Fig. 7. Wild-type and mutant XSOX3 effects on endogenous Xnr5. (A) Fertilized eggs were injected with RNAs encoding wild-type (wt), m7 (m7) or m8 (m8) V5H₆-tagged forms of XSOX3. All three polypeptides accumulated to similar levels in stage-8 embryonic lysates (lysates). The binding wild-type and m7 polypeptides to both wild-type Xnr5 (Xn) and DC5 (DC) sequences (fishing) were much stronger than the binding of m8 under these conditions. (B) Xnr5 is normally expressed in the vegetal region of the embryo in response to the maternal factor VegT. Embryos were injected in the animal hemisphere with VegT RNA (1 ng) at the one-cell stage, either alone or together with RNA encoding XSOX3 (1 ng). At stage 8, animal caps were prepared. After a 2 hour incubation, they were homogenized and analysed by RT-PCR. Animal caps from uninjected embryos (AC/Un) did not express Xnr5 RNA; Xnr5 RNA was expressed in animal caps derived from embryos injected with VegT RNA (AC/VegT). Co-injection of VegT and wild-type (AC/VegT/+Sx3) or m7 (AC/VegT/+m7) XSOX3 RNAs suppressed the accumulation of Xnr5 RNA, whereas m8 RNA (AC/VegT/+m8) had no effect on Xnr5 RNA accumulation in response to VegT.