Fig. 4. Cell lineage analyses of control and mutant mesoderm cells. DiI was applied to the primitive streak mesoderm (A-F). After culture, embryos were observed under visible light (A'-F') or ultra violet light (A''-F''). (A-B'') DiI was injected into the proximal region of the primitive streak (arrowheads) of control (A) or mutant embryos (B) at the late streak stage. Arrows indicate the embryonic/extra-embryonic border. Embryos injected with DiI were cultured for around 30 hours (A',A',B,B', ventral view). Mesoderm cells derived from proximal primitive streak of control embryos contributed to lateral plate (A', arrowhead and yolk sac, A'', arrow), but not to somites (A',A'', asterisk). In Bmpr-MORE embryos, mesoderm cells derived from proximal primitive streak contributed to regions anterior and lateral to paraxial region (B',B'', arrowheads and arrow, respectively) but apparently not to the paraxial region (B',B'', asterisks). (C-D'') DiI was injected into the anterior-to-distal region of the primitive streak (arrowheads) of control (C) or mutant (D) embryos at the late streak stage. Embryos injected with DiI were cultured for around 30 hours (C' and C'', dorsal view; D' and D'', ventral view). (C',C'') Mesoderm cells derived from the anterior- to-distal primitive streak of control embryos contributed to somites (asterisks) and to an axial structure (red arrows and arrowheads, respectively), but not to lateral plate (blue arrows) (see inset). (D',D'') In Bmpr-MORE embryos, mesoderm cells derived from the anterior-to-distal primitive streak contributed to a region anterior to somites (arrowhead) and an axial structure (arrow). (E-F'') DiI was injected into the middle region of the primitive streak (E,F, arrowhead) of control and mutant embryos of the head-fold stage. Arrows indicate the length of the primitive streak. Embryos injected with DiI were cultured for around 24 hours. (E',E'') Dorsal views. (F',F'') Ventral view. (E',E'') In control embryos, mesoderm cells derived from middle primitive streak contributed to lateral plate mesoderm (arrowheads), but not to somites (asterisks). (F',F'') In Bmpr-MORE embryos, mesoderm cells derived from middle primitive streak mainly contributed to lateral row of somites (arrowhead) and fewer mesoderm cells contributed to medial row of somites (arrow). Scale bars: 100 µm for A-D; 250 µm for and E,F; 300 µm for A-B'',D-F''; 600 µm for C',C''.