Lamellipodia (ruffles): Sheet-like cellular actin-containing cellular protrusions. Junctional exchange: Cellular partner rearrangements, such as those seen during convergent extension of epithelial intercalation, in which existing cell junctions are replaced by novel junctions with different cells. Interkinetic nuclear migration (IKNM): The movement of nuclei along the apicobasal axis, depending on the cell cycle in a pseudostratified epithelium. Holoprosencephaly: Severe brain defect resulting from failure of the forebrain to divide into bilateral hemispheres. Neurulation in teleost fish has been likened to secondary neurulation in higher vertebrates.Īnencephaly: Absence of brain and skull vault due to neural tissue degeneration following failed cranial neural tube closure.Īpical constriction: Contraction of the apical side of a cell.Ĭlosure 1: The initial neural tube closure event at the hindbrain/cervical boundary in mice.Ĭonvergent extension (CE): The process by which a tissue narrows along its mediolateral axis (convergence) and elongates along its anteroposterior/rostrocaudal axis (extension).Ĭraniorachischisis: An open neural tube defect involving the midbrain, hindbrain and entire spinal cord.Įxencephaly: Failure of neural tube closure in the developing brain the precursor of anencephaly.įilopodia: Spike-like cellular actin-containing cellular protrusions. In this process, a solid cord of NT progenitor cells in the developing tail bud becomes ‘canalized’ to form a neuroepithelium (NE) surrounding a lumen, without formation or closure of neural folds ( Copp et al., 2015). 1 see Glossary, Box 1) in an apparently similar manner. Although mammals, birds and amphibians have differences in primary neurulation all undergo ‘secondary’ neurulation ( Fig. For example, there is also a sequence of neurulation events along the body axis that involves multi-site, progressive closure (‘zippering’) in mammals, a somewhat simpler sequence of closure events in birds, and almost simultaneous closure at all axial levels in amphibia ( Fig. However, primary neurulation varies between species (see Box 2). 1): the NP is initially induced to differentiate, it then undergoes bending to create the neural folds, which elevate towards the dorsal midline, and finally the neural fold tips fuse to complete the NT. Primary neurulation (see Glossary, Box 1) – the process by which the NT closes from an open neural plate (NP) – is achieved sequentially in distinct steps ( Fig. Vertebrate neurulation is a complex morphogenetic process that requires the coordination of many cellular and molecular events, and is regulated by more than 300 genes in mammals ( Wilde et al., 2014). How the neural tube (NT) forms is a central issue in developmental biology.
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