Figure 4.
Figure 4. Characterization of distinct CB membrane domains involved in lumen formation. Dorsal XY views of wild-type cardiac tubes (A–C and D–D″) and reconstructed Z views of wild-type CBs (A′–C′, E-–J, E′–J′, and E″–J″). (A and A′) Dg (green) and How (blue, showing CB nuclei) staining. (B and B′) Trol expression revealed using Trol-GFP reporter. (C and C′) Slit expression. Notice that Dg, Trol, and Slit are expressed at the basal side (arrowheads) and at the luminal side (double-sided arrows) of the CBs in the membrane domain forming the lumen (L domain). (D–D″) Wild-type embryo stained with antibodies against Arm (red), Dg (green), and How (blue) at stage 16. (D′, arrowhead) Arm is localized in the basolateral membranes involved in cell–cell contact between CBs of the same row. (E–J) Merged Z views of wild-type CBs from stages 13–14 in E to stage 16 in J, stained with antibodies against Arm (red), Dg (green), and How (blue). (E′–J′ and E″–J″) The same views as E–J showing Arm and How (E′–J′) or Dg and How staining (E″–J″). Arm is localized at the future contact between the two CBs (arrowheads), at the dorsal leading edge, and at the ventral side. Arm is excluded from Dg-positive domain (basal and luminal faces), before (E–E″, arrowheads), during (F–I, F′–I′, and F″–I″, arrowheads), and after CB migration (J–J″, arrowheads). When CBs join dorsally, Arm is strongly expressed at the site of contact between the two CBs (G–J, G′–J′, and G″–J″, arrowheads). When the ventral sides join to close the tube, Arm is specifically localized at the site of cell–cell contacts (dorsal and ventral; J and J′, arrowheads) and excluded from the lumen domain where Dg is expressed (J″). The Arm-positive domains and forming adherens junctions between CBs of opposite rows are called J domains. (K) Schematic representation of CB morphogenesis during cardiac tube formation. Gray, CBs; red, Arm; green, Dg; blue dashed lines, Z section positions; purple arrows, CB shape changes. (1) Before CB migration, CBs are rather round and already express Arm in the J domains and Dg in the L domains. (2) CBs constrict and form a leading edge dorsally. (3) They join first dorsally, then adopt a crescentlike shape (4), and finally meet ventrally and close the tube (5). Bars, 4 μm.

Characterization of distinct CB membrane domains involved in lumen formation. Dorsal XY views of wild-type cardiac tubes (A–C and D–D″) and reconstructed Z views of wild-type CBs (A′–C′, E-–J, E′–J′, and E″–J″). (A and A′) Dg (green) and How (blue, showing CB nuclei) staining. (B and B′) Trol expression revealed using Trol-GFP reporter. (C and C′) Slit expression. Notice that Dg, Trol, and Slit are expressed at the basal side (arrowheads) and at the luminal side (double-sided arrows) of the CBs in the membrane domain forming the lumen (L domain). (D–D″) Wild-type embryo stained with antibodies against Arm (red), Dg (green), and How (blue) at stage 16. (D′, arrowhead) Arm is localized in the basolateral membranes involved in cell–cell contact between CBs of the same row. (E–J) Merged Z views of wild-type CBs from stages 13–14 in E to stage 16 in J, stained with antibodies against Arm (red), Dg (green), and How (blue). (E′–J′ and E″–J″) The same views as E–J showing Arm and How (E′–J′) or Dg and How staining (E″–J″). Arm is localized at the future contact between the two CBs (arrowheads), at the dorsal leading edge, and at the ventral side. Arm is excluded from Dg-positive domain (basal and luminal faces), before (E–E″, arrowheads), during (F–I, F′–I′, and F″–I″, arrowheads), and after CB migration (J–J″, arrowheads). When CBs join dorsally, Arm is strongly expressed at the site of contact between the two CBs (G–J, G′–J′, and G″–J″, arrowheads). When the ventral sides join to close the tube, Arm is specifically localized at the site of cell–cell contacts (dorsal and ventral; J and J′, arrowheads) and excluded from the lumen domain where Dg is expressed (J″). The Arm-positive domains and forming adherens junctions between CBs of opposite rows are called J domains. (K) Schematic representation of CB morphogenesis during cardiac tube formation. Gray, CBs; red, Arm; green, Dg; blue dashed lines, Z section positions; purple arrows, CB shape changes. (1) Before CB migration, CBs are rather round and already express Arm in the J domains and Dg in the L domains. (2) CBs constrict and form a leading edge dorsally. (3) They join first dorsally, then adopt a crescentlike shape (4), and finally meet ventrally and close the tube (5). Bars, 4 μm.

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