Differential expression of two cell adhesion molecules, Ephrin-A5 and Integrin alpha6, during cranial neurulation in the chick embryo.

The formation of the neural tube (neurulation) depends on the physical properties of the cells and tissues both inside and outside the neural plate. One such important physical property is cell adhesion. Theoretical and biological evidence support a role for cell adhesion in neurulation, but few specific cell adhesion molecules have been identified during this process. Ephrin-A5 and Integrin alpha6 are two of the known genes encoding cell adhesion molecules that are likely to be directly involved in neurulation because neural tube defects result when they are knocked out in mice. Yet it remains unclear how they can act on the cell and tissue behaviors of neurulation, because their domains of expression in neurulating tissues have not been reported. We report here the detailed pattern of expression of these two cell adhesion molecules in the chick embryo throughout the stages of neurulation at the mRNA and protein level. We show that Ephrin-A5 and Integrin alpha6 are differentially expressed in the ectoderm, outside and inside the neural plate, respectively, and that they are both restricted to neurulation at cranial (brain) levels. We discuss the potential contribution of this differential expression to the cell adhesion mechanisms involved in cranial neurulation and anencephaly.