Fig. 3. Recruitment of prospective PXM is delayed during gastrulation in Bmpr-MORE embryos. (A,A') No allantoic bud stage. Brachyury was expressed in the primitive streak (A, arrow), node and notochord of control embryos. The rostral end of the notochord was at the anterior of the embryo (A, arrowhead). The expression of Brachyury did not extend to the anterior in Bmpr-MORE embryos (A', arrow and arrowhead). (B-C') The early to late allantoic bud stage. Foxa2 was expressed in the node (B, lower arrowhead) and notochord of control embryos. Upper arrowheads indicate embryonic/extra-embryonic border. As the node is formed at the distal region of the primitive streak, the length of the primitive streak corresponds to the length between two arrowheads. The length of the primitive streak of Bmpr-MORE embryos was shorter compared with that of control embryos (B', arrowheads). Definitive endoderm develops in the mutant embryo (B', arrow). (C,C') Noggin was expressed in the node (lower arrowheads). The length of the primitive streak was shorter in mutant embryos (distance between arrowheads). (D,D') The head-fold stage. (D) Tbx6 was expressed in the mesoderm except axial mesoderm (between arrowheads). (D') The length of the primitive streak appeared to be similar between control and Bmpr-MORE embryos (distance between arrowheads). (E,E') The late streak stage. Lefty2 was expressed in LPM and PXM (between arrowheads). (E) In Bmpr-MORE, Lefty2 expression was decreased (E', between arrowheads). (F-G') The early to late allantoic bud stage. Lefty2 was expressed in migrating LPM and PXM (F, black and red arrowheads, respectively). In Bmpr-MORE, the migrating LPM expressed Lefty2 (F', black arrowhead). More recently recruited mesoderm expressing Lefty2 was observed at the middle and distal regions of the primitive streak (F', red arrow and arrowhead, respectively). Pcdh8 (PAPC on figure) was also expressed in LPM and PXM (G, black and red arrowheads, respectively). In Bmpr-MORE, the migrating LPM expressed Pcdh8 (G', black arrowhead). More recently recruited mesoderm expressing Pcdh8 was observed at middle and distal regions of the primitive streak (G', red arrow and arrowhead, respectively). Lefty2 was not expressed at the head-fold stage in control embryos (H). In Bmpr-MORE embryos, Lefty2 was still strongly expressed at distal and middle embryonic region (H', arrowhead and arrow, respectively). Scale bars: 100 µm for A,A',E,E'; 250 µm for B-D'; 200 µm for F-H'.