Neurocan is the most abundant lectican considered to be expressed exclusively in the central nervous system. Neurocan interacts with other matrix components, with cell adhesion molecules, growth factors, enzymes and cell surface receptors. The interaction repertoire and evidence from cellular studies indicated an active role in signal transduction and major cellular programs. Relatively little is known about the neurocan tissue-specific distribution and function during embryonic development. This study examined the time of appearance and subsequent spatio-temporal expression pattern of neurocan and its functional activities during the earliest stages of development in the chick embryo.
Neurocan was first detected in the inchoate neural plate and the extracellular matrix in embryos at the definitive streak stage (late gastrula). The expression of neurocan was very intense in the neural tube (developing central nervous system). Another significant observation was the very intense expression of neurocan in premigratory and migrating neural crest cells and in mesenchymal tissues known to be derived from the neural crest. Moreover, neurocan was intense in several areas of active cell migration such as the heart, the dispersing somite, the presumptive pronephric tubules and the blood islands.
Inhibition of neurocan function by blocking antibodies resulted in defects in the early embryo consistent with the known biochemical features and interactions of neurocan with signaling molecules: The neural epithelium expanded abnormally in the surface ectoderm (presumptive epidermis) flanking the neural tube showing a change of developmental fate from non-neural to neural possibly because of the diffuse spread of FGF signals. Surface ectoderm cells acquired invasive properties and interacted with the neuroepithelium while cranial neural crest cells formed ectopic aggregates on the apical side of the ectoderm possibly due to perturbation in the tight regulation of cadherin and N-CAM function. Neurocan seems to protect the functional organization of the extracellular matrix and to regulate the diffusion range and the local reception of FGF/BMP signalling activity during the neural-non-neural cell specification. Moreover, neurocan, through its interactions with cell surface molecules, seems to be an extracellular modulator of cell adhesive and signalling activities of epithelial-mesenchymal cells that are central to tissue patterning in the early embryo.
Neurocan was first expressed in the inchoate neural plate at the late gastrula stage. Neurocan expression was very intense in the developing central nervous system as well as in many non-neural tissues. Neurocan seems to modulate signalling in the neural-non-neural tissue specification and the adhesive and signalling activities of epithelial-mesenchymal cells and neural crest cell motility in the early embryo.