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Fig. 4. The dynamic pattern of EGFR activity detected with dp-ERK.
(A-C) Spatiotemporal patterns of dp-ERK in three successive stages of
invagination. Cells were labeled for dp-ERK (magenta), trh-lacZ
(green), GFP-Moesin (green) expression; DNA is shown in gray scale;
x-y and y-z sections of the same placode
(labeled with a and b, respectively) are shown for each time point. Additional
views of B are shown in Bc to Be. dp-ERK expression was initially detected in
the nucleus and the cytoplasm of a few cells in the dorsal side of the
tracheal placode (A, arrowhead) and subsequently expanded to fill the entire
dorsal half of the placode (B). dp-ERK showed a nuclear localization in the
peripheral region (arrowhead) and was concentrated in the apical cytoplasm in
the central region. Note that Bc is a deeper optical section of Ba and Bd
(position of the section is indicated by a thin white line in Bb). Apical
constriction had not yet occurred and only a mild degree of cell boundary
smoothing was observed at this stage (Bd). The dp-ERK signal was downregulated
after invagination (C). (D,E) dp-ERK expression in
Egfr+/- (D) and Egfr-/- (E) embryos.
D',E' show the dp-ERK signal. (F) rho-lacZ expression was very
similar to the pattern of dp-ERK. The tracheal placode (dashed outline) was
marked with KNI (Kni). (G) The overlap of KNI and trh-lacZ
expression. Scale bars: 10 µm.
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