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Fig. 3. Mesodermal migration and patterning defects in Lrp5+/-;Lrp6-/- embryos. Whole-mount RNA in situ analysis of marker genes in normal and Lrp5+/-;Lrp6-/- mutant embryos between 7.5 dpc and 8.0 dpc. Anterior is towards the left in all panels. (A-D) Analysis of T expression. Control (A) and mutant (B) embryos showing expression of T in the primitive streak. Lines indicate level of transverse sections shown in C and D. Transverse section of a control embryo (C) showing T expression in the primitive streak (ps) and its rapid downregulation in nascent mesoderm migrating away from the streak (arrow). In the mutant embryo (D), T expression is seen within ectodermal cells and a few mesenchymal cells, but is downregulated in most of the mesenchymal cells that have accumulated in the abnormal primitive streak (arrowhead). Fewer mesodermal cells are seen migrating away from the streak (arrow). (E-H) Analysis of Lhx1 expression. Control (E) and mutant (F) embryos showing Lhx1 expression in mesendoderm. Line in F corresponds to level of transverse section in H; arrow in F indicates the allantois. Transverse section (G) through a slightly younger 7.5 dpc control embryo (inset) than pictured in E, showing Lhx1 expression in the primitive streak (ps) and in nascent mesoderm that has migrated laterally (arrow). Transverse section (H) of the mutant embryo shown in F showing Lhx1 expression in mesenchymal cells that have accumulated at the abnormal primitive streak (arrowhead). (I,J) Analysis of Ebaf expression. A control embryo (I) shows expression in the primitive streak and in wings of nascent mesoderm, whereas expression in the mutant embryo (J) is confined to cells accumulating at the posterior primitive streak. (K,L) Analysis of Tbx6 expression. A control embryo (K) shows expression in the primitive streak that is lost the mutant embryo (L). (M,N) Analysis of sprouty 2 (Spry2) expression. Expression is detected in primitive streak of both control (M) and mutant (N) embryos. All embryos were photographed at the same magnification, as were the sections.