Browsing by Subject "Proliferation"

Now showing 1 - 5 of 5

Characterizing miRNA mediated regulation of proliferation
(2014-05) Polioudakis, Damon Constantine; Iyer, Vishwanath R.
Cell proliferation is a fundamental biological process, and the ability of human cells to transition from a quiescent to proliferative state is essential for tissue homeostasis. Most cells in eukaryotic organisms are in a quiescent state, but on appropriate physiological or pathological stimuli, many types of somatic cells may exit quiescence, re-enter the cell cycle and begin to proliferate. The ability of cells to remain viable while quiescent, exit quiescence and re-enter into the cell cycle is the basis for varied physiological processes such as wound healing, lymphocyte activation and hepatocyte regeneration, but is also a hallmark of cancer. The transition of mammalian cells from quiescence to proliferation is accompanied by the differential expression of several microRNAs (miRNAs) and transcription factors. Our understanding of miRNA biology has significantly improved, but the miRNA regulatory networks that govern cell proliferation are still largely unknown. We characterized a miR-22 Myc network that mediates proliferation through regulation of the interferon response and multiple cell cycle arrest genes. We identified several cell cycle arrest genes that regulate the effects of the tumor suppressor p53 as direct targets of miR-22, and discovered that miR-22 suppresses interferon gene expression. We go on to show that miR-22 is activated by the transcription factor Myc as quiescent cells enter proliferation, and that miR-22 represses the Myc transcriptional repressor MXD4, mediating a feed forward loop to elevate Myc expression levels. To more effectively determine miRNA targets, we utilized a combination of RNA-induced silencing complex immunoprecipitations and gene expression profiling. Using this approach for miR-191, we constructed an extensive transcriptome wide miR-191 target set. We show that miR-191 regulates proliferation, and targets multiple proto-oncogenes, including CDK9, NOTCH2, and RPS6KA3. Recent advances in determining miRNA targetomes have revealed widespread non-canonical miRNA-target pairing. We experimentally identified the transcriptome wide targets of miR-503, miR-103, and miR-494, and observed evidence of non-canonical target pairing for these miRNAs. We went on to confirm that miR-503 requires pairing outside of the canonical 5' seed region to directly target the oncogene DDHD2. Further bioinformatics analysis implicated miR-503 and DDHD2 in breast cancer tumorigenesis.
Inhibitor of differentiation 2A influences growth and differentiation of the developing vertebrate retina upstream of the notch signaling pathway
(2012-08) Uribe, Rosa Anna; Gross, Jeffrey Martin; Vokes, Steven A.; Eberhart, Johann; Stein, David; Agarwala, Seema
Inhibitor of differentiation (Id) family helix-loop-helix proteins regulate the proliferation, survival and differentiation of numerous cell types during development, however their function during retinal development has not been analyzed. Using loss-of-function and overexpression assays in zebrafish, I demonstrate that Id2a levels modulate retinoblast cell cycle kinetics and thereby influence neuron and glia formation in the retina. Id2a-deficient retinas possess increased numbers of cells occupying S phase, at the expense of mitotic cells, and kinetic analyses demonstrate that Id2a is required for S-phase progression and/or the transition from S to M phase. Id2a-dependent defects in retinoblast proliferation lead to microphthalmia and to an absence of nearly all differentiated inner and outer nuclear layer cell types. Overexpression of id2a has the opposite effect on retinoblast cell cycle kinetics: id2a-overexpressing retinoblasts progress from S to M phase more rapidly and they undergo mitosis more frequently, which results in macrophthalmia. Mosaic analyses reveal that Id2a function in facilitating both cell cycle progression and neuronal differentiation in the retina is non-cell-autonomous, suggesting that Id2a functions upstream of the extrinsic pathways that regulate retinogenesis. In an effort to identify which extrinsic pathways function downstream of Id2a, I discovered that Id2a function is necessary and sufficient to limit Notch pathway activity during retinogenesis. Id2a-deficient retinae possess elevated levels of Notch pathway component gene expression, while retinae overexpressing id2a possess reduced expression of Notch pathway component genes. Attenuation of Notch signaling activity by DAPT or by morpholino knockdown of Notch1a is sufficient to rescue both the proliferative and differentiation defects in Id2a-deficient retinae. In addition to regulating Notch pathway activity, through an RNA-Seq and differential gene expression analysis of Id2a-deficient retinae, I identified a number of additional intrinsic and extrinsic regulatory pathway components whose expression is regulated by Id2a. These data highlight the integral role played by Id2a in the gene regulatory network governing the transition from retinoblast proliferation to terminal differentiation during vertebrate retinogenesis.
Plutonium for Energy? Explaining the Global Decline of MOX
(2018-10-22) Kuperman, Alan J.
Plutonium is a controversial fuel for three reasons: it causes cancer, may be used in nuclear weapons, and is very expensive to obtain and process. Yet, relatively little information has been publicly available about the attempted commercialization of plutonium fuel around the world in the last several decades. This book is the first comprehensive global study of “plutonium for energy” – the use of mixed-oxide (MOX) fuel in light-water nuclear power reactors that traditionally had used uranium fuel – and is based on field research in all seven countries that have engaged in the commercial production or use of such fuel. The book finds an industry in rapid decline, as five of the countries already have decided to phase out commercial MOX activities, while five of the world’s six commercial production facilities for such MOX fuel have closed prematurely after underperforming. This retreat is attributed to plutonium’s three inherent downsides – safety, security, and cost – which make MOX fuel significantly more expensive, dangerous, and unpopular than traditional uranium fuel. The book includes chapters on Belgium, France, Germany, Japan, the Netherlands, Switzerland, and the United Kingdom. Its introductory chapter highlights the lessons from these historical cases for countries that are currently contemplating the initiation or expansion of using plutonium fuel – including China, India, Japan, Russia, South Korea, the United Kingdom, and the United States.
Priorities and constraints : presidential decision making and nuclear nonproliferation policy in the first decade of the NPT
(2016-12) Reiss, Megan Ann; Inboden, William, 1972-; Suri, Jeremi; Lawrence, Mark; Buchanan, Bruce; Chesney, Robert
The signing and ratification of the Nuclear Nonproliferation Treaty (NPT) had the potential to be an inflection point in presidential decision making regarding nonproliferation policy. The norm-creating treaty was a new tool for presidents to use to prevent the spread of nuclear weapons and reduce the possibility that states would someday participate in a nuclear war. However, the NPT had only a limited impact on presidential nonproliferation policy in the years after the implementation of the treaty, and it failed to lead to a standard response to proliferation challenges. While most attempts to understand U.S. nuclear policy after the enactment of the NPT center on arms control, this dissertation explores why and how presidents developed nonproliferation policy in the decade after the signing and ratification of the NPT. It is an historical analysis of how and why presidents made decisions to either prioritize or deprioritize nonproliferation policy as compared to pursuing other objectives. Presidential preferences for nonproliferation varied greatly depending on their personal commitments to nonproliferation as well as their calculations of threats that stemmed from proliferation. Other actors like Congress, the public, the nuclear industry, the Soviet Union, and allies placed restraints on the president’s ability to enact his preferences. Although Congress generally gives the president a large amount of leverage in determining the direction of foreign policy, it proved to be a particularly strong domestic check on presidential preferences for nuclear policy. Geopolitical objectives, especially Cold War goals, overwhelmed presidential preference for nonproliferation policy. When nonproliferation goals aligned with Cold War objectives, presidents directed resources towards achieving those goals; however, if pursuing a nonproliferation policy would reduce American power or its ability to compete with the Soviet Union, presidents repeatedly deprioritized nonproliferation goals in favor of Cold War objectives.
The role of Twist1 in UVB-induced skin carcinogenesis
(2021-03-14) Eguiarte-Solomon, Fernando; DiGiovanni, John; Vasquez, Karen; Tiziani, Stefano; Kidane-Mulat, Dawit
The transcription factor Twist1 has been reported to be essential for the formation and invasiveness of chemically induced tumors in mouse skin. However, the impact of keratinocyte specific Twist1 deletion on carcinogenesis caused by UVB radiation has not been clarified. In the current studies, we demonstrate that deletion of Twist1 in skin keratinocytes in vivo (using K5-Cre x Twist1[superscript flox/flox] mice; Twist1 KO mice) significantly suppressed UVB-induced skin carcinogenesis. Twist1 KO led to reduced UVB-induced epidermal hyperproliferation. Proliferation analysis by Ki67 immunofluorescence staining as well as BrdU incorporation showed a significant decrease in Twist1 KO epidermis. In addition, Twist1 was also found to control the differentiation of keratinocytes in the bulge region and in the interfollicular epidermis, suggesting that exit from cell cycle in Twist1 KO keratinocytes is linked to induction of differentiation. Deletion of Twist1 in vivo and in culture showed significant induction of early and late differentiation markers including TG1, K1, OVOL1, Loricrin and Filaggrin. In contrast, overexpression of Twist1 in cultured keratinocytes suppressed expression of calcium-induced differentiation markers. Additionally, deletion of Twist1 in epidermal and bulge region keratinocytes led to depletion of several hair follicle stem/progenitor markers, including CD34, Lrig1, Lgr5 and Lgr6. These findings further support the hypothesis that Twist1 may have direct role in regulating proliferation, differentiation and self-renewal processes in the epidermis. We also discovered that the natural compound, Harmine, leads to degradation of Twist1 in keratinocytes and inhibits UVB-induced epidermal proliferation while stimulating keratinocyte differentiation similar to Twist1 KO. Collectively, the current data demonstrate an important role for Twist1 in UVB skin carcinogenesis and the potential for this transcription factor as a target for skin cancer prevention