Radial somatic F‐actin organization affects growth cone dynamics during early neuronal development

Abstract

The centrosome is thought to be the major neuronal microtubule‐organizing center (MTOC) in early neuronal development, producing microtubules with a radial organization. In addition, albeit in vitro, recent work showed that isolated centrosomes could serve as an actin‐organizing center, raising the possibility that neuronal development may, in addition, require a centrosome‐based actin radial organization. Here, we report, using super‐resolution microscopy and live‐cell imaging of cultured rodent neurons, F‐actin organization around the centrosome with dynamic F‐actin aster‐like structures with F‐actin fibers extending and retracting actively. Photoactivation/photoconversion experiments and molecular manipulations of F‐actin stability reveal a robust flux of somatic F‐actin toward the cell periphery. Finally, we show that somatic F‐actin intermingles with centrosomal PCM‐1 (pericentriolar material 1 protein) satellites. Knockdown of PCM‐1 and disruption of centrosomal activity not only affect F‐actin dynamics near the centrosome but also in distal growth cones. Collectively, the data show a radial F‐actin organization during early neuronal development, which might be a cellular mechanism for providing peripheral regions with a fast and continuous source of actin polymers, hence sustaining initial neuronal development.

Emerging roles of the centrosome in neuronal development

“…The F-actin in the soma of neurons appeared as dynamic aster-like structures, closely associated with PCM-1 satellites (Figure 3). Furthermore, with Live-STED (stimulated emission depletion) microscopy, we discovered constant extensions of F-actin fibers from these dynamic F-actin asters (Meka et al, 2019). Interestingly, the F-actin asters in the soma of developing neurons (Meka et al, 2019) and the so-called actin hotspots in axon shafts of more matured neurons (Chakrabarty et al, 2019;Ganguly et al, 2015) are Formin but not Arp2/3-dependent.…”

“…Furthermore, with Live-STED (stimulated emission depletion) microscopy, we discovered constant extensions of F-actin fibers from these dynamic F-actin asters (Meka et al, 2019). Interestingly, the F-actin asters in the soma of developing neurons (Meka et al, 2019) and the so-called actin hotspots in axon shafts of more matured neurons (Chakrabarty et al, 2019;Ganguly et al, 2015) are Formin but not Arp2/3-dependent. Using a photoactivatable F-actin probe, PaGFP-UtrCH, (Burkel, Bement, & Labs, 2015), we were able to show an anterograde F-actin movement from the soma to the growth cones/neurite tips.…”

“…Using a photoactivatable F-actin probe, PaGFP-UtrCH, (Burkel, Bement, & Labs, 2015), we were able to show an anterograde F-actin movement from the soma to the growth cones/neurite tips. Photoactivation of PCM-1 Knockdown (Meka et al, 2019) Centrosome ( F I G U R E 3 Illustration of the radial somatic F-actin organization in a developing neuron and how it is affected upon on PCM-1 knockdown and its implications in neuronal polarization (a hypothetical idea). F-actin organized around the centrosome is a source of peripheral F-actin, which helps to modulate growth cone dynamics (Meka et al, 2019).…”

“…Photoactivation of PCM-1 Knockdown (Meka et al, 2019) Centrosome ( F I G U R E 3 Illustration of the radial somatic F-actin organization in a developing neuron and how it is affected upon on PCM-1 knockdown and its implications in neuronal polarization (a hypothetical idea). F-actin organized around the centrosome is a source of peripheral F-actin, which helps to modulate growth cone dynamics (Meka et al, 2019). PCM-1 knockdown (that affects PCM protein recruitment and disturbs radial MTOC organization-discussed in the introduction section) results in the reduction of somatic F-actin asters and promotes neurite elongation due to decreased F-actin delivery to the periphery (left side).…”

“…It is suggested that the centrosome gradually loses its ability to radially organize microtubules after axons specification in cultured primary neurons (Stiess et al, 2010). Additionally, recent studies show that the centrosome can organize the actin cytoskeleton during lymphocyte polarity (Obino et al, 2016), cell division (Plessner, Knerr, & Grosse, 2019), and neuronal development (Meka et al, 2019). This review is intended to summarize the data regarding the role of the centrosome during axon specification and neuronal migration with special focus on recent discoveries, which suggest the centrosome as an F-actin cytoskeleton regulator during neuronal differentiation.…”