Spatial and temporal expression of the 5A11/HT7 antigen in the chick embryo

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Abstract
The 5AII/HT7 antigen is the avian homologue of a 45-50X103 M r plasma membrane glycoprotein of the immunoglobulin super-gene family also identified in mammalian species (basigin, mouse gp42, MRC OX-47 antigen, M6 antigen). We had previously demonstrated that antibodies to this antigen interfere with heterotypic cell-to-cell interaction-dependent glial cell maturation in vitro. In this report, we sought to gain insight into its developmental role through an analysis of its distribution at various stages of avian embryogenesis. The primary mode of expression progresses from generalized staining of the undifferentiated tissue to intense labelling of specific cell types coincident with biochemical or morphological differentiation. In the retina, expression progresses from the generalized staining of the neural ectoderm, then, during neurogenesis, becomes restricted to Müller cells, photoreceptor cell bodies, the retina pigmented epithelium, the pigmented cells of the ciliary membrane and endothelia of the pecten. Similarly, the uniform staining of undifferentiated skin ectoderm progressively becomes confined to the germinative cells of the epidermis during biochemical differentiation of scutate and reticulate scales and formation of the feather follicle. During mesonephric and metanephric tubule development, labeling appears on those cells induced to form epithelia from the unlabeled mesenchyme and persists on the basal-lateral membranes of the convoluted tubules. Western blot analysis of NP-40 solubilized proteins from hatchling chicken identifies an immunoreactive polypeptide of 45-50X103 M r in tissues stained immunohistochemically and an additional band of 69X103 M r in the neural retina and pineal gland. The localization of the 5A11 antigen at boundaries typically associated with inductive interactions between cells and tissues suggests broad involvement in cell-to-cell interactions associated with cellular maturation.