Vacuoles in the Embryonic Chick Corneal Epithelium, an Epithelium Which Produces Collagen

Studies on a variety of cells which excrete protein have established that synthesis of the protein occurs in the endoplasmic reticulum and that subsequent concentration, storage, and excretion occur via the Golgi apparatus (see Beams and Kessel, 1968 for review) . Ultrastructural radioautographie studies on the mode of collagen excretion, however, have been variously interpreted in respect to the role of the Golgi apparatus, with some investigators suggesting that collagen is processed by this organelle (Revel and Hay, 1963 ; Hay and Revel, 1969) and others suggesting that it is not (Ross and Benditt, 1965 ; Cooper and Prockop, 1968 ; Salpeter, 1968). An issue central to these studies has been the frequency of radioautographie detection of secretory vacuoles which contain radioactive protein . Despite the reported quantitative differences in the frequency at which labeled secretory vacuoles have been found, it should be emphasized that vacuoles containing ultrastructurally recognizable collagen, as well as dense vacuoles of unknown content, have been described in a variety of collagen-producing cells (Stearns, 1940 ; Fitton Jackson, 1960; Sheldon and Kimball, 1962; Movat and Fernando, 1962 ; Fernando and Movat, 1963 ; Revel and Hay, 1963 ; Voelz, 1964 ; Welsh, 1966 ; Welsh and Meyer, 1967; Reith, 1968 ; Hay and Revel, 1969) . The purpose of the present report is to describe two distinct types of vacuoles in an epithelium which produces collagen, namely the embryonic chick corneal epithelium . One type of vacuole contains cross-striated aggregates like collagen, and the other type has an elongated shape and contains a dense, slightly fibrillar material .