Doublecortin reinforces microtubules to promote growth cone advance in soft environments.

Doublecortin (DCX) is a microtubule-associated protein critical for brain development. Although most highly expressed in the developing central nervous system, the molecular function of DCX in neuron morphogenesis remains unknown and controversial. We demonstrate that DCX function is intimately linked to its microtubule-binding activity. By using human induced pluripotent stem cell (hiPSC)- derived cortical i 3 Neurons genome engineered to express mEmerald-tagged DCX from the endogenous locus, we find that DCX-MT interactions become highly polarized very early during neuron morphogenesis. DCX becomes enriched only on straight microtubules in advancing growth cones with approximately 120 DCX molecules bound per micrometer of growth cone microtubule. At a similar saturation, microtubule-bound DCX molecules begin to impede lysosome transport, and thus can potentially control growth cone organelle entry. In addition, by comparing control, DCX-mEmerald and knockout DCX -/Y i 3 Neurons, we find that DCX stabilizes microtubules in the growth cone peripheral domain by reducing the microtubule catastrophe frequency and the depolymerization rate. DCX -/Y i 3 Neuron morphogenesis was inhibited in soft microenvironments that mimic the viscoelasticity of brain tissue and DCX -/Y neurites failed to grow toward brain-derived neurotrophic factor (BDNF) gradients. Together with high resolution traction force microscopy data, we propose a model in which DCX-decorated, rigid growth cone microtubules provide intracellular mechanical resistance to actomyosin generated contractile forces in soft physiological environments in which weak and transient adhesion-mediated forces in the growth cone periphery may be insufficient for productive growth cone advance. These data provide a new mechanistic understanding of how DCX mutations cause lissencephaly-spectrum brain malformations by impacting growth cone dynamics during neuron morphogenesis in physiological environments.

A case series of CHARGE syndrome: identification of key features for a neonatal diagnosis.

BACKGROUND: An early diagnosis of CHARGE syndrome is challenging, especially for the primary care physicians who often take care of neonates with multiple congenital anomalies. Here we report eight cases of CHARGE syndrome whose diagnosis was made early in life with the intent to identify the most helpful features allowing a prompt clinical diagnosis. METHODS: Medical records of patients with CHARGE syndrome whose diagnosis was made at the Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico in Milan, Italy were retrospectively reviewed. RESULTS: Taken together, these patients reflect the considerable phenotypic variability of the syndrome; in one patient, the diagnosis was made immediately after birth because all the major criteria were met. In six patients, presenting with relatively nonspecific defects, a temporal bone computerized tomography scan was essential to achieve the correct diagnosis. In one patient, the diagnosis was made later than the others were. A careful examination revealed the presence of outer, middle, and inner ear anomalies: these elements, in the absence of any additional major criteria, represented for us an important diagnostic clue. CONCLUSIONS: This article suggests that an accurate evaluation of the ear should be made every time CHARGE syndrome is considered as a likely diagnosis even when the standard criteria are not fulfilled.