|
Fig. 1 The method used for making the fate map for endoderm. A single cell on the blastoderm margin was co-injected with rhodamineand biotin-dextran at mid-blastula (1000-cell stage, 3 hours). (A) At 40% epiboly, the clone (now 4 deep cells and 1 enveloping layer cell; asterisk) was examined in face view. The distance of each cell from the blastoderm margin (arrow) was measured in terms of cell diameters. In this clone, one cell lies just below the margin and was designated in tier 0, the other cells were in tiers 1 and 2. (B) At shield stage, the clone was re-examined from an animal pole view. Frequently, the number of deep cells was the same. The distance between the dorsal midline (arrow) and the center of the clone was measured in degrees of arc. By now, all labeled deep cells had involuted; asterisk, enveloping layer cells. (C) Depiction of the blastoderm at 40% epiboly and the position of the mapped clone. Although the clone was on the right, it is projected to the left side of the blastoderm for conventional presentation (Kimmel et al., 1990). (D,E) At 30 hours, the deep cell clone formed part of an epithelial layer overlying the yolk sac. (D) Dorsal view. (E) Lateral view. The arrow indicates the same group of cells. (F,G) By 96 hours, the deep cell clone had become pharyngeal endoderm within the gills. (F) Ventral oblique view of the live embryo, anterior to the right. The clone, between the right eye and left ear, was near pharyngeal cartilage. (G) Lateral view, after whole-mount staining for the fixable tracer. The cells of the endodermal clone, now stained brown (arrow), formed a simple squamous epithelium covering the gills. (H,I) Depiction of the developing digestive tract (bold outline). (H) At 48 hours, the gut tube. Only the pharyngeal pouches, early pharynx, have noticeably differentiated. (I) At 96 hours, the gut is fully differentiated. The subdivisions include (progressing rostro-caudally): the pharynx (including gills), the esophagus, the stomach and the intestine. The liver (left), swimbladder (medial), and pancreas (right; shaded) are diverticula of the gut. (J-P) Whole-mount-stained clones between 96 and 120 hours of development illustrating differentiated endodermal tissues. (J-M,P) are left side presentations, (N,O) are right side; arrows indicate labeled cells within each structure; asterisks indicate lumens. (J) Pharynx: simple squamous epithelium. (K) Esophagus: stratified squamous epithelium. (L) Liver (outlined in arrowheads): parenchymal cells. (M) Swimbladder: pseudostratified squamous epithelium. (N) Stomach: simple columnar epithelium. (O) Pancreas: parenchymal cells containing prominent vesicles (putative zymogen granules). (P) Intestine: simple columnar epithelium. Scale bar: 50 μm (A,F,G), 200 μm (B), 100 μm (D,E), 25 μm (J-P). Abbreviations: a, pancreas; b, swimbladder; e, esophagus; i, intestine; l, liver; p, pharynx; s, stomach; ey, eye; ov, ear; pc, pharyngeal cartilage; pp, pharyngeal pouches.