Estudio de la función de la proteína asociada a microtúbulos 1B durante el desarrollo neuronal

Abstract

XVMAP1B is a microtubule-associated protein that was discovered as a protein which main role is to promote tubulin assembly and to stabilize microtubules (MTs). MAP1B has also been shown to bind actin and to regulate a population of dynamic MTs. MAP1B is expressed prominently during early stages of neuronal development and it has been implicated in axonal growth, neuronal migration and axonal guidance. However, MAP1B is still expressed in adult brain areas with high synaptic plasticity with an unknown function. In this work we have studied the role of MAP1B in the regulation of MTs and actin dynamics, and its implication during neuronal developmental stages as axonal elongation and dendritic spines formation and maturation. Here we have shown that MAP1B participates in regulating MT dynamics. Our results indicate that, in the absence of MAP1B, MTs nucleate less and faster. Moreover, we have presented that MAP1B regulates the binding of some +TIPs to MTs and, in some cases, their protein level. Moreover, it co-immunoprecipitates with some +TIPs with CAP-Gly domains and with a brain-enriched EB protein, EB3. This suggests that MAP1B could form a complex with these +TIPs and regulate their behavior thereby contributing to the modulation of MT dynamic. Moreover, we have presented evidences that MAP1B regulates Rho-GTPases activity by binding the Rac1-GEF Tiam1 and the RhoA-GEF GEF-H1. This binding takes place during early neuronal development and in adult stages. In this way, neurons lacking MAP1B show a decrease in Rac1 and cdc42 activity, and an increase in RhoA activity. According with this, in the absence of MAP1B the phosphorylation levels of some proteins activated by these Rho- GTPases are altered. This alteration in Rho-GTPases activity could explain the diminution in axonal elongation. In mature neurons, we have provided evidences that MAP1B is present in some dendritic spines in which development it is implicated. In agreement with this, neurons obtained from MAP1B-deficient mice show a decrease in density of mature dendritic spines and an increase of immature filopodia-like protrusions. Although these neurons show normal passive membrane properties, action potential properties and firing rates, we didn`t observed any LTP-induction. The morphological alterations observed in dendritic protrusion in neurons lacking MAP1B could be explained by the Rho-GTPases alterations described previously. Taken together, these results define a new and important function of MAP1B in the regulation of actin and tubulin cytoskeleton dynamics during neuronal development and maturation.