Fig. 5. Gene silencing of TSK results in the inhibition of organizer formation. (A) Transplantation scheme of siRNA experiments. Two chick embryos were electroporated with siRNA at stage 3⁺ and the excised MPSs were implanted into the lateral Hensen's node of the host embryo. (B) The embryo at stage 3⁺ was electroporated with control1, TSKA or TSKs siRNA. Hensen's node and the anterior fourth of the primitive streak were surgically removed. After 6 hours incubation, the level of VG1 or TSKB mRNA in the MPS was determined by RT-PCR. (C-J) After carrying out experiments according to the diagram in A, the ectopic induction of chordin (C-F) or goosecoid (G-J) was examined by in situ hybridization. (D,E) In the case of control1 and TSKA siRNAs, the MPS induced ectopic expression of chordin in 17/44 (39%) and 12/32 (38%), respectively, which are similar to embryos without electroporation (C) [20/50 (40%)]. (F) In the case of TSKs siRNA, the MPS induced ectopic expression of chordin in 8/40 (20%) embryos. (H,I) In the case of control1 and TSKA siRNAs, the MPS induced ectopic expression of goosecoid in 12/42 (29%) and 12/44 (27%), respectively, which are similar to embryos without electroporation (G) [12/40 (30%)]. (J) In the case of TSKs siRNA, the MPS induced ectopic expression of chordin in 7/53 (13%) embryos.