The ultrastructure of oral (buccopharyngeal) membrane formation and rupture in the chick embryo

Authors

  • Robert E. Waterman,

    Corresponding author
    1. Department of Anatomy, University of New Mexico, School of Medicine, Albuquerque, New Mexico 87131
    • All correspondence and reprint requests should be sent to: Robert E. Waterman, Ph.D., Department of Anatomy, The University of New Mexico, School of Medicine, Albuquerque, NM 87131
    Search for more papers by this author
  • Gary C. Schoenwolf

    1. Department of Anatomy, University of New Mexico, School of Medicine, Albuquerque, New Mexico 87131
    Current affiliation:
    1. Department of Anatomy, University of Utah, College of Medicine, Salt Lake City, UT 84132 USA
    Search for more papers by this author

Abstract

The ultrastructure of the oral (buccopharyngeal) membrane was examined by transmission and scanning electron microscopy (SEM) from its initial formation (stage 8) to its complete disappearance (stage 20) in the chick embryo. Thinning of the oral membrane prior to rupture occurs in large measure by increased interdigitation between cells of the stomodeal ectoderm and foregut endoderm coincident with a decrease in the width of the intervening extracellular space. Large numbers of necrotic cells were not observed. Interdigitation of ectodermal and endodermal cells makes it increasingly difficult to discern two discrete epithelia, and no evidence that one germ layer disappears prior to the other was observed. Changes occurred in the fine structure of the extracellular matrix during formation and rupture of the oral membrane, and the organization of this material within the oral membrane differed from that in regions immediately lateral to it. Copious amounts of amorphous, flocculant (“lamina-like”) material are present within the oral membrane at all stages. The basal lamina of the ectoderm exhibits small loops or folds at early stages. These decrease in number as the basal lamina becomes discontinuous prior to establishment of direct intercellular contact between cells of the ectoderm and endoderm across the intervening extracellular compartment. Initial perforations of the oral membrane are preceeded by clefts between cells on both sides of this structure, and SEM observations suggest that cells of the oral membrane continue to interdigitate, elongate, and change relative positions during the rupture process.

Ancillary