Abstract
Specialization of the cell-division process is a common feature of developing embryos, but most studies on vertebrate cell division have focused on cells dividing in culture. Here, we used in vivo four-dimensional confocal microscopy to explore the role of Cdc42 in governing cell division in the developing neural epithelium of Xenopus laevis. We find that Cdc42 is crucial for stable positioning of the metaphase spindle in these cells, but was not required for spindle positioning in epidermal epithelial cells. We also find that divisions in the Xenopus neural plate are planar oriented, and that rotations of mitotic spindles are essential for establishing this orientation. When Cdc42 is disrupted, spindles over-rotate and the final orientation of divisions is changed. Finally, the planar orientation of cell divisions in this tissue seems to be independent of planar cell polarity (PCP) signaling and does not require normal neural morphogenesis. Our data provide new insights into the coordination of cell division and morphogenesis in epithelial cell sheets and reveal novel, cell-type-specific roles for Cdc42 in spindle positioning and spindle orientation.
Highlights
Regulated cell division is a central facet of embryogenesis, and how cells establish orientation and asymmetries during cell division is a fundamental issue at the interface of cell and developmental biology
We show here that manipulation of Cdc42 in neural epithelial cells during neural tube closure results in a failure of cells to stabilize the mitotic spindle in the cell center during metaphase
In vivo imaging of cell division and mosaic analysis of gene function during Xenopus neural tube closure We have developed a method to examine cell divisions using threedimensional (3D) time-lapse confocal microscopy in intact, developing vertebrate embryos during neural tube closure. mRNAs encoding fluorescent fusion proteins were injected into the early blastomeres of Xenopus embryos, typically at the four-cell stage (Fig. 1A, 1)
Summary
Regulated cell division is a central facet of embryogenesis, and how cells establish orientation and asymmetries during cell division is a fundamental issue at the interface of cell and developmental biology. During neural tube closure in chick embryos, the axis of cell division is preferentially parallel to the long axis of the embryo (Sausedo et al, 1997), whereas, in zebrafish, divisions are initially parallel to the long axis and shift to a perpendicular orientation as neurulation proceeds (Concha and Adams, 1998; Geldmacher-Voss et al, 2003; Gong et al, 2004). The neural plate of Xenopus has two cell layers, a deep layer giving rise to the primary neurons and a superficial layer that only differentiates much later and continues to proliferate dramatically during neural tube closure (Chalmers et al, 2002; Hartenstein, 1989)
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