Microtubule Associated Protein 1 b (Map1b) is required for neurulation in zebrafish
Creators: name: Nemani, Neeharika
Publisher: name: Maryland Shared Open Access Repository
Year: 2011
Subjects: Microtubule associated proteins
Microtubules
Neural convergence
Neurulation

description: The neural tube (the precursor of the brain and spinal cord) is shaped during neurulation from a flat sheet of cells on the dorsal surface of the embryo known as the neural plate. Neural convergence, an early stage of neurulation that is conserved across vertebrates, results in the narrowing and elongation of the neural plate. In zebrafish, this morphogenetic process is brought about by polarized cell movements within the neural plate directed towards the dorsal midline. Research in our laboratory focuses on understanding the role of microtubules (MTs) during neural convergence and the identification of pathways implicated in MT stabilization. Firstly, the stability of MTs increases as neurulation proceeds, as visualized using a marker for detyrosinated MTs. In addition, MTs are destabilized in linguini mutants, which are defective in neural convergence (but not convergence of the underlying mesodermal layer). The lack of mesodermal defects in these mutants further indicates that there are mechanisms in place to stabilize MTs in the neural ectoderm specifically. Based on these observations, we predict that microtubule associated proteins (MAPs) are likely to function as downstream signaling molecules to stabilize MTs during neural convergence. We report here on the role of Map1b during neurulation. Map1b is a developmentally regulated phosphoprotein that is predominantly expressed in nerve cells. It is one of the first structural MAPs to be expressed at high levels in growing axons and growth cones. Map1b mouse knockout studies have revealed a significant role for this protein during central nervous system development. However, a role for this protein in neurulation has not been investigated.To address whether Map1b is required for neural convergence, we first examined its expression using whole mount in situ hybridization. This study revealed ubiquitous expression of Map1b at the neural plate (tailbud) stage and continuing into later stages of neural tube development. In the newly formed neural tube Map1b expression became more concentrated in the hindbrain region. Thus, Map1b expression is consistent with a potential role for this molecule in neural convergence. To address whether Map1b is required for neural convergence we analyzed dlx3 (a marker for the edge of the neural plate) expression in embryos in which this protein was depleted using morpholinos. This assay revealed that the width of the neural plate was 1.5 times wider in the Map1b morpholino-injected as compared to control, uninjected, embryos. Since it is known that MTs are required for cell elongation during neural convergence, we measured the length-width ratio (LWR) of the cells in Map1b-depleted and control embryos. The quantification data revealed a 1.8 times increased LWR of cells in the control embryo as compared to Map1b MO-injected embryos. These findings suggest that Map1b mediates the polarization and elongation of cells during neural convergence by regulating MT stability, thus revealing a novel role for Map1b in regulating the morphogenetic movements that shape the vertebrate nervous system.