Morphogenetic activity of human brain neuroepithelium during early neurulation

BACKGROUND: During the embryonic period, from the development of the first neural folds to the formation of the primary closure zone of their edges, the neural plate undergoes active transformations. According to general concepts, the first structural signs of nervous system formation appear during neurulation at Carnegie stage 8. At stage 10, the neural plate begins to transform into a tube. During neurulation, the developing elements of the nervous system are most sensitive to damaging influences; however, this period of embryonic neurogenesis remains the least studied.

AIM: The work aimed to clarify the morphogenetic processes during the early stages of neurulation and to compare the sequence of provisional morphogenetic processes of the neuroepithelium in the region of the human brain.

METHODS: Eighteen human embryos obtained during autopsies of women who had died as a result of accidents were examined. After extraction of cytotrophoblasts from the uterine wall, macroscopic analysis, microdissection, and histological examination of the embryos were performed on serial sections.

RESULTS: The study of neurulation in the cranial region of human embryos revealed previously undescribed morphogenetic transformations of the neuroepithelium, including duplication of neural plate folds, formation of temporary neuroectodermal ridges, and other transient embryonic structures. These human-specific provisional morphogenetic events of the developing brain had remained unidentified, and their nature had not been explored.

CONCLUSION: Early embryonic morphogenesis of the human brain is a complex sequence of characteristic cenogenetic movements of the neuroepithelium. In the cranial portion of the neural plate, temporary (provisional) structures arise, sequentially altering the shape of the brain primordium. The emergence and disappearance of these structures likely reflect hidden mechanisms of positional information encoding that determine the subsequent differentiation of the main divisions of the human brain.