352 research outputs found
Neural stem cells and their contribution to neurogenesis in the adult mammalian brain
No full textFor a long time it was believed that neurogenesis in the mammalian central nervous system was restricted to the embryonic and early postnatal period. Almost four decades ago Altman and colleagues challenged this notion, but it took more than thirty years before new studies with refined methods convincingly demonstrated neurogenesis in the adult mammalian brain, including the adult monkey and human brain. Another major discovery was the demonstration by Reynolds and Weiss (1992) that neural stem cells persist in the mature brain that could be grown in culture and had the hallmark properties of stem cells: multipotency and self-renewal capacity. An obvious question following the discovery of stem cells in the adult brain was the localization and identity of these cells. We tested the hypothesis if ependymal cells, which delineate the ventricular system, might be a neural stem cell population in the adult brain.Ependymal cells were labeled in vivo, using either the fluoroescent label DiI or an adenovirus expressing the reporter gene lacZ. Immediately following an intraventricular injection, labeling was restricted to ependymal cells. At later timepoints labeled cells could be observed to enter the migratory stream to the olfactory bulb. There they differentiated into neurons as demonstrated by double labeling with neuronal markers. Based on fluorescent labeling and on their specific morphology single ependymal cells could be isolated, cultured and induced to differentiate into the major cell types of the CNS. Exploiting the fact that ependymal cells express the notch- I receptor on their surface, neural stem cells could be enriched by magnetic sorting. Long term labeling of cells in the subventricular zone and the spinal cord with BrdU revealed that neural stem cells are slowly dividing. After a traumatic injury to the spinal cord however, proliferation of ependymal cells increased. Newborn cells migrated from the central canal to the site of injury where they contributed to the formation of the glial scar.A very slow rate of proliferation can be indicative for a stem cell in certain tissues and is widely considered as a primary step leading towards their identification. We devised a method that combined postembedding, detection and ultrastructural characterization of immunogold labeled cells, thus allowing for the relatively rapid screening of rarely dividing cells in the adult central nervous system. This technique was applied to identify the ultrastructure of slowly proliferating putative stern cells in the adult mouse spinal cord.A specific supplement added to the culture medium was shown to have a selective effect on the propagation of distinct neural stem cell populations, This was in contrast to hypoxic culture conditions which were shown not to have this specific effect on neural stem cell propagation. There were no apparent differences between the distinct neural stem cell populations in their morphology, capacity for self-renewal, or ability to differentiate into glia and neurons. Intraventricular infusion of EphB2 receptor leads to a cellular rearrangement in the subventricular zone with astrocytes contacting the ventricular lumen. After infusing EphB2 receptors or vehicle solution, an upregulation of GFAP expression in ependymal cells was seen in both cases. We conclude that this is an injury related reaction rather than a specific effect of EphB2.The adult mammalian hippocampus and olfactory bulb are structures with an extensive, continuous generation of interneurons derived from stem cells. We asked whether there may also be a turnover of neurons in other regions of the adult brain, and focused on the substantia nigra pars compacta in the midbrain, where the dopamine- producing neurons that are lost in Parkinson's disease reside. We found that despite ongoing neuronal cell death in the substantia nigra, total cell number remained constant over a large part of the life span of the adult mouse. This indicated that there must be the generation of new neurons to compensate for cell loss. After long term labeling with either BrdU or DiI, we found TH-positive neurons with BrdU positive nuclei or DiI labeled membranes were found. We obtained similar results after labeling with tritiated thymidine followed by autoradiography. As the most likely origin for newborn dopaminergic neurons, we identified ependymal cells lining the third ventricular recess and the cerebral aqueduct by labeling with BrdU or DiI. Newborn neurons were found to send projections to their target area and integrate into the local synaptic circuitry as assessed by retrograde tracing and pseudorabies virus labeling studies. Similar to other injury studies, we could show that the rate of neurogenesis is increased after selectively ablating dopaminergic neurons with the toxin MPTP.List of scientific papersI. Johansson CB, Momma S, Clarke DL, Risling M, Lendahl U, Frisen J (1999). Identification of a neural stem cell in the adult mammalian central nervous system. Cell. 96(1): 25-34. https://pubmed.ncbi.nlm.nih.gov/9989494II. Momma S, Vasilyeva E, Tomilin N, Shupliakov O (2002). Ultrastructural identification of dividing cells in the adult mammalian central nervous system. J Neurosci Methods. 119(1): 59-63. https://pubmed.ncbi.nlm.nih.gov/12234636III. Momma S, Cassidy R, Holmberg J, Nilsson L, Shupliakov O, Frisen J (2002). A relationship between two neural stem cell populations in the adult mammalian brain. [Manuscript]IV. Zhao M, Momma S, Delfani K, Carlen M, Cassidy R, Brismar H, Johansson CB, Shupliakov O, Frisen J, Janson AM (2002). Neurogenesis in the adult mammalian substantia nigra. [Submitted]</p
Changes to the cerite group nomenclature
No full textThe cerite and merrillite groups belong to the cerite supergroup. Some nomenclature and classification changes have been made to the cerite group, whereas the merrillite group remains unchanged. Minerals of the cerite group have the general formula A9XM[T7O24Ø4]Z3, where T is Si. The cerite group, from now on, is subdivided into two subgroups, cerite and taipingite. The root name will be cerite and taipingite if the Z anions are dominated by (OH) and F, respectively. The prefix ferri-or alumino-will be added if the M cations are dominated by Fe3+ or Al, respectively. If the M cation is Mg, there will be no prefix. Taking into account the valency-imposed double site occupancy and the site total charge approach, a double suffix will be used to represent the essential A constituents in the general chemical formula. Cerite-(Ce), aluminocerite-(Ce), ferricerite-(La), and taipingite-(Ce) have been renamed cerite-(CeCa), aluminocerite-(CeCa), ferricerite-(LaCa), and taipingite-(CeCa), respectively. The newly approved mineral aluminotaipingite-(CeCa) also belongs to the taipingite subgroup
Unaccusativity in Sentence Production
No full text Linguistic analyses suggest that there are two types of intransitive verbs: unaccusatives, whose sole argument is a patient or theme (e.g., fall), and unergatives, whose sole argument is an agent (e.g., jump). 1 Past psycholinguistic experiments suggest that this distinction affects how sentences are processed: for example, it modulates both comprehension processes ( Bever and Sanz 1997 , Friedmann et al. 2008 ) and production processes ( Kegl 1995 , Kim 2006 , M. Lee and Thompson 2004 , J. Lee and Thompson 2011 , McAllister et al. 2009 ). Given this body of evidence, it is reasonable to assume, as we do here, that this distinction is directly relevant to psycholinguistic theorizing. However, especially in production, exactly how this distinction affects processing is unknown, beyond the suggestion that unaccusatives somehow involve more complex processing than unergatives (see J. Lee and Thompson 2011 ). Here we examine how real-time planning processes in production differ for unaccusatives and unergatives. We build on previous studies on lookahead effects in sentence planning that show that verbs are planned before a deep object is uttered but not before a deep subject is uttered ( Momma, Slevc, and Phillips 2015 , 2016 ). (We use terms like deep subject in a theory-neutral fashion, with no intended commitment to a specific syntactic encoding.) This line of research sheds light on the broader issue of how the theory of argument structure relates to sentence production. </jats:p
Crystal structure of thermophilic dextranase from Thermoanaerobacter pseudethanolicus
No full textThe crystal structures of the wild type and catalytic mutant Asp-312→Gly in complex with isomaltohexaose of endo-1,6-dextranase from the thermophilic bacterium Thermoanaerobacter pseudethanolicus (TpDex), belonging to the glycoside hydrolase family 66, were determined. TpDex consists of three structural domains, a catalytic domain comprising an (β/α)8-barrel and two β-domains located at both N- and C-terminal ends. The isomaltohexaose-complex structure demonstrated that the isomaltohexaose molecule was bound across the catalytic site, showing that TpDex had six subsites (-4 to +2) in the catalytic cleft. Marked movement of the Trp-376 side-chain along with loop 6, which was the side wall component of the cleft at subsite +1, was observed to occupy subsite +1, indicating that it might expel the cleaved aglycone subsite after the hydrolysis reaction. Structural comparison with other mesophilic enzymes indicated that several structural features of TpDex, loop deletion, salt bridge and surface-exposed charged residue, may contribute to thermostability.open
"Life is Wonderful, There’s No Doubt About That": (Big and Small) Stories of an Embodied Positive Ageing Identity
No full textThis chapter forms part of a broader research project exploring narratives of the ageing, sporting body (Phoenix and Sparkes, 2006, 2007; Phoenix, Smith and Sparkes, 2007; Phoenix and Sparkes, 2008). Here, I examine the accomplishment of a positive ageing identity through the stories told by a 71 year old male. In order to examine how identity is narratively accomplished, I have found recent debates within narrative research between a “big story” and “small story” approach especially useful (Bamberg, 2006; Freeman, 2006)
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