Dynamics of Centrosome Translocation and Microtubule Organization in Neocortical Neurons during Distinct Modes of Polarization

Abstract

Neuronal migration and process formation require cytoskeletal organization and remodeling. Recent studies suggest that centrosome translocation is involved in initial axon outgrowth, while the role of centrosomal positioning is not clear. Here, we examine relations between centrosomal positioning, axonogenesis, and microtubule (MT) polarization in multipolar and bipolar neocortical neurons. We monitored dynamic movements of centrosomes and MT plus ends in migratory neurons in embryonic mouse cerebral slices. In locomoting bipolar neurons, the centrosome oriented toward the pia-directed leading process. Bipolar neurons displayed dense MT plus end dynamics in leading processes, while trailing processes showed clear bidirectional MTs. In migrating multipolar neurons, new processes emerged irrespective of centrosome localization, followed by centrosome reorientations toward the dominant process. Anterograde movements of MT plus ends occurred in growing processes and retrograde movements were observed after retraction of the distal tip. In multipolar neurons, axon formed by tangential extension of a dominant process and the centrosome oriented toward the growing axon, while in locomoting neurons, an axon formed opposite to the direction of migration and the centrosome localized to the base of the leading process. Our data suggest that MT organization may alter centrosomal localization and that centrosomal positioning does not necessarily direct process formation.

Distinct temporal hierarchies in membrane and cytoskeleton dynamics precede the morphological polarization of developing neurons

“…The position of the second neurite is fixed at the opposite pole (de Anda et al, 2008;Menchón et al, 2011) by mechanisms that are still poorly characterized. This bipolar architecture supports migration (Hatanaka and Murakami, 2002;Sakakibara et al, 2014), as well as subsequent axonal and dendritic growth (Noctor et al, 2004), and thus influences the final organization of the entire brain.…”

“…4), does not mark the future axon. Taking into account that MT dynamics is polarized in neurons in vitro during (and just shortly before) axon outgrowth, and that actin dynamics is polarized in neurons with several neurites and during neuronal migration (Bradke and Dotti, 1999;Sakakibara et al, 2014;Solecki et al, 2009;Witte et al, 2008) our new results suggest that polarized actin and MT dynamics, albeit present in the earliest stages, do not contribute to the polarity 'memory' at the bipolar stage, even though one of the two neurites is in the process of becoming distinct from the other, in morphology and dynamics. Interestingly, we found that membrane turnover, in terms of both exocytosis and endocytosis, is asymmetrically distributed in bipolar cells (Fig.…”

“…In the future, it will be interesting to combine the analysis of intracellular organization using tagged marker proteins with long-term timelapse imaging in order to unravel changes in intracellular organization throughout all developmental stages in vivo. In vivo, it has been shown that excitatory cortical neurons form their axon either during their multipolar stage (de Anda et al, 2010;Hatanaka and Yamauchi, 2013;Namba et al, 2014;Sakakibara et al, 2014) or during their bipolar migrating phase (Noctor et al, 2004;Sakakibara et al, 2014). It thus seems that neurons can establish axonal polarity at different times, perhaps depending on their origin.…”

“…In fact, Tabata and colleagues (Tabata et al, 2009) have shown that the migratory behaviour of neurons derived from either radial glia progenitors or intermediate progenitors differ. Interestingly, centrosome position in vivo is correlated with the future axon (Andersen and Halloran, 2012;de Anda et al, 2010) or with the 'dominant' process (Sakakibara et al, 2014) in neurons that form their axon during the multipolar stage. By contrast, in bipolar neurons, the axon forms on the opposite side of the centrosome, which is located at the base of the leading neurite (Sakakibara et al, 2014).…”

Reelin and cofilin cooperate during the migration of cortical neurons: A quantitative morphological analysis

“…Cofilin S3A is likely to produce many free barbed F-actin ends, which might initiate the branching activity of the Arp2/3 complex (Svitkina and Borisy, 1999;Pantaloni et al, 2000;Volkmann et al, 2001;Amann and Pollard, 2001;Ichetovkin et al, 2002). Ongoing reorganization of the actin cytoskeleton in S3A neurons might not only lead to the formation of supernumerary processes but might also result in remodeling of microtubules as well as altered localization of the centrosome (Solecki et al, 2009;Sakakibara et al, 2014), which determines neuronal polarity (de Anda et al, 2005). As a consequence, the cells will change migration direction.…”