Figure 3

(A) Schematic diagram of the time frame of SU5402 treatment of Xenopus embryos. (B) Morphology of embryos treated with SU5402 according to the designed time frame. Most of the embryos that were treated with SU5402 before stage 10.5 (groups A, B, and C) showed an expanded abdominal region. However, a curved back and shortened tail were seen in the group treated with SU5402 after stage 10.5 (group E). (C) Gene expression pattern of embryos treated with SU5402 according to the time frame. Expression of endodermin appeared to be normal in the case of FGF signal deprivation in embryos from fertilization to stage 10.5. However, its expression was abruptly decreased when the FGF signal was blocked after stage 10.5. This shows that FGF signal blockade before stage 10.5 is critically important for proper endoderm formation but persistent blocking of FGF signal after stage 10.5 inhibited proper endoderm formation. When the FGF signaling was blocked after stage 10.5, neural induction was inhibited as shown (Group D, E, F), and the expression of actin, a general mesodermal marker, was also reduced (group E, F). (D) The future endodermal region of the vegetal hemispheres was dissected from embryos at MBT and conjugated with animal cap explants. The conjugated explants were cultured with FGF signal blocking until stage 30. As shown in Group A, the expression of the general endodermal marker endodermin was increased by RT-PCR analysis but the expression of endodermal organ specific markers such as Xlhbox8 and IFABP were not observed when compared with conjugated explants cultured without SU5402. The RT-PCR results showed that the explants remained in the initial stage of the endodermalization instead of differentiating into the specific organ cells as shown at Group B.