Molecular and morphogenetic features of neurulation

Abstract

Neurulation occurs by two different mechanisms, called primary and secondary neurulation. In humans, primary neurulation occurs along most of the rostrocaudal axis of the embryo, while secondary neurulation occurs caudally, only in the lower sacral and coccygeal regions. Primary neurulation is responsible for a change in the neural plate shape, the lateral edges of which rise and then converge at the dorsal midline to merge into a tube. Initially, the neural tube, formed as a result of primary neurulation, is open at both ends through the so-called rostral and caudal neuropores. These neuropores connect the inner part of the neural tube with the environment (amniotic cavity) and later (by the end of primary neurulation) are closed. During primary neurulation, the brain and spinal cord are formed up to the upper sacral region (up to the level of junction between S1 and S2 vertebral bodies), however, the most caudal part of this anatomical region (sacral-coccygeal division of the spinal cord, conus medullaris and filum terminale) is formed at secondary neurulation. In humans, secondary neurulation occurs due to elongation and cavitation of the caudal cell mass into the medulla, which then transforms into a secondary neural tube. Thus, the main differences between primary and secondary neurulation are that the neural plate folds and invaginates into the body of the embryo and separates from the surface ectoderm, forming an underlying hollow tube in primary neurulation. Mesenchymal cell сlusters form a dense cord that undergoes mesenchymal-epithelial transition and forms cavities and an empty tube during secondary neurulation to form the terminal part of the spinal cord. Conclusions. Understanding the detailed molecular and genetic mechanisms of each stage of neurulation is relevant due to widespread congenital neural tube defects, and only perfect knowledge on each aspect of neurulation and all possible factors of potential influence on it will help to develop modern options for influencing some of them, and probably, cause a decrease in neural tube congenital defects.