Data for: Doublecortin reinforces microtubules to promote growth cone advance in soft environments

Doublecortin (DCX) is a microtubule (MT)-associated protein in immature
neurons. DCX is essential for early brain development, and DCX mutations
account for nearly a quarter of all cases of lissencephaly-spectrum brain
malformations that arise from a neuronal migration failure through the
developing cortex. By analyzing pathogenic DCX missense mutations in
non-neuronal cells, we show that disruption of MT-binding is central to
DCX pathology. In human induced pluripotent stem cell (hiPSC)-derived
cortical i3Neurons genome-edited to express DCX-mEmerald from the
endogenous locus, DCX-MT interactions polarize very early during neuron
morphogenesis. DCX interacts with MTs through two conserved DCX domains
that bind between protofilaments and adjacent tubulin dimers, a site that
changes conformation during GTP hydrolysis. Consequently and consistent
with our previous results, DCX specifically binds straight growth cone MTs
and is excluded from the GTP/GDP-Pi cap recognized by EB1. Comparing
MT-bound DCX fluorescence to mEmerald-tagged nanocage standards, we
measure approximately one hundred DCX molecules per micrometer growth cone
MT. DCX is required for i3Neuron growth cone advance in soft
microenvironments that mimic the viscoelasticity of brain tissue, and
using high resolution traction force microscopy, we find that growth cones
produce comparatively small and transient traction forces. Given our
finding that DCX stabilizes MTs in the growth cone periphery by inhibiting
MT depolymerization, we propose that DCX contributes to growth cone
biomechanics and reinforces the growth cone cytoskeleton to counteract
actomyosin generated contractile forces in soft physiological environments
in which weak and transient adhesion-mediated traction may be insufficient
for productive growth cone advance.