CAMSAPs organize an acentrosomal microtubule network from basal varicosities in radial glial cells
A high number of genetic mutations associated with cortical malformations are found in genes coding for microtubule-related factors. Accordingly, microtubules play a variety of functions in RG cells, including cell division and polarized transport. A large number of microtubule regulators linked to disease have been studies in the past but surprisingly, the organization of the microtubule cytoskeleton I these cells remained unknown. This was mostly due to the challenge of performing subcellular live imaging within this thick tissue. We therefore developed a reliable method to perform high speed and high-resolution live imaging within brain slices, which we have been using for several studies. Using the method, we indentified the organization of the microtubule cytoskeleton in RG cells (Coquand et al, JCB, 2021). We showed that microtubules in the apical process uniformly emanate from the pericentrosomal region, while microtubules in the basal fiber display a mixed polarity, reminiscent of the mammalian dendrite. We identified acentrosomal microtubule organizing centers localized in varicosities of the basal fiber and showed that CAMSAP family members accumulate in these varicosities where they control microtubule growth. Double knockdown of CAMSAP1 & 2 led to a destabilization of the entire basal process. Finally, using live imaging of human fetal cortex, we revealed that this organization is conserved in basal radial glial cells, the progenitor cell population associated with human brain size expansion.
Microtubule organization in aRG and bRG cells.
(Left) Live imaging of CAMSAP3-GFP and EB3-mCherry in mouse aRG cell basal process, and corresponding kymograph.
(Right) The microtubule network of the apical process of aRG cells is unipolar, with the minus ends concentrated apically, and the plus ends growing in the basal direction. The mother centriole serves as a template for the primary cilium, which extends into the ventricle. A second ring-like microtubule network is present at the apical endfoot (PMID: 32238932). In the basal process of both aRG and bRG cells, the microtubule network in bipolar. Microtubules are organized from varicosities, via CAMSAP 1 & 2, which anchor the minus ends.
Coquand L.*, Victoria G. S.*, Tata A., Brault J.B., Guimiot F., Fraisier V., Baffet AD (2021) CAMSAPs organize an acentrosomal microtubule network from basal varicosities in radial glial cells. J Cell Biol. 2;220(8):e202003151