The neural tube is the embryonic precursor to the adult brain and spinal cord. Disruptions in its formation, a process known as neurulation, can result in severe birth defects called neural tube defects. Neurulation is a complex, multi-step morphogenetic process that transforms a flat sheet of cells into a neural tube. Cellular protrusions such as filopodia and lamellipodia have been proposed to play critical roles in this process (1). However, their involvement remains unclear, as most observations have been limited to fixed specimens, with limited live imaging data available to capture their dynamic behaviour (1 - 4).
We previously generated a transgenic LifeAct–EGFP quail line to study actin organisation and dynamics during morphogenesis in vivo (5). This model provides a unique opportunity to investigate the behaviour of protrusions in the developing neural tube. Using in vivo live imaging, we demonstrate that these protrusions are highly dynamic, continuously changing in shape and area over periods ranging from minutes to over an hour until the advancing zippering point of the neural tube reaches them. The protrusions extend from the edges of the neural tube into the lumen, sometimes establishing contact with the opposite neural fold. For the first time, we show that these protrusions actively contribute to neurulation by mechanically pulling the opposing neural folds together. Furthermore, our data reveal an intriguing spatial organisation of protrusions in the open neural tube, with their positions strongly correlating with developing somites and fibronectin deposition patterns. The precise mechanisms driving the timing and localisation of these specialised structures remain under investigation.
Elucidating how cellular protrusions facilitate neural tube closure may enhance our understanding of the aetiology of neural tube defects and guide the development of potential interventions for these common congenital disorders.