HypFIG3: Embryonic hypodermal morphogenesis and major morphogenetic movements at 20oC.
The first cleavage is time 0 (based on Chin-Sang and Chisholm, 2000; Simske and Hardin, 2001; Chisholm and Hardin, 2005).
A. Gastrulation, approximately 100-250 minutes (DIC image), lateral view. Around the 26-cell stage, a gastrulation cleft (arrowhead) is created on the ventral side of the embryo, through which the germline, gut, and mesodermal precursors will move into the embryo (curved arrow).
B. Approximately 230-290 minutes (DIC image), ventral view. Gastrulation cleft closes by movement of ventral ectodermal (mostly neuroblasts) cells (arrows).
C. Approximately 290-340 minutes; dorsal hypodermal intercalation (DIC image), dorsal view. Neighboring cells move in opposite directions during intercalation (arrows).
D. Approximately 310-360 minutes; ventral hypodermal closure (DIC image), ventral view. Ventral pocket cells seal the pocket in the direction shown by arrows.
E. Approximately 360-600 minutes; hypodermal cell fusions and elongation of the embryo. Epifluorescent images of transgenic animals expressing the ajm-1::GFP reporter in the hypodermis. This marker gene is expressed at the apical borders of all epithelia and is required for the integrity of epithelial junctions (Koeppen et al., 2001). (Top) Tadpole-stage embryo lateral view; (bottom) threefold embryo, lateral view. (H) head; (T) tail; (h6) hyp 6; (h7) hyp7. Anterior seam cells (H1 and H2 in tadpole stage and H2, V1 and V2 in threefold-stage embryo) are marked. Arrowheads point to anterior deirid. (Strain source: H. Yu and P. W. Sternberg.)
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