Anteroposterior elongation of the chicken anterior trunk neural tube is hindered by interaction with its surrounding tissues.

The neural tube is the precursor of the central nervous system. Its early formation and growth are known to be extremely biased along the anteroposterior (AP) axis. Several mechanisms including addition of cells from the tail bud, lateral pressure from surrounding tissues and oriented cell divisions have been proposed to contribute to this biased growth. Here we show that, contrary to what has been found in posterior regions encompassing the tail bud region, the growth of the anterior trunk neural tube is slower along the AP direction than in the other axes. We found that this is due to anchorage of the neural tube to the matrix which favors apicobasal elongation at the expense of AP growth. In addition, as the neural tube develops, we found a moderate slowdown of cell proliferation that could account for the overall reduction of the pace of 3D growth in the same time window. However, as we found no preferred orientation of cell division, changes in cell cycle pace are unlikely to directly contribute to the observed AP-hindered growth of neural tube. Overall, these data indicate that neural tube growth is not intrinsically positively biased along the AP axis. Rather it switches from AP-favored to AP-hindered regimes between the most posterior and anterior trunk neural tube regions.