Relationships between egr2, cyp26b1, cyp26c1, and RA Signaling
(A–H) Effect of egr2a plus egr2b knockdown (egr2 morpholino oligonucleotides [MO]) on cyp26b1 and cyp26c1 expression. egr2 knockdown increases the level of cyp26b1 expression in r3 (black arrowhead) at 13 hpf (B) and 15 hpf (F), and of cyp26c1 in r3 and r5 (black arrowheads) at 13 hpf (D) and 15 hpf (H) compared with control embryos (A, C, E and G). r3∗ and r5∗ in (B), (D), (F), and (H) refer to the region specified as r3 or r5 in the presence of egr2.
(I–P) Expression of cyp26b1 and cyp26c1 in control embryos and after induction of widespread egr2 expression by heat shock of hs-egr2b embryos at 11.3 hpf. Widespread expression of egr2b leads to reduction of cyp26b1 expression in r4 (black arrowhead) at 13 hpf (J), and 15 hpf (N) compared with control embryos (I and M). Similarly, cyp26c1 expression is reduced in r2, r4, and, to a lesser extent, in r6 (black arrowheads) at 13 hpf (L) and 15 hpf (P) in comparison with control embryos (K and O).
(Q–T) hs-egr2b embryos subjected to heat shock at 11.3 hpf in the presence (S and T) or absence (Q and R) of the pan-RAR antagonist AGN193109. Endogenous egr2b expression was analyzed at 16.5 hpf. In DMSO-treated control embryos, endogenous egr2b is expressed in r2, r4, and r6, but to a lesser extent in ventral r4 (Q and R). In AGN193109-treated embryos, expression of endogenous egr2b in r2, r4, and r6 is more heterogeneous and there are patches of cells that do not express endogenous egr2b (black arrowheads in S and T).
Embryos in (A)–(P) are flat-mounted with anterior to the top; embryos in (Q) and (S) are flat-mounted with anterior to the left; embryos in (R) and (T) are side-mounted with anterior to the left. Dashed lines in (Q)–(T) indicate presumptive rhombomere borders. Scale bars: 50 μm.