The peri‐albumen layer: a novel structure in the envelopes of an avian egg

The present paper describes a novel structure, termed the peri‐albumen layer, in the egg‐envelopes of the quail Coturnix japonica. It reacts with Alcian blue and exists between the egg white and the shell membrane. Ultrastructurally, it is of fine granular structure and forms a fenestrate sheet, the width of which is 190 nm or less. Isolated materials of the peri‐albumen layer include an Alcian‐blue‐positive polysaccharide of 260 kDa, and three glycoproteins of 160, 108 and 52 kDa. The layer is supplied to an egg when it passes through the magnum–isthmus junction, the normalized length of which is 0.62–0.63 of the oviduct. The mucosa of the junction consists exclusively of a luminal epithelium. It is apparently distinct from the mucosa of the magnum and the isthmus, which consist of a luminal epithelium and tubular glands. The luminal epithelium of the magnum–isthmus junction stains prominently with Alcian blue and consists of alternately distributed ciliated cells and granular cells. Immunohistochemistry with an antiserum raised against the materials of the peri‐albumen layer revealed the staining of the peri‐albumen layer of the egg, and secretory cells of the luminal epithelium at the magnum–isthmus junction. It was concluded that the materials of the peri‐albumen layer are produced by secretory cells at the magnum–isthmus junction of the oviduct.