CHANGES IN CELL-ADHESION AND EXTRACELLULAR-MATRIX MOLECULES IN SPONTANEOUS SPINAL NEURAL-TUBE DEFECTS IN AVIAN EMBRYOS

Quail embryos (embryonic days 2-2.5) with spontaneous neural tube defe cts (NTDs), along with age-matched normal embryos, were examined immun ocytochemically for the extracellular matrix (ECM) molecules laminin, fibronectin, and chondroitin sulfate proteoglycan, the cell adhesion m olecules (CAMs) E- and N-cadherin and neural CAM (NCAM), and the neura l crest marker HNK-1. The embryos with NTDs were at the lower limit of the normal stage range and the affected region was about 25% shorter than in normal embryos. Open NTDs occurred in cervical and upper thora cic level, although often the ventral neural tube was morphologically normal. Widened, irregular but closed neural tubes (lower thoracic to sacral levels) showed disorganized mesenchyme-like cells centrally and often multiple lumens. Finger-like tabs projecting from the ectoderm over the neural tube also occurred at lower thoracic to sacral levels. In open NTDs, the E-cadherin-labeled epidermis was incomplete dorsall y, and was continuous with the N-cadherin-labeled neural tissue, with a sharp demarcation between E- and N-cadherin-expressing regions, as i n the early stages of normal primary neurulation. A sharp inverted pea k of epidermis extended ventrally, closely applied to the side of the neural tissue. The intervening matrix labeled less intensely for chond roitin sulfate proteoglycan relative to laminin and fibronectin, in co mparison to control embryos. In closed NTDs, the dorsal superficial ce ll layer (i.e., positionally epidermis) was not separated from the und erlying neural tissue by a band of matrix as in control embryos. In ad dition, this layer expressed E-cadherin (as in normal embryos), but co expressed N-cadherin and NCAM, which are not normally found here at th is stage. This overlap region resembled the mid-dorsal tissue at earli er stages in normal secondary neurulation in the tail-bud. The tabs of tissue appeared to be localized hypertrophy of the epidermal and neur al ectoderm, and also showed codistribution of E- and N-cadherin. In a ll these defects, matrix molecules occurred within (rather than around ) the neural and epidermal epithelia. HNK-1-labeled neural crest cells were frequently absent in regions of NTDs, in contrast to control emb ryos. These results show that matrix and cell adhesion molecules are d isturbed in spontaneous NTDs at the time of neurulation, and therefore could be involved in the generation of the defects by altering cell a dhesion-dependent morphogenetic events. (C) Wiley-Liss, Inc.