Abstract
BackgroundMorphogenesis requires developmental processes to occur both at the right time and in the right place. During neural tube formation in the zebrafish embryo, the generation of the apical specializations of the lumen must occur in the center of the neural rod after the neural cells have undergone convergence, invagination and interdigitation across the midline. How this coordination is achieved is uncertain. One possibility is that environmental signaling at the midline of the neural rod controls the schedule of apical polarization. Alternatively, polarization could be regulated by a timing mechanism and then independent morphogenetic processes ensure the cells are in the correct spatial location.ResultsEctopic transplantation demonstrates the local environment of the neural midline is not required for neural cell polarization. Neural cells can self-organize into epithelial cysts in ectopic locations in the embryo and also in three-dimensional gel cultures. Heterochronic transplants demonstrate that the schedule of polarization and the specialized cell divisions characteristic of the neural rod are more strongly regulated by time than local environmental signals. The cells’ schedule for polarization is set prior to gastrulation, is stable through several rounds of cell division and appears independent of the morphogenetic movements of gastrulation and neurulation.ConclusionsTime rather than local environment regulates the schedule of epithelial polarization in zebrafish neural rod.
Highlights
Morphogenesis requires developmental processes to occur both at the right time and in the right place
Immunohistochemistry revealed that zonula occludens 1 (ZO-1) was localized to the center of the cluster indicating the presence of apical epithelial junctions, and the extracellular matrix component laminin surrounded the cluster at the cells’ basal surface (Figure 1F)
The arrangement and polarity of cells within the cluster is similar to the structure of the neural tube and suggests that in these ectopic locations, the cluster of neural cells polarize and assemble a neuroepithelium that surrounds a central lumen
Summary
Morphogenesis requires developmental processes to occur both at the right time and in the right place. During neural tube formation in the zebrafish embryo, the generation of the apical specializations of the lumen must occur in the center of the neural rod after the neural cells have undergone convergence, invagination and interdigitation across the midline How this coordination is achieved is uncertain. The emergence of neuroepithelial polarity is a critical step in this process that determines a distinct transition in cell behavior Prior to this point, stable cell-cell junctions do not appear to be present within the core of the neural keel and this allows cells to undergo considerable rearrangements, including cell division and intercalation of cells across the midline of the keel and rod [11,12]. After epithelialization and lumen assembly, exchange of cells across the midline is not possible and a more stable epithelial structure is maintained by junctional belts that lie at the interface of apical and basolateral membrane domains and tether cells to their neighbors
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