InterFIG 5: Embryonic development of buccal cavity.

A, C, E. Schematic views of buccal development. (Yellow) Arcade cells; (purple) pharyngeal epithelial cells; (dark green and light green) pharyngeal muscle cells. The anterior sensory deprivation (not a mouth opening) is indicated with a star in A. Black curved lines on cells indicate epithelization and apical-basal domain separation (Based on Portereiko and Mango, 2001; Mango, 2007). B, D, G DIC images corresponding to different embryonic stages: B comma stage; D 1.5-fold stage; G twofold stage. (Black arrowheads in DIC images) Basal lamina surrounding the pharynx primordium; (black arrows) pharyngeal epithelial cells; (white arrows) arcade cells. Buccal and anterior pharyngeal development has three stages: reorientation of pharyngeal epithelial cells (A-C), epithelization of arcade cells (D, E) and contraction of the arcade and pharyngeal epithelium (E inset, G). In the first stage, pharyngeal epithelial cells reorient their polarity to dorsoventral from rostrocaudal axis (double-headed arrows in A and C) to align with arcade cells. This rearrangement changes the shape of the pharynx from a cyst to a short tube. In the second stage, arcade cells become epithelialized, producing a continuous epithelium with the pharyngeal tissue and coupling the buccal cavity to the anterior hypodermis and the pharynx. In the last stage, apical surfaces of the arcades and pharyngeal epithelial cells constrict, pulling the pharynx anteriorly and the buccal opening posteriorly. A tube without a lumen is formed at the end of the third stage. F Image of a fluorescently labelled 2-fold embryo. By the 1.75-fold stage the cell bodies of arcades (white arrows) have begun to move away. By the 2-fold stage, they are seen at various positions outside of the basement membrane that surrounds the foregut (arcades are never seen inside the pharyngeal basement membrane). Green is LAM-3, which marks the basement membrane, red is PHA-4, which marks the pharyngeal cells and arcades, white is DLG-1, which marks the adherens junctions (image source: S. Von Stetina) (Based on Von Stetina & Mango, 2015)

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