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Fig. 3 seahorse mRNA is expressed in tissues that possess motile cilia. (A) RT-PCR of sea mRNA (503 bp) in cDNA libraries at the one- to two-cell, 256-cell, 1024-cell, sphere and 18-somite stages. sea mRNA was maternally expressed as zygotic transcription initiates after the 1024-cell stage. (B-J) Expression of sea was detected by RNA in situ hybridization in dorsal forerunner cells at 90% epiboly (B), in KV at 3 somites (C), and in the floor plate at 22 somites (D, arrowheads), 24 hpf (E,F arrowheads; G, bracket) and 48 hpf (J, arrowhead). Expression was detected in the pronephric tubules at 22 somites (D, arrows), 24 hpf (E,F, arrows), 36 hpf (H, arrow) and at 48 hpf (I,J, arrow). Open arrows in G and I indicate sea expression in the chordoneural hinge. Double-headed arrows in D,F and G span the width of the notochord, sea mRNA is not detected. Inset in F is a higher magnification image of the patchy pronephric expression that resembles expression of genes in multiciliated cells (Liu et al., 2007; Ma and Jiang, 2007).