COOPERATIVE MODEL OF EPITHELIAL SHAPING AND BENDING DURING AVIAN NEURULATION - AUTONOMOUS MOVEMENTS OF THE NEURAL PLATE, AUTONOMOUS MOVEMENTS OF THE EPIDERMIS, AND INTERACTIONS IN THE NEURAL PLATE EPIDERMIS TRANSITION ZONE

Morphogenetic movements during neurulation cause a tissue to change sh ape within the plane of the epithelium (e.g., conversion of the oval n eural plate into the narrow spinal plate and the wide brain plate), ca use bending out of the plane of the epithelium (e.g., raise the neural folds and curl the neural plate into a tube), or contribute to both p henomena. In this study, pieces that contain neural plate alone, epide rmis alone, or both tissues (with or without underlying tissues) are c ut from chick embryos and allowed to develop for up to 24 hr. Examinat ion of histological sections through such isolates allows analysis of the formation of neural folds. When the neural plate/epidermis transit ion zone is disrupted, neural folds do not form. Conversely, when the transition zone remains intact, neural folds form. Neural folds form e ven when most of the medial neural plate and lateral epidermis has bee n removed, leaving only the isolated transition zone. These data indic ate that the transition zone is both necessary and sufficient for the formation of neural folds. The transition zone may play a number of ro les in epithelial bending including organizing, focussing, and redirec ting movements that are autonomous to the neural plate or epidermis. T ime-lapse video recording, and sequential photographs allowed the docu mentation of such movements. Neural plate isolates exhibit autonomous rostrocaudal lengthening and mediolateral narrowing. Isolated strips o f epidermis exhibit autonomous movements which, unlike wound-healing m ovements, are unidirectional (mediad), and region-specific (beginning and reaching their greatest extent in the cranial region). Isolated pi eces of neural plate or epidermis remain flat instead of bending, prov iding further evidence that the transition zone is necessary for the f ormation of neural folds. (C) 1995 Wiley-Liss, Inc.