Fig. 3.

In situ hybridization analyses of Ext2^−/− mutants. Hybridization was performed with ³⁵S-labeled riboprobes and sections were counterstained with Hematoxylin (A-J) or Hoechst (K-T). In all sections, embryos are viewed laterally and the anterior side of the embryo is towards the left. (A-H) Embryos collected at E6.5. (A,B) H19, a marker for extra-embryonic tissues shows the presence of extra-embryonic ectoderm, endoderm, ectoplacental cone and trophoblast giant cells in Ext2^−/−. The broken line indicates the difference in development of the extra-embryonic parts of the egg cylinder. (C,D) Apoe, a marker for visceral endoderm, is expressed in Ext2^−/− embryos. (E,F) Fgf8, a marker for primitive streak formation, is detected in wild-type embryos and in Ext2^−/−. (G,H) Brachyury (T), another marker for primitive streak and mesodermal cells, is present in wild-type embryos, but not in Ext2 mutants. Embryos collected at E7.5 (I-T). (J) Class 2 mutant; (L,N,P,R,S,T) class 3 mutants; (I,K,M,O,Q) wild type. Brachyury is expressed in class 2 mutants (J) and in class 3 mutants (L,N,P,R,S,T). (M,N) H19 was used as a probe to show the boundaries between embryonic and extra-embryonic regions of the wild-type embryos and Ext2^−/− mutants. (O,P) Lim1 is expressed in wild-type embryos at low levels in primitive streak and at higher levels in mesodermal cells migrating away from the streak. Arrowheads indicate several cells expressing Lim1 in the Ext2^−/− mutants. (Q,R) Snai1 expression is shown in the primitive streak and nascent mesoderm of wild-type embryos (Q) but is absent in Ext2^−/− embryos (R). (S) Otx2 and (T) Hesx1 mRNAs are detected in the anterior cell mass of class 3 Ext2 mutants. ecp, ectoplacental cone; eec, embryonic ectoderm; ps, primitive streak; tgc, trophoblast giant cells; ven, visceral endoderm. Scale bars: 50 μm in A-H; 100 μm in I-T.