Keratinization of sheath and calamus cells in developing and regenerating feathers

The present ultrastructural and immunocytochemical study on developing and regenerating feathers in the chick, zebrafinch and quail describes the formation of alpha-keratin cells in the sheath and their transition into beta-keratin cells in the calamus. In the first stages of feather formation cells are produced in the lower part of the follicle, migrate upward and form the elongating sheath of the feather filaments that grows outside the...