Analysis of Myosin XI Localization During Cell Division in Physcomitrella patens

Sun, Hao

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Analysis of Myosin XI Localization During Cell Division in Physcomitrella patens

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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.

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