Cell division is an important biological process, thus it is always an active field in biological research. To complete cell division, plant cells form a new cell wall that separates the two new cells. In contrast to the contractile ring of animal cells, plant cells form the new cell wall from their interior. Vesicles containing the new cell wall fuse at the cell plate between the two cells. The formation of the cell plate is guided by the phragmoplast, a microtubule and filamentous actin-containing structure. Because vesicles are known to be transported by myosin motors during interphase and little is known about the role of myosin XI during cell division, I investigated the participation of the plant specific myosin XI in cell division. For this work I used the moss Physcomitrella patens as a model organisms because of its simple cytology and powerful genetics. Using a fluorescent protein fusion of myosin XI, I found that this molecule associates with the mitotic spindle immediately after nuclear envelope breakdown. Myosin XI stays associated with the spindle during mitosis, and when the phragmoplast is formed, it concentrates at the cell plate, forming a fine line. Using an actin polymerization inhibitor, latrunculin B, I found that the associations of myosin XI with the mitotic spindle and the phragmoplast are independent of the presence of filamentous actin. After using double-labeled lines for myosin XI the endoplasmic reticulum and vesicle markers, I found the myosin XI on the spindle is not colocalized with the endoplasmic reticulum and two types of vesicle markers. Furthermore, I also found the vesicle trafficking inhibitor, brefeldin A, does not inhibit the localization of myosin XI at the mitotic spindle and the phragmoplast. These observations suggest a new actin-independent behavior of myosin XI during cell division, and provide novel insights to our understanding of the function of myosin XI during plant cell division.

L’allogreffe de cellules souches hématopoïétiques allogéniques (HSCT, hematopoietic stem cell transplantation) reste le seul traitement curatif pour de nombreux patients atteints d’hémopathies malignes. Dans près d’un cas sur deux, l’allogreffe se complique de réaction chronique du greffon contre l'hôte (GVH (graft-versus-host) chronique). Les lymphocytes B régulateurs sont une population de lymphocytes B sécrétant de l’interleukine (IL)-10 et capables d’inhiber les réactions inflammatoires. Nous avons montré que chez l’homme atteint de GVH chronique active, la fréquence des lymphocytes B régulateurs est diminuée dans le sang périphérique. Les lymphocytes B régulateurs sont principalement enrichis dans la population B de phénotype mémoire et plasmablastique. Une augmentation de la fréquence des plasmablastes et une diminution du nombre de lymphocytes B de phénotype mémoire chez les patients allogreffés atteints de GVH chronique active suggèrent des altérations de la différenciation terminale des lymphocytes B. Nos travaux ont également porté sur les lymphocytes NK qui ont un rôle cytotoxique. Nous avons identifié l’un des récepteurs de surface des lymphocytes NK, CD245, comme étant la myosine 18A. La myosine 18A est impliquée dans l’organisation du cytosquelette et constitue un récepteur du surfactant A. Nous avons montre qu’il s’agissait d’un récepteur co-activateur de la cytotoxicité NK et que cette augmentation de cytotoxicité pourrait être liée à la stimulation de l’expression de la molécule de stimulation CD137 (4-1BB) à la surface du lymphocyte NK. Ces résultats suggèrent un potentiel rôle thérapeutique de l’utilisation d’anticorps agonistes spécifiques de CD245. / Allogeneic hematopoietic stem cell transplantation (HSCT) remains the only curative treatment for many patients with haematological malignancies. In almost half of the cases, it is complicated by chronic graft-versus-host disease (cGVHD). Regulatory B cells are a population of B cells secreting interleukin (IL)-10 that can inhibit the immune responses. We have shown that in patients with active cGVHD, the frequency of regulatory B cells is decreased in the peripheral blood. Regulatory B cells are enriched in the memory B cell and plasmablast B cell pools. Increased plasmablasts frequencies and decreased memory B cells frequencies were found in patients with active cGVHD, suggesting alterations in the terminal differentiation of B cells. Our work also focused on NK cells that have a cytotoxic role. We identified one surface receptor of NK cells, CD245, as myosin 18A. Myosin 18A is involved in the organization of the cytoskeleton and is a receptor of the surfactant A. We have shown that myosin 18A was a coactivating receptor of the NK cytotoxicity and that this increase in cytotoxicity could be linked to the stimulation of the expression of CD137 (4-1BB) on the surface of the NK lymphocyte. These results suggest a potential therapeutic role of the use of specific CD245 agonist antibodies.

Longitudinale Untersuchungen der kardialen Morphologie von knockin-Mäusen mit humanen Myosinmutationen / Longitudinal analyses of cardiac morphology in knockin mice carrying human myosin mutations

Primary spinal cord injury (SCI) results from direct mechanical damage to the spinal cord. The resulting pathochemical and pathophysiological events, including oxidative stress and inflammation, lead to secondary injury. The ability to decrease secondary injury may lead to improved recovery. Increasing glutathione production after SCI leads to decreased secondary injury. Glutamine is an important precursor to glutathione following trauma. Skeletal muscle phenotype is strongly influenced by neuromuscular activity. SCI causes myosin heavy chain (MyHC) profiles to shift towards faster isoforms in slow muscles and slower isoforms in fast muscles. The hypothesis was that glutamine, as a precursor of glutathione, administration to SCI rats would lead to better functional recovery and a more preserved MyHC phenotype in locomotory muscles. <p> Rats were assigned to one of four groups; healthy, laminectomy only, untreated SCI, and SCI treated with an intraperitoneal injection of 1mmol/kg glutamine every 12 hours for one week after injury. SCIs were performed at T6 with a modified aneurism clip. Functional recovery was measured weekly using the Basso-Beattie-Bresnahan scale and the angle board method. Six weeks later, all rats were killed, and their extensor digitorum longus and soleus muscles excised and weighed. MyHC composition of the muscles was determined using SDS-PAGE.<p>The hypothesis that glutamine treatment following SCI would lead to better functional recovery and a more preserved MyHC profile was validated. Glutamine treated rats received significantly higher BBB scores (p<0.01) and angle board scores (p<0.001) than untreated SCI rats. Glutamine treatment also reduces muscle atrophy in the soleus muscle, but not the extensor digitorum longus (EDL). In untreated rats the soleus muscle accounted for significantly (p<0.001) less of the percentage of total body weight than the soleus muscle from glutamine treated rats. Finally, SCI rats with preserved functional abilities displayed a significantly better preserved MyHC profile compared to untreated SCI rats. In the soleus healthy rats contain 94% type 1 myosin, treated rats maintained 68% which was significantly (p<0.001) greater than 28% maintained by untreated rats. In the EDL healthy rats contain 55% type 2b myosin, treated rats maintained 32% which was greater than 26% type 2b myosin maintained by untreated rats.

Primary spinal cord injury (SCI) results from direct mechanical damage to the spinal cord. The resulting pathochemical and pathophysiological events, including oxidative stress and inflammation, lead to secondary injury. The ability to decrease secondary injury may lead to improved recovery. Increasing glutathione production after SCI leads to decreased secondary injury. Glutamine is an important precursor to glutathione following trauma. Skeletal muscle phenotype is strongly influenced by neuromuscular activity. SCI causes myosin heavy chain (MyHC) profiles to shift towards faster isoforms in slow muscles and slower isoforms in fast muscles. The hypothesis was that glutamine, as a precursor of glutathione, administration to SCI rats would lead to better functional recovery and a more preserved MyHC phenotype in locomotory muscles. <p> Rats were assigned to one of four groups; healthy, laminectomy only, untreated SCI, and SCI treated with an intraperitoneal injection of 1mmol/kg glutamine every 12 hours for one week after injury. SCIs were performed at T6 with a modified aneurism clip. Functional recovery was measured weekly using the Basso-Beattie-Bresnahan scale and the angle board method. Six weeks later, all rats were killed, and their extensor digitorum longus and soleus muscles excised and weighed. MyHC composition of the muscles was determined using SDS-PAGE.<p>The hypothesis that glutamine treatment following SCI would lead to better functional recovery and a more preserved MyHC profile was validated. Glutamine treated rats received significantly higher BBB scores (p<0.01) and angle board scores (p<0.001) than untreated SCI rats. Glutamine treatment also reduces muscle atrophy in the soleus muscle, but not the extensor digitorum longus (EDL). In untreated rats the soleus muscle accounted for significantly (p<0.001) less of the percentage of total body weight than the soleus muscle from glutamine treated rats. Finally, SCI rats with preserved functional abilities displayed a significantly better preserved MyHC profile compared to untreated SCI rats. In the soleus healthy rats contain 94% type 1 myosin, treated rats maintained 68% which was significantly (p<0.001) greater than 28% maintained by untreated rats. In the EDL healthy rats contain 55% type 2b myosin, treated rats maintained 32% which was greater than 26% type 2b myosin maintained by untreated rats.

Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains ix, 115 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 103-105).

Thesis (Ph. D.)--University of California, San Diego, and San Diego State University, 2004. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Florida State University, 2003. / Advisor: Dr. Tim Logan, Florida State University, College of Arts and Sciences, Program in Molecular Biophysics. Title and description from dissertation home page (viewed Oct. 3, 2003). Includes bibliographical references.

No description available.

published_or_final_version / Biochemistry / Master / Master of Philosophy