Fig. 2. Tissue formation in embryos injected with POPK-1 MO. (A-C,E,G-M) Uninjected controls. (A'-C',E',G'-M') POPK-1 MO was injected into fertilized eggs after the completion of ooplasmic segregation. (D,F,I,L) Diagram of the vegetal hemisphere at the 110-cell stage, showing presumptive muscle, mesenchyme, notochord and endoderm blastomeres, respectively. Anterior is up. In (L), endoderm precursors are yellow, trunk lateral cell precursors are blue. B7.5 blastomeres give rise to muscle (red) and trunk ventral cells (purple). (A,A') Morphology. (B,B') Expression of muscle-specific acetylcholinesterase (AChE) in tailbud embryos. (C,C') Expression of myosin protein (Mu-2 antigen) in larvae. (E,E') Expression of myosin in embryos whose cleavages were arrested at the 110-cell stage. (G,G') Mesenchyme-specific Mch-3 antigen in cleavage-arrested embryos. (H,H') Notochord-specific Not-1 antigen. (J,J') Not-1 antigen in cleavage-arrested embryos. (K,K') Expression of alkaline phosphatase (ALP). (M,M') ALP in cleavage-arrested embryos. Ectopic ALP activity is observed in the posteriormost (B7.5) cells (arrowhead) in (M'). Scale bars: 100 µm.