Biology subjects

Radler, M. R.

Publications and source records attributed to Radler, M. R..

3 recordsLinked to original sources

bioRxiv2022

Pyramidal neuron morphogenesis requires a septin network that stabilizes filopodia and suppresses lamellipodia during neurite initiation

Pyramidal neurons are the major cell type of the forebrain, consisting of a pyramidally shaped soma with axonal and apicobasal dendritic processes. It is poorly understood how the neuronal soma morphs from a sphere to pyramid, while generating neurites of the proper shape and orientation. Here, we discovered that the spherical somata of immature neurite-less neurons possess a circumferential wreath-like network of septin filaments, which promotes myosin II localization and suppresses Arp2/3 activity at the base of filopodial actin bundles. The septin network facilitates neurite formation by stabilizing nascent filopodia, which mature to neurites, and concomitantly maintains a consolidated soma by suppressing the extension of lamellipodia. We show that this septin function is critical for the morphogenesis and spatial orientation of pyramidal somata and their neurites in vitro and in vivo. Therefore, the somatic septin cytoskeleton provides a key morphogenetic mechanism for neuritogenesis and the development of pyramidal neurons. Highlights- A septin wreath-like network controls the shape of neuronal somata and nascent neurites - Septins promote and suppress filopodial and lamellipodial protrusions, respectively - Septins scaffold myosin II and exclude Arp2/3 at the base of filopodial actin - Development of pyramidally shaped neurons requires septins in vitro and in vivo eTOC SummaryRadler et al report a new morphogenetic mechanism in the development of pyramidal neurons, which is mediated by a septin wreath-like cytoskeleton in the soma of immature spherical neurons. The septin network stabilizes somatic filopodia and suppresses lamellipodia by differentially controlling the localization of myosin II and Arp2/3.

cell biology↗

bioRxiv2022

Septins mediate a microtubule-actin crosstalk that enables actin growth on microtubules

Cellular morphogenesis and processes such as cell division and migration require the coordination of the microtubule and actin cytoskeletons (1, 2). Microtubule-actin crosstalk is poorly understood and largely regarded as the capture and regulation of microtubules by actin (1, 2). Septins are filamentous GTP-binding proteins, which comprise the fourth component of the cytoskeleton along microtubules, actin and intermediate filaments (3, 4). Here, we report that septins mediate microtubule-actin crosstalk by coupling actin polymerization to microtubule lattices. Super-resolution imaging shows that septins localize to overlapping microtubules and actin filaments in the growth cones of neurons and non-neuronal cells. We show that recombinant septin complexes directly crosslink microtubules and actin filaments into hybrid bundles. In vitro reconstitution assays reveal that microtubule-bound septins capture and align stable actin filaments with microtubules. Strikingly, septins enable the capture and polymerization of growing actin filaments on microtubule lattices. In neuronal growth cones, septins are required for the maintenance of the peripheral actin network that fans out from microtubules. These findings provide the first evidence of septins directly mediating microtubule interactions with actin filaments, and reveal a new mechanism of microtubule-templated actin growth with broader significance for the self-organization of the cytoskeleton and cellular morphogenesis. Significance StatementCellular morphogenesis and processes such as cell division and cell migration require the coordination of the actin and microtubule cytoskeletons. Despite its broader physiological significance, actin-microtubule crosstalk is molecularly and mechanistically poorly understood. Actin-microtubule crosstalk has been viewed primarily as the regulation or guidance of microtubule dynamics by actin filaments. Here, we have discovered a new mechanism by which actin filament growth is guided by microtubules. We report that septins, a poorly understood component of the cytoskeleton, can capture and link the polymerizing ends of actin filaments to microtubule polymers. We present evidence that this new septin-mediated mechanism is critical for the morphology of growth cones, which are structures that direct the growth of neuronal axons through actin-microtubule crosstalk.

cell biology↗

bioRxiv2019

Septin 2/6/7 complexes tune microtubule plus end growth and EB1 binding in a concentration-dependent manner

Septins are filamentous GTP-binding proteins, which affect microtubule (MT) dependent functions including membrane trafficking and cell division, but their precise role in MT dynamics is poorly understood. Here, in vitro reconstitution of MT dynamics with SEPT2/6/7, the minimal subunits of septin heteromers, shows that SEPT2/6/7 has a biphasic concentration-dependent effect on MT growth. Lower concentrations of SEPT2/6/7 enhance MT plus end growth and elongation, while higher and intermediate concentrations inhibit and pause plus end growth, respectively. We show that SEPT2/6/7 has a 1.5-fold preference for GTP-over GDP-bound MT lattice, and competes with EB1 for binding to GTP{gamma}S-stabilized MTs, which mimic the EB1-preferred GDP-Pi state of polymerized tubulin. Strikingly, SEPT2/6/7 triggers EB1 dissociation from plus end tips in cis by binding to the MT lattice and in trans when MT plus ends collide with SEPT2/6/7 filaments. At these intersections, SEPT2/6/7 filaments were more potent barriers than actin filaments in pausing MT growth and dissociating EB1 in vitro and in live cells. These data demonstrate that SEPT2/6/7 complexes and filaments can directly impact MT plus end growth and the tracking of plus end-binding proteins, and thereby may facilitate the capture of MT plus ends at intracellular sites of septin enrichment.\n\nHighlight Summary for eTOCKnowledge of septin roles in MT dynamics is poor and confounded by knockdown studies. Here, in vitro reconstitution assays show concentration-dependent effects of SEPT2/6/7 on MT plus end growth, pausing and EB1 tracking. We found that SEPT2/6/7 filaments are potent than actin in pausing MT growth and dissociating EB1 from intersecting plus ends.

cell biology↗