Fig. 3. Interaction of xFRS2 with the Src family kinase Laloo. (A) Laloo enhances tyrosine phosphorylation of xFRS2. Effect of co-injection of xFGFR1 or Laloo Y492F (an active form) on tyrosine phosphorylation of xFRS2 was analyzed. Indicated sets of mRNA were injected at animal poles of 2-cell stage embryos and animal caps were dissected. The lysates of caps were immunoprecipitated (IP) with anti-myc antibody and immunoblotted with anti-phosphotyrosine antibody (upper) or anti-myc antibody (lower). (B) xFGFR1 and Laloo Y492F cooperate to induce tyrosine phosphorylation of xFRS2. The experiments were performed as described in (A). (C) xFRS2 binds to Laloo. Lysates of caps co-injected with the indicated combinations of mRNA encoding myc-tagged xFRS2 or HA-tagged Laloo were immunoprecipitated with anti-HA antibody. Co-immunoprecipitated xFRS2 was detected by blotting with anti-myc antibody (top). The amounts of the precipitated Laloo (middle) and the expression level of xFRS2 (bottom) were also determined. (D) Xbra induction by Laloo Y492F is dependent on xFRS2. Indicated combinations of mRNA encoding Laloo Y492F, WT xFRS2, or xFRS2-6F were co-injected into animal poles of 2-cell stage embryos. The animal cap assay and the RT–PCR analysis were performed as in Figure 2.