote proliferation of gut myofibroblasts more rapidly than PDMS. Methods were developed to enhance crypt seeding into microwells and standardize the isolation of epithelial tissue. Advanced 3-D imaging techniques using multi-photon excitation (MPE) and Imaris were also developed. These studies are a stepping stone in the development of an organ-on-a-chip for the intestine, and provide proof of concept for intestinal tissue engineering with microfabricated scaffolds
Variations on the Author
Get PDF“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
Investigating the Role of FoxA1 and FoxA2 as Candidate Transcriptional Regulators of Sox9 in Intestinal Crypt Stem Cells
Get PDFTwo stem cell states have been identified within the crypts of the small intestine: ‘quiescent’ and ‘active’. SOX9, a transcription factor encoded from the Sox9 gene has been hypothesized to be the master regulator between these ‘active’ (low expression of SOX9) and ‘reserve’ (high expression of SOX9) intestinal stem cell states. Therefore, putative cis-regulatory sequences upstream of the SOX9 promoter have been analyzed through TRANSFAC© to determine potential candidates for up-regulation of SOX9 in quiescent and active stem cells. Preliminary results indicate that FOXA1and A2 represent potential transcriptional regulators of the SOX9 gene. This hypothesis has been supported by immunohistochemistry, qRT-PCR analysis, and ChIP-sequencing demonstrating that FOXA1/2 co-expresses in cells that express high levels of SOX9 within the intestinal crypt. These studies provide further understanding of how stem cell identity is normally regulated in the cells of the intestinal crypt.Bachelor of Scienc
Intrinsic and extrinsic regulation of potency in the intestinal stem cell niche
Get PDFThe intestinal epithelium is one of the most proliferative tissues in the adult body, undergoing near total renewal every 5-7 days. This remarkable turnover is driven by a small population of intestinal stem cells (ISCs), which maintain the physiological function and epithelial barrier integrity of the small intestine, and initiate repair following damage. While the anatomical location of ISCs has been appreciated for decades, the complex genetics and cellular behavior of these cells is still the subject of intense research and debate. Emerging research shows that patterns of ISC proliferation and differentiation are governed by highly complex interactions between the extrinsic signaling of the ISC niche and intrinsic genetic programs that regulate ISC behavior on the cell-autonomous level. In this dissertation, we aim to address the regulation of ISC potency at the intrinsic and extrinsic levels. We describe technologic approaches for the isolation and in vitro culture of two distinct human ISC populations, as well as advanced, high-throughput culture conditions for the study of ISC-niche interactions. To address ISC potency from the perspective of intrinsic genetic programming, we examine the role of Sry-box containing 4 (Sox4), which we demonstrate plays a role in ISC differentiation and proliferation, possibly through epigenetic mechanisms. Together, these studies provide valuable tools for examining the effects of extrinsic signaling on ISC potency in vitro, as well as describe a novel mechanistic regulator of ISC differentiation.Doctor of Philosoph
Engineering a platform for increased BEST4+ cell differentiation and potential function
Get PDFBEST4+ cells (BPCs) are a newly identified human-specific intestinal epithelial cell type with largely unknown functions. This study aims to optimize BPC differentiation in vitro and investigate their role in ion transport, particularly zinc handling. Using human intestinal epithelial stem cells (hIESCs), we found that traditional transwell cultures contain low BPC numbers, but BPC differentiation can be enriched for through air-liquid interface (ALI) culture and a more acidic medium indicating pH sensitive differentiation. NOTCH and TGFB signaling and the overexpression of transcription factor BARX2, previously suspected to influence BPC differentiation, had no effect. To explore BPC function, we assessed their potential role in metal handling. BPCs highly express CNGA1, a nonspecific divalent cation channel, and metallothioneins, which are involved in metal homeostasis. Functional assays using a CNGA1- overexpressing HEK293 model showed increased intracellular zinc accumulation, demonstrating a role for CNGA1 in zinc transport. Furthermore, BPC-enriched ALI cultures exhibited elevated apical to basal zinc transport, supporting their involvement in epithelial metal handling. Finally, to facilitate real-time tracking of BPC differentiation, we generated a BEST4-iRFP reporter cell line, enabling live-cell visualization and fluorescence-based sorting. Collectively, our findings establish a robust method for BPC enrichment, demonstrate their pH sensitivity, and provide support for a potential function in metal ion transport. This work lays the foundation for future studies into BPC function and their potential contributions to gut homeostasis and disease.Bachelor of Scienc
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
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