Fig. 2. SRp38 inhibits neural development but not initial induction of neural tissues. (A) In situ hybridization for neural specific nrp1, stage 21. Control embryo shows staining in the neural tube and eyes. Embryo injected in one cell at the two-cell stage with 500 pg SRp38 (right). Nrp-1 expression is lost at the site of injection (red arrowhead). (B) Simplified schematic of neural induction. Inhibition of bone morphogenetic protein (BMP) signaling by BMP antagonists, such as noggin, allows expression of Sox genes (Sox2 and Sox3) which then induce neural fates. (C) SRp38 does not block expression of Sox3 or Sox2 in whole embryos. Dorsal view of control embryos (left column) expressing Sox2 and Sox3 in the neural plate. Embryos injected in one cell at the two cell stage with 500 pg SRp38 (right column) also express Sox2 and Sox3 normally in the neural plate. Injected sides marked with red arrowhead. Lineage tracer in pink. (D) Ectodermal explant RT-PCR, stage 10.5. Noggin mRNA injection induces robust expression of Sox3 (lane 4). SRp38 co-expression is unable to block Sox3 expression (lane 6). (E) Ectodermal explant RT-PCR, stage 10.5. SRp38 mRNA injection does not induce expression of the BMP target Vex1. Embryos were injected with 500 pg (lane 4), 250 pg (lane 5) or 125 pg (lane 6). EF1 is a loading control and Xbra controls for mesodermal contamination. (F) In situ hybridization for nrp1 (neural). Noggin injected animal caps express nrp1 and co-injection of SRp38 prevents nrp1 expression.