Formation and perforation of closing plates in the chick embryo

Abstract

The morphology of the closing plates between adjacent pharyngeal arches was examined in chick embryos between stages 11 and 21 (Hamburger-Hamilton). Each closing plate is formed by apposition between the basal surfaces of portions of the pharyngeal pouch endoderm and the ectoderm of the overlying pharyngeal cleft. Initial contact between ectoderm and endoderm occurs at several small points which are separated by regions containing mesenchymal cells and extracellular material. Contact between the opposed epithelia is made by extension of cellular processes through the intervening basal laminae and extracellular space. Endodermal and ectodermal cells then interdigitate to create a cellular layer which rapidly thins. The interposed extracellular material is sequestered into small pools as cellular interdigitation proceeds. Perforations form through certain regions of closing plates 1-3 and persist during the stages studied. Small slit-like depressions appear between cells of the closing plate just prior to perforation. The initial perforations enlarge until they are separated only by thin cellular strands. These strands presumably rupture, leaving small cellular accumulations which persist for a short time marking the junction between ectoderm and endoderm along the walls of adjacent pharyngeal arches. Clear evidence of cell degeneration is rare. These results suggest that cellular reorganization, rather than cell death, is a major mechanism of initial perforation.

The odontode explosion: The origin of tooth‐like structures in vertebrates

“…Strikingly similar conditions also hold for the ectoderm-endoderm contact areas between individual pharyngeal pouches and corresponding pharyngeal clefts where these epithelia together form so-called branchial membranes (e.g. [49, 50, 53–56]). As in the case of oral development, perforation of the branchial membranes probably causes a loss of definitive ectoderm-endoderm boundaries.…”

Apoptosis removes chick embryo tail gut and remnant of the primitive streak

“…We also looked for apoptotic markers in pharyngeal closing plates where cell death is not considered to be part of the rupture process (Waterman, 1985). We did not find apoptosis markers in these ephemeral membranes of five embryos representing stages 16-22.…”

Dynamic epithelia of the developing vertebrate face

“…Virtually nothing is known about the genetic control of the invagination of clefts and their fusion with pouches. Cleft epithelial cells have been observed to extend filopodia towards budding pouches, and a recent morphological analysis in avians and zebrafish showed dissolution of the basement membrane separating endodermal and ectodermal epithelia during fusion, as well as localized cell death at pouch/cleft contact points (Table 1) [34,35]. A bit more is known about fusions of the more anterior endoderm with the oral ectoderm to form the buccopharyngeal membrane and eventually the primary mouth, a process likely similar in nature to what occurs between pouch and cleft epithelia (Table 1) [5].…”