Fig. 3. Myosin and RhoGEF2 fail to uniformly assemble a contractile network in abl mutants. Embryos, antigens and genotypes are indicated. (A-F'') Cross-sections. (A-D) Low magnification. (A,B) Myosin in the basal furrow canals (arrows) in wild type (A) and abl mutants (B) at late cellularization. (C,D) Mesoderm in the early VF. Myosin disappears basally (arrowheads) and accumulates apically (arrows) in wild type (C) and abl mutants (D). (E-F'') Close-ups of the VF. (G-H'') Grazing-sections. (E-E'',G-G'') Myosin accumulates apically in wild-type constricting cells (arrow). (F-F'',H-H') Myosin concentrates in constricting cells (arrows) in abl mutants, but is diffuse in unconstricting cells (arrowheads). (I-N'') Cross-sections taken at late cellularization-gastrulation onset. (I-K) Wild type. RhoGEF2 is lost basally in mesoderm (I, arrow vs arrowhead), and then accumulates apically (J,K, arrows). (L) abl mutant. RhoGEF2 accumulates apically (arrow). (M-N'') Cross-sections of the VF. (O,P) Grazing-sections of the VF. (M,O) In wild-type embryos, RhoGEF2 localizes strongly to all cells (arrows). (N,P) In abl mutants, RhoGEF2 localizes apically in constricting cells (arrows), but is diffuse in non-constricting cells (arrowheads). (Q,R) Cross-sections of the VF showing the expression of P-Myo by constant-level imaging. Similar levels of Myo-P (P-Myo) were observed at apical constriction sites (arrows) in wild type (Q) versus abl mutants (R). Myo, Myosin; GEF, RhoGEF2; Arm, Armadillo; P-Myo, Phospho-Myosin. Scale bar: 20 µm.