Expression of the avian alpha 7-integrin in developing nervous system and myotome

Integrins are cell surface receptors for a variety of extracellular matrix molecules including fibronectin, laminin and collagens. Although their role in development is not completely understood, they are likely to have important functions in cell migration and axon guidance. To characterize the types of integrins expressed in the developing nervous system, we have used monoclonal antibodies against alpha 7- and alpha v-integrin subunits to examine the distribution of these subunits in the early chick embryo. Low levels of alpha 7 immunoreactivity were first observed in the neural tube and developing myotome of stage 17 embryos (E2.5). Although low levels of alpha 7 expression were associated with most neuroepithelial cells, distinct alpha 7 immunoreactivity was first detected in the ventrolateral portions of the neural tube at a stage corresponding to the time when the first neurons differentiate. Its distribution pattern overlapped with that of commissural neurons in the developing spinal cord. alpha 7 was also prominently localized to the motor neurons and their axons emanating from the neural tube. In addition, alpha 7 immunoreactivity was observed on a subpopulation of trunk neural crest cells migrating through the somitic sclerotome. At later stages, alpha 7 expression was observed in other nervous system structures such as the pigmented retinal epithelial cells. In addition to its distribution in the developing nervous system, alpha 7 immunoreactivity was associated with early myotomal cells shortly after myotome formation and its expression persisted throughout myotome development. In contrast to alpha 7, alpha v-integrin had a limited distribution in the nervous system, being expressed only at low levels in the neural tube. However, alpha v displayed prominent immunoreactivity in the myotome and in endothelial cells of the dorsal aorta. The results suggest that alpha 7-integrin is one of the prevalent integrin subunits on neurons and axons in the developing spinal cord.