Celsr/Flamingo has a potential pro-region mediating dimer formation. (A) The comparison of the region N-terminal to the Cadherin repeats indicates a Furin-like protease cleavage site (arrowhead) conserved amongst Drosophila Fmi and vertebrate Celsr. (B) The design for Celsr-Activin fusion proteins. A potential pro-region of zebrafish Celsr2 (blue), including the Furin-like cleavage site, is fused to the mature region of mouse Activin A (pink) to generate FmiP-Act (see Materials and methods for details). The potential cleavage site is mutated in alanine. (C-N) Wild-type embryos were injected with 5 pg mouse activin RNA (F-H), 50 pg FmiP-Act RNA (I-K), 100 pg FmiP-Act-RA RNA(L-N) or left uninjected (C-E), and fixed at 50% epiboly to examine expression of the mesoderm or endoderm markers ntl (C,F,I,L), gsc (D,G,J,M) or bon (E,H,K,N).
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