Abstract
Under certain circumstances differentiated cells can be reprogrammed to form stem cells in land plants, but only a portion of the cells reprograms successfully. A long-distance inhibitory signal from reprogrammed cells to surrounding cells has been reported in some ferns. Here we show the existence of anisotropic inhibitory signal to regulate stem cell formation in the moss Physcomitrella patens. When single cells were isolated from a gametophore leaf, over 90% of them were reprogrammed to stem cells with characteristic nuclear expansion. By contrast, when two adjacent cells were isolated, the nuclei of both cells expanded, but successful reprogramming of both cells occurred only in approximately one fifth of the pairs. When three aligned cells were isolated, the reprogramming rate of both edge cells decreased with a living middle cell but did not with a dead middle cell. Furthermore, unequal conversion into stem cells was more prominent in cell pairs aligned parallel to the proximal-distal leaf axis than in those perpendicular to the axis. This study gives an insight into the role of the inhibitory signal in development and evolution as well as the efficient stem cell induction from differentiated cells.
Highlights
During development, both plants and animals form stem cells, which can self-renew and produce differentiated cells to generate the body[1, 2]
When we isolated individual single leaf cells by hand using a carbon knife to remove the debris as much as possible, the isolated cell acquired tip-growth and reentered into the cell cycle, indicating that single isolated leaf cells are autonomously reprogrammed to cells that are similar to chloronema apical stem cells (Fig. 1a, Supplementary Video 1)
Since nuclear size expansion is associated with reprogramming in metazoans[15, 16] and we preliminarily observed that the nuclear size of chloronema apical stem cells is larger than that of gametophore leaf cells, we developed a system to measure the size of the nucleus in each isolated cell to examine whether the nuclear size of leaf cells becomes larger before the cell division
Summary
Both plants and animals form stem cells, which can self-renew and produce differentiated cells to generate the body[1, 2]. Two stem cells were formed in approximately 10% of these experiments, cases proposed to represent occurrences of two cells simultaneously reprogramming to stem cells[10] These findings suggest that stem cells produce an inhibitory signal that is rapidly and efficiently transmitted to surrounding cells[11]. In the model moss Physcomitrella patens (Physcomitrella), multiple differentiated leaf cells facing a cut are reprogrammed to become putative chloronema apical stem cells within 48 h after dissection, without application of exogenous phytohormones[14] These differences suggest that the regulatory mechanisms of stem cell formation from differentiated cells in Physcomitrella are distinct from those in ferns. We examined the spatial effects of the inhibitory signal by isolating groups of three aligned cells From these findings we propose that an inhibitory signal for stem cell formation is produced by cells undergoing reprogramming and that this cell fate-dependent signal is anisotropically transmitted
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