Cell junctions during morphogenesis of feathers: general ultrastructure with emphasis on adherens junctions

The present ultrastructural and immunocytochemical study analyzes the cell junctions joining barb ⁄ barbule cells versus cell junctions connecting supportive cells in forming feathers. Differently from the epidermis or the sheath, desmosomes are not the prevalent junctions among feather cells. Numerous adherens junctions, some gap junctions and fewer tight junctions are present among differentiating barb ⁄ barbule cells during early stages of their differentiation. Adherens junctions are frequent also among differentiating supportive cells and show weak immunolabeling for both N-cadherin and neural-cell adhesion molecule (N-CAM). Differentiating barb and barbule cells do not show labeled junctions for N-cadherin and N-CAM. The labeling occurs at patches in the cytoplasm of supportive cells but is more frequently seen in the external cytoplasm and along the extra-cellular space (glycocalix) covering the plasma membrane of supportive cells. Labeling for N-cadherin is also found in medium-dense 0.1- to 0.3-lm granules present in supportive cells and sometimes is associated with coarse filaments or periderm granules. The study indicates that adherens junctions form most of the transitional connections among supportive cells before their degeneration. Keratinizing barb and barbule cells loose the labeling for adherens junctions (N-CAM and N-chaderin) while their adhesion is strengthened by the incorporation of cell junctions in the corneous mass forming the barbules.