Search NASA⌕ Search

SEARCH · Search NASA

Results for “STEM”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Methane emissions from tree stems: a new frontier in the global carbon cycle

Tree stems from wetland, floodplain and upland forests can produce and emit methane (CH 4 ). Tree CH 4 stem emissions have high spatial and temporal variability, but there is no consensus on the biophysical mechanisms that drive stem CH 4 production and emissions. Here, we summarize up to 30 opportunities and challenges for stem CH 4 emissions research, which when addressed will improve estimates of magnitudes, patterns, drivers and trace the potential origin of CH 4 emissions. We identified the need (i) for both long–term high frequency measurements of stem CH 4 emissions to understand the fine scale processes, alongside rapid large–scale measurements designed to understand variability across individuals, species and ecosystems; (ii) to identify microorganisms and biogeochemical pathways associated with CH 4 production; and (iii) to develop a mechanistic model including passive and active transport of CH 4 from the soil–tree–atmosphere continuum. Addressing these challenges would help to constrain magnitudes and patterns of CH 4 emissions, and would allow for the integration of pathways and mechanisms of CH 4 production and emissions into process–based models. As a result, these advances will facilitate upscaling of stem CH 4 emissions to the ecosystem level and quantify the role of stem CH 4 emissions for the local–to–global CH 4 budget.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2013

Impact of Mesenchymal Stem Cell secreted PAI-1 on colon cancer cell migration and proliferation

Highlights: •MSCs were directly co-cultured with colorectal cancer (CRC) cells on 3D scaffolds. •MSCs influence CRC protein/gene expression, proliferation and migration. •We report a significant functional role of MSC-secreted PAI-1 in colon cancer. -- Abstract: Mesenchymal Stem Cells are known to engraft and integrate into the architecture of colorectal tumours, with little known regarding their fate following engraftment. This study aimed to investigate mediators of Mesenchymal Stem Cell (MSC) and colon cancer cell (CCC) interactions. Mesenchymal Stem Cells and colon cancer cells (HT29 and HCT-116) were cultured individually or in co-culture on 3-dimensional scaffolds. Conditioned media containing all secreted factors was harvested at day 1, 3 and 7. Chemokine secretion and expression were analyzed by Chemi-array, ELISA (Macrophage migration inhibitory factor (MIF), plasminogen activator inhibitor type 1 (PAI-1)) and RQ-PCR. Colon cancer cell migration and proliferation in response to recombinant PAI-1, MSCs and MSCs + antibody to PAI-1 was analyzed using Transwell inserts and an MTS proliferation assay respectively. Chemi-array revealed secretion of a wide range of factors by each cell population, including PAI-1and MIF. ELISA analysis revealed Mesenchymal Stem Cells to secrete the highest levels of PAI-1 (MSC mean 10.6 ng/mL, CCC mean 1.01 ng/mL), while colon cancer cells were the principal source of MIF. MSC-secreted PAI-1 stimulated significant migration of both CCC lines, with an antibody to the chemokine shown to block this effect (67–88% blocking,). A cell-line dependant effect on CCC proliferation was shown for Mesenchymal Stem Cell-secreted PAI-1 with HCT-116 cells showing decreased proliferation at all concentrations, and HT29 cells showing increased proliferation in the presence of higher PAI-1 levels. This is the first study to identify PAI-1 as an important mediator of Mesenchymal Stem Cell/colon cancer cell interactions and highlights the significant functional impact of Mesenchymal Stem Cell-secreted PAI-1 on colon cancer cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

DDX4 (DEAD box polypeptide 4) colocalizes with cancer stem cell marker CD133 in ovarian cancers

Highlights: • Germ cell marker DDX4 was significantly increased in ovarian cancer. • Ovarian cancer stem cell marker CD133 was significantly increased in ovarian cancer. • DDX4 and CD133 were mostly colocalized in various types of ovarian cancer tissues. • CD133 positive ovarian cancer cells also express DDX4 whereas CD133-negative cells did not possess DDX4. • Germ cell marker DDX4 has the potential of ovarian cancer stem cell marker. - Abstract: DDX4 (DEAD box polypeptide 4), characterized by the conserved motif Asp-Glu-Ala-Asp (DEAD), is an RNA helicase which is implicated in various cellular processes involving the alteration of RNA secondary structure, such as translation initiation, nuclear and mitochondrial splicing, and ribosome and spliceosome assembly. DDX4 is known to be a germ cell-specific protein and is used as a sorting marker of germline stem cells for the production of oocytes. A recent report about DDX4 in ovarian cancer showed that DDX4 is overexpressed in epithelial ovarian cancer and disrupts a DNA damage-induced G2 checkpoint. We investigated the relationship between DDX4 and ovarian cancer stem cells by analyzing the expression patterns of DDX4 and the cancer stem cell marker CD133 in ovarian cancers via tissue microarray. Both DDX4 and CD133 were significantly increased in ovarian cancer compared to benign tumors, and showed similar patterns of expression. In addition, DDX4 and CD133 were mostly colocalized in various types of ovarian cancer tissues. Furthermore, almost all CD133 positive ovarian cancer cells also express DDX4 whereas CD133-negative cells did not possess DDX4, suggesting a strong possibility that DDX4 plays an important role in cancer stem cells, and/or can be used as an ovarian cancer stem cell marker.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Longitudinal monitoring adipose-derived stem cell survival by PET imaging hexadecyl-4-{sup 124}I-iodobenzoate in rat myocardial infarction model

Highlights: • We developed a safe, simple and appropriate stem cell labeling method with {sup 124}I-HIB. • ADSC survival can be monitored with PET in MI model via direct labeling. • Tracking of ADSC labeled with {sup 124}I-HIB was possible for 3 days in MI model using PET. • ADSC viability and differentiation were not affected by {sup 124}I-HIB labeling. • Survival of ADSC in living bodies can be longitudinally tracked with PET imaging. - Abstract: This study aims to monitor how the change of cell survival of transplanted adipose-derived stem cells (ADSCs) responds to myocardial infarction (MI) via the hexadecyl-4-{sup 124}I-iodobenzoate ({sup 124}I-HIB) mediated direct labeling method in vivo. Stem cells have shown the potential to improve cardiac function after MI. However, monitoring of the fate of transplanted stem cells at target sites is still unclear. Rat ADSCs were labeled with {sup 124}I-HIB, and radiolabeled ADSCs were transplanted into the myocardium of normal and MI model. In the group of {sup 124}I-HIB-labeled ADSC transplantation, in vivo imaging was performed using small-animal positron emission tomography (PET)/computed tomography (CT) for 9 days. Twenty-one days post-transplantation, histopathological analysis and apoptosis assay were performed. ADSC viability and differentiation were not affected by {sup 124}I-HIB labeling. In vivo tracking of the {sup 124}I-HIB-labeled ADSCs was possible for 9 and 3 days in normal and MI model, respectively. Apoptosis of transplanted cells increased in the MI model compared than that in normal model. We developed a direct labeling agent, {sup 124}I-HIB, and first tried to longitudinally monitor transplanted stem cell to MI. This approach may provide new insights on the roles of stem cell monitoring in living bodies for stem cell therapy from pre-clinical studies to clinical trials.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Local calcium signalling is mediated by mechanosensitive ion channels in mesenchymal stem cells

Mechanical forces are implicated in key physiological processes in stem cells, including proliferation, differentiation and lineage switching. To date, there is an evident lack of understanding of how external mechanical cues are coupled with calcium signalling in stem cells. Mechanical reactions are of particular interest in adult mesenchymal stem cells because of their promising potential for use in tissue remodelling and clinical therapy. Here, single channel patch-clamp technique was employed to search for cation channels involved in mechanosensitivity in mesenchymal endometrial-derived stem cells (hMESCs). Functional expression of native mechanosensitive stretch-activated channels (SACs) and calcium-sensitive potassium channels of different conductances in hMESCs was shown. Single current analysis of stretch-induced channel activity revealed functional coupling of SACs and BK channels in plasma membrane. The combination of cell-attached and inside-out experiments have indicated that highly localized Ca{sup 2+} entry via SACs triggers BK channel activity. At the same time, SK channels are not coupled with SACs despite of high calcium sensitivity as compared to BK. Our data demonstrate novel mechanism controlling BK channel activity in native cells. We conclude that SACs and BK channels are clusterized in functional mechanosensitive domains in the plasma membrane of hMESCs. Co-clustering of ion channels may significantly contribute to mechano-dependent calcium signalling in stem cells. - Highlights: • Stretch-induced channel activity in human mesenchymal stem cells was analyzed. • Functional expression of SACs and Ca{sup 2+}-sensitive BK and SK channels was shown. • Local Ca{sup 2+} influx via stretch-activated channels triggers BK channel activity. • SK channels are not coupled with SACs despite higher sensitivity to [Ca{sup 2+}]{sub i}. • Functional clustering of SACs and BK channels in stem cell membrane is proposed.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

MiR-129-5p inhibits non-small cell lung cancer cell stemness and chemoresistance through targeting DLK1

Non-small cell lung cancer (NSCLC) stemness and chemoresistance represent significant barriers to successful treatment. Downregulation of microRNA 129 (miR-129) has been implicated in a variety of cancers, and miR-129-5p has recently been shown to reduce lung cancer proliferation and metastasis. In this study, we used NSCLC cell lines A549 and H460 to investigate the effects of miR-129-5p on NSCLC stemness and chemoresistance. CD133 + stem cells in both lines showed reduced miR-129-5p expression, and introducing miR-129-5p into these cells reduced stem cell markers and self-renewal ability, as measured by qRT-PCR, western blot, MTT assays, and sphere formation assays. MTT, colony formation, and DAPI staining assays further revealed that miR-129-5p inhibits NSCLC chemoresistance when the cells are treated with varying doses of CDDP. The target prediction algorithm TargetScan allowed us to identify notch signaling receptor delta-like 1 homolog (DLK1) as a potential target for miR-129-5p in its inhibition of NSCLC stemness and chemoresistance. Indeed, our DLK1 luciferase reporter plasmid demonstrated that miR-129-5p reduces DLK1 expression. Furthermore, DLK1 overexpression partially rescued inhibition of NSCLC stemness and chemoresistance caused by miR-129-5p. Overall, these results demonstrate that miR-129-5p inhibits NSCLC stemness and chemoresistance through direct targeting of DLK1. They suggest that miR-129-5p and DLK1 can play a role in an effective treatment strategy for NSCLC.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Loss of fructose-1,6-bisphosphatase induces glycolysis and promotes apoptosis resistance of cancer stem-like cells: an important role in hexavalent chromium-induced carcinogenesis

Hexavalent chromium (Cr(VI)) compounds are confirmed human carcinogens for lung cancer. Our previous studies has demonstrated that chronic exposure of human bronchial epithelial BEAS-2B cells to low dose of Cr(VI) causes malignant cell transformation. The acquisition of cancer stem cell-like properties is involved in the initiation of cancers. The present study has observed that a small population of cancer stem-like cells (BEAS-2B-Cr-CSC) exists in the Cr(VI)-transformed cells (BEAS-2B-Cr). Those BEAS-2B-Cr-CSC exhibit extremely reduced capability of generating reactive oxygen species (ROS) and apoptosis resistance. BEAS-2B-Cr-CSC are metabolic inactive as evidenced by reductions in oxygen consumption, glucose uptake, ATP production, and lactate production. Most importantly, BEAS-2B-Cr-CSC are more tumorigenic with high levels of cell self-renewal genes, Notch1 and p21. Further study has found that fructose-1,6-bisphosphatase (FBP1), an rate-limiting enzyme driving glyconeogenesis, was lost in BEAS-2B-Cr-CSC. Forced expression of FBP1 in BEAS-2B-Cr-CSC restored ROS generation, resulting in increased apoptosis, leading to inhibition of tumorigenesis. In summary, the present study suggests that loss of FBP1 is a critical event in tumorigenesis of Cr(VI)-transformed cells. - Highlights: • A small population of cancer-like stem cells exist in Cr(VI)-transformed cells. • Those cancer-like stem cells are low in ROS levels and resistant to apoptosis. • Those cancer-like stem cells are metabolic inactive and loss of FBP1. • Those cancer-like stem cells initiate and sustain tumor growth. • Forced expression of FBP1 inhibits tumorigenecity of those cancer-like stem cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Transforming growth factor-beta1 promotes the migration and invasion of sphere-forming stem-like cell subpopulations in esophageal cancer

Esophageal cancer is one of the most lethal solid malignancies. Mounting evidence demonstrates that cancer stem cells (CSCs) are able to cause tumor initiation, metastasis and responsible for chemotherapy and radiotherapy failures. As CSCs are thought to be the main reason of therapeutic failure, these cells must be effectively targeted to elicit long-lasting therapeutic responses. We aimed to enrich and identify the esophageal cancer cell subpopulation with stem-like properties and help to develop new target therapy strategies for CSCs. Here, we found esophageal cancer cells KYSE70 and TE1 could form spheres in ultra low attachment surface culture and be serially passaged. Sphere-forming cells could redifferentiate and acquire morphology comparable to parental cells, when return to adherent culture. The sphere-forming cells possessed the key criteria that define CSCs: persistent self-renewal, overexpression of stemness genes (SOX2, ALDH1A1 and KLF4), reduced expression of differentiation marker CK4, chemoresistance, strong invasion and enhanced tumorigenic potential. SB525334, transforming growth factor-beta 1(TGF-β1) inhibitor, significantly inhibited migration and invasion of sphere-forming stem-like cells and had no effect on sphere-forming ability. In conclusion, esophageal cancer sphere-forming cells from KYSE70 and TE1 cultured in ultra low attachment surface possess cancer stem cell properties, providing a model for CSCs targeted therapy. TGF-β1 promotes the migration and invasion of sphere-forming stem-like cells, which may guide future studies on therapeutic strategies targeting these cells. - Highlights: • Esophageal cancer sphere-forming cells possess cancer stem cell properties. • Sphere-forming cells enhance TGF-β1 pathway activity. • TGF-β 1 inhibitor suppresses the migration and invasion of sphere-forming cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

In vitro cementoblast-like differentiation of postmigratory neural crest-derived p75{sup +} stem cells with dental follicle cell conditioned medium

Cranial neural crest-derived cells (CNCCs) play important role in epithelial–mesenchymal interactions during tooth morphogenesis. However, the heterogeneity of CNCCs and their tendency to spontaneously differentiate along smooth muscle or osteoblast lineages in vitro limit further understanding of their biological properties. We studied the differentiation properties of isolated rat embryonic postmigratory CNCCs, expressing p75 neurotrophin receptor (p75NTR). These p75NTR positive (p75{sup +}) CNCCs, isolated using fluorescence activated cell sorter, exhibited fibroblast-like morphology and characteristics of mesenchymal stem cells. Incubation of p75{sup +} CNCCs in dental follicle cell conditioned medium (DFCCM) combined with dentin non-collagenous proteins (dNCPs), altered their morphological features to cementoblast-like appearance. These cells also showed low proliferative activity, high ALP activity and significantly increased calcified nodule formation. Markers related to mineralization or specific to cementoblast lineage were highly expressed in dNCPs/DFCCM-treated p75{sup +} cells, suggesting their differentiation along cementoblast-like lineage. p75{sup +} stem cells selected from postmigratory CNCCs represent a pure stem cell population and could be used as a stem cell model for in vitro studies due to their intrinsic ability to differentiate to neuronal cells and transform from neuroectoderm to ectomesenchyme. They can provide a potential stem cell resource for tooth engineering studies and help to further investigate mechanisms of epithelial–mesenchymal interactions in tooth morphogenesis. - Highlights: • Cranial neural crest-derived cells (CNCCs) take part in tooth morphogenesis. • positive (p75{sup +}) CNCCs are fibroblast-like and resemble mesenchymal stem cells. • p75{sup +} CNCCs in dental follicle cell medium (DFCCM/dNCP) appear like cementoblasts. • DFCCM/dNCP-treated p75{sup +} cells express cementoblast specific mineralization markers. • p75{sup +} cells are pure stem cells and able to differentiate to neuronal cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

In vitro and in vivo characterization of stem-like cells from canine osteosarcoma and assessment of drug sensitivity

Highlights: • Canine osteosarcoma are enriched in cancer stem cells. • Canine osteosarcoma stem cells are tumorigenic in vivo. • Standard first-line drugs for osteosarcoma affect cancer stem cells cultures. • Metformin inhibits viability and self-renewal of osteosarcoma stem cells. • Canine osteosarcoma stem cells are reliable experimental model to assay drug efficacy. Cancer stem cell (CSC) self-renewing and drug resistance cause treatment failure and tumor recurrence. Osteosarcoma is an aggressive bone tumor characterized by biological and molecular heterogeneity, possibly dependent on CSCs. CSC identification in osteosarcoma and their efficient targeting are still open questions. Spontaneous canine osteosarcoma shares clinical and biological features with the human tumors, representing a model for translational studies. We characterized three CSC-enriched canine osteosarcoma cultures. In serum-free conditions, these CSC cultures grow as anchorage-independent spheroids, show mesenchymal-like properties and in vivo tumorigenicity, recapitulating the heterogeneity of the original osteosarcoma. Osteosarcoma CSCs express stem-related factors (Sox2, Oct4, CD133) and chemokine receptors and ligands (CXCR4, CXCL12) involved in tumor proliferation and self-renewal. Standard drugs for osteosarcoma treatment (doxorubicin and cisplatin) affected CSC-enriched and parental primary cultures, showing different efficacy within tumors. Moreover, metformin, a type-2 diabetes drug, significantly inhibits osteosarcoma CSC viability, migration and self-renewal and, in co-treatment with doxorubicin and cisplatin, enhances drug cytotoxicity. Collectively, we demonstrate that canine osteosarcoma primary cultures contain CSCs exhibiting distinctive sensitivity to anticancer agents, as a reliable experimental model to assay drug efficacy. We also provide proof-of-principle of metformin efficacy, alone or in combination, as pharmacological strategy to target osteosarcoma CSCs.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

DYRK1A is required for maintenance of cancer stemness, contributing to tumorigenic potential in oral/oropharyngeal squamous cell carcinoma

Highlights: • DYRK1A is essential to maintain cancer stemness in OSCC. • DYRK1A regulates cancer stemness via FGF2 expression. • Levels of DYRK1A and FGF2 expression are positively correlated in OSCC cells. • DYRK1A-FGF2 is a novel molecular axis regulating cancer stemness in OSCC. DYRK1A, one of the dual-specificity tyrosine phosphorylation-regulated kinases (DYRKs), plays an important role in various biological processes by regulating downstream targets via kinase-dependent and independent mechanisms. Here, we report a novel role of DYRK1A in maintaining tumor growth and stemness of oral/oropharyngeal squamous cell carcinoma (OSCC) cells. Deletion of DYRK1A from OSCC cells abrogated their in vivo tumorigenicity and self-renewal capacity, the key features of cancer stem-like cells (CSCs; also referred to as tumor-initiating cells). The DYRK1A deletion also induced the suppression of CSC populations and properties, such as migration ability and chemoresistance. Conversely, ectopic expression of DYRK1A in OSCC cells augmented their CSC phenotype. Among five DYRK members (DYRK1A, 1B, 2, 3, and 4), DYRK1A is the most dominantly expressed kinase, and its expression is upregulated in OSCC compared to normal oral epithelial cells. More importantly, DYRK1A was highly enriched in various CSC-enriched OSCC populations compared to their corresponding non-CSC populations, indicating its pivotal role in cancer progression and stemness. Further, our study revealed that fibroblast growth factor 2 (FGF2) is a key regulator in the DYRK1A-mediated CSC regulation. Functional studies demonstrated that the loss of DYRK1A inhibits CSC phenotype via reduction of FGF2. Overexpression of DYRK1A promotes CSC phenotype via upregulation of FGF2. Our study delineates a novel mechanism of cancer stemness regulation by DYRK1A-FGF2 axis in OSCC. Thus, inhibition of DYRK1A would lead to a potential novel therapeutic option for targeting CSCs in OSCC.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

An empirical method that separates irreversible stem radial growth from bark water content changes in trees: theory and case studies

Substantial uncertainty surrounds our knowledge of tree stem growth, with some of the most basic questions, such as when stem radial growth occurs through the daily cycle, still unanswered. Here, we employed high-resolution point dendrometers, sap flow sensors, and developed theory and statistical approaches, to devise a novel method separating irreversible radial growth from elastic tension-driven and elastic osmotically driven changes in bark water content. We tested this method using data from five case study species. Experimental manipulations, namely a field irrigation experiment on Scots pine and a stem girdling experiment on red forest gum trees, were used to validate the theory. Time courses of stem radial growth following irrigation and stem girdling were consistent with a-priori predictions. Patterns of stem radial growth varied across case studies, with growth occurring during the day and/or night, consistent with the available literature. Importantly, our approach provides a valuable alternative to existing methods, as it can be approximated by a simple empirical interpolation routine that derives irreversible radial growth using standard regression techniques. In conclusion, our novel method provides an improved understanding of the relative source–sink carbon dynamics of tree stems at a sub-daily time scale.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Cheyney University Curriculum and Infrastructure Enhamcement in STEM

Cheyney University is the oldest historically Black educational institution in America. Initially established as a “normal” school emphasizing the matriculation of educators, Cheyney has become a comprehensive university, one of 14 state universities comprising the Pennsylvania State System of Higher Education (PASSHE). Cheyney University graduates still become teachers, but they also enter such fields as journalism, medicine, science, mathematics, law, communication and government. Cheyney University is a small state owned HBCU with very limited resource. At present the university has about a thousand students with 15% in STEM. The CUCIES II grant made significant contribution in saving the computer science program from being a discontinued program in the university. The grant enabled the university to hire a temporary faculty to teach in and update the computer science program. The program is enhanced with three tracks; cyber security, human computer interaction and general. The updated and enhanced computer science program will prepare professionals in the area of computer science with the knowledge, skills, and professional ethic needed for the current market. The new curriculum was developed for a professional profile that would focus on the technologies and techniques currently used in the industry. With faculty on board, the university worked with the department to bring back the computer science program from moratorium. Once in the path of being discontinued and loosing students, the program is now growing. Currently the student number has increased from 12 to 30. University is currently in the process of hiring a tenure track faculty in the computer science program. Another product of the grant is the proposal for introductory course in nanotechnology. The course is intended to generate interest in the nanotechnology field. The Natural and Applied Science department that houses all of the STEM programs in Cheyney University, is currently working to bring back environmental science program from moratorium. The university has been working to improve minority participation in STEM and made significant stride in terms of progressing students toward graduate programs and into professoriate track. This success is due to faculty mentors who work closely with students to guiding them through the application processes for research internship and graduate programs; it is also due to the university forming collaborative agreements with research intensive institutions, federal and state agencies and industry. The grant assisted in recruiting and retaining students in STEM by offering tuition scholarship, research scholarship and travel awards. Faculty professional development was supported by the grant by funding travel to conferences, meetings and webinar. As many HBCU Cheyney University is also trying to do more with less. As the STEM programs are inherently expensive, these are the ones that suffer more when resources are scarce. One of the goals of Cheyney University strategic plan is to strengthen STEM programs that is coherent with the critical skill need of Department of Energy. All of the Cheyney University STEM programs are now located in the new science building funded by Pennsylvania state.

99 GENERAL AND MISCELLANEOUS↗
NASA NTRS2017

The Role of CDKN1a/p21 in Cellular Senescence of Bone Marrow Stem Cells Under Spaceflight Stressors

Spaceflight environments and their associated conditions, such as microgravity and space radiation, cause many biological functions formerly considered to be standard to behave in nonstandard ways. Exposure to microgravity has shown to induce deleterious effects in stem cell-based tissue regeneration, leading to immune system and healing response impairments as well as muscle and bone density loss. Such risks must be mitigated in order for long-term human space exploration to proceed. Thus, our work seeks to explore mechanisms of stem cell-based tissue regeneration that experience changes in spaceflight environments. Cellular senescence is a process of inducing cell cycle arrest that can be initiated by various stimuli. This function is influenced by two major pathways, controlled by p53 and pRB tumor suppressor proteins. p53 activity targets the cyclin-dependent kinase inhibitor gene p21Cdkn1a in osteogenic cell cycle arrest. Under conditions of mechanical unloading, stem cell-based tissue regeneration has shown to be decreased in both proliferation and differentiation, as many cells are arrested in progenitor states. p21 has shown upregulation in expression under conditions of microgravity, suggesting its role in regenerative bone formation arrest in space. p21 levels are found to be elevated independent of p53, suggesting a decrease in proliferation and regeneration without apoptosis, but rather through cell cycle arrest alone. Thus, we hypothesize that p21 is a mediator of cellular senescence in bone marrow stem cells. Culturing of bone marrow stem cells from wild type and p21 knockout mice under osteoblastogenic conditions will be completed to explore the role of p21Cdkn1a in stem cell proliferation and maturation. We believe that decreases in somatic stem cell differentiation may occur after spaceflight due to signal pathway alterations that result in downstream inhibition of genes involved in differentiation, preventing tissue from repairing and regenerating normally.

Stem Cells↗
DOE OSTI2021

A Fast Algorithm for Scanning Transmission Electron Microscopy Imaging and 4D-STEM Diffraction Simulations

Scanning transmission electron microscopy (STEM) is an extremely versatile method for studying materials on the atomic scale. Many STEM experiments are supported or validated with electron scattering simulations. However, using the conventional multislice algorithm to perform these simulations can require extremely large calculation times, particularly for experiments with millions of probe positions as each probe position must be simulated independently. Recently, the plane-wave reciprocal-space interpolated scattering matrix (PRISM) algorithm was developed to reduce calculation times for large STEM simulations. Here, we introduce a new method for STEM simulation: partitioning of the STEM probe into “beamlets,” given by a natural neighbor interpolation of the parent beams. This idea is compatible with PRISM simulations and can lead to even larger improvements in simulation time, as well requiring significantly less computer random access memory (RAM). We have performed various simulations to demonstrate the advantages and disadvantages of partitioned PRISM STEM simulations. We find that this new algorithm is particularly useful for 4D-STEM simulations of large fields of view. We also provide a reference implementation of the multislice, PRISM, and partitioned PRISM algorithms.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Brachypodium as an experimental system for the study of stem parenchyma biology in grasses

Stem parenchyma is a major cell type that serves key metabolic functions for the plant especially in large grasses, such as sugarcane and sweet sorghum, where it serves to store sucrose or other products of photosynthesis. It is therefore desirable to understand the metabolism of this cell type as well as the mechanisms by which it provides its function for the rest of the plant. Ultimately, this information can be used to selectively manipulate this cell type in a controlled manner to achieve crop improvement. In this study, we show that Brachypodium distachyon is a useful model system for stem pith parenchyma biology. Brachypodium can be grown under condition where it resembles the growth patterns of important crops in that it produces large amounts of stem material with the lower leaves senescing and with significant stores of photosynthate located in the stem parenchyma cell types. We further characterize stem plastid morphology as a function of tissue types, as this organelle is central for a number of metabolic pathways, and quantify gene expression for the four main classes of starch biosynthetic genes. Notably, we find several of these genes differentially regulated between stem and leaf. Furthermore, these studies show, consistent with other grasses, that the stem functions as a specialized storage compartment in Brachypodium.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Stem CO2 Efflux measurements from Manaus, Brazil, 2017

This data was collected in order to test the effects of temperatures on the autotrophic respiratory process in the tropics. This data package contains raw real-time stem CO2 efflux files during the night and day from 3 different species near the K34 in Manaus during the day and the night. Raw and derived data files are included in the format of .csv and .xlsx and information about the canopy trees and temperatures recorded can be found in the field event log using microsoft excel. The data was collected from three canopy dominant trees in the central Amazon near the K34 tower. Real-time stem CO2 efflux was determined using a Li7000 gas analyzer configured in differential mode and connected to a dynamic stem chamber secured to the stem at breast height using straps to generate a reasonable seal. Ambient air was continuously pumped into the stem chamber and CO2 concentrations of the air entering and exiting the chamber were continuously monitored. CO2 efflux was calculated based on the CO2 concentration difference between ambient and stem chambers, the flow rate of air through the chamber, and the area of the enclosed stem. Additional auxiliary data, including sap flow and crown temperature were also measured. No data processing or QA/QC was done on the raw data packages.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

STEM Imaging of Materials: Final Report for DE-FG02-08ER46547

This project supported research advancing the state of the art in scanning transmission electron microscopy (STEM) imaging and characterization of materials, especially electronic materials. The project began with studies of point defects in materials using high-resolution Z-contrast STEM, then evolved to including methods in four-dimensional (4D) STEM and machine learning. Highlights include: (1) the discovery of stable, p-type ZnO via Sb doping, (2) demonstration that the high performance of InGaN LEDs is not due to In composition fluctuations as previously proposed, (3) the demonstration of the first sub-pm precision high-resolution STEM images using non-rigid registration of a series of STEM images, (4) the extension of high-precision STEM to low dose imaging and spectrum imaging, (5) discovery of a synthesis method for twisted spiral growth of transition-metal dichalcogenide materials via chemical vapor deposition, and (6) development of machine-learning methods for analysis and denoising of enormous 4D STEM data sets.

36 MATERIALS SCIENCE↗