Fig. 5. The Spätzle processing reaction in wild-type and Egfr¹ embryos. (A) Extracts were prepared from 0-4 hour embryos laid by wild-type, spz^-, ea^-, and Toll^- females. Proteins were separated on a 12.5% polyacrylamide gel and transferred to PVDF. The mobility of molecular weight markers is shown on left. The immunoblot was probed with antibodies directed against the N-terminal half of Spätzle protein. Full-length forms of Spätzle are marked by the bracket. Prominent proteolytically processed forms of N-terminal Spätzle, present in wild-type embryos and absent in embryos laid by ea^- females, are indicated by arrows (migrating as 23 and 27 kDa proteins). (B) An immunoblot with the same samples as in A was probed with antibodies directed against the C-terminal half of Spätzle protein. The arrow marks the proteolytically processed form of C-terminal Spätzle (migrating as a 21 kDa protein). (C) On the left, extracts were prepared from sorted stage 4-5 embryos laid by wild-type or Egfr¹ females. On the right, conventional extracts were prepared from 0-4 hour embryos laid by wild-type, spz^-, and Toll^- females. The immunoblot was probed with antibodies directed against the C-terminal half of Spätzle protein. (D) Cuticle of embryo laid by wild-type female and injected with N-spz RNA is strongly dorsalized. The bright outline is the vitelline membrane. (E) Cuticle of dorsalized embryo laid by spz^- female.

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