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Fig. 5 Expression of you Examined by In Situ Hybridization. (A and B) Maternal you transcripts were evident in cleavage-stage embryos (A) (16-cell; 1.5 hpf), and you mRNA was widely expressed into the gastrula period (B) (shield stage; 6 hpf). In addition, you mRNA was detectable by RT-PCR at 2 hpf, prior to the zebrafish midblastula transition. (C) Toward the end of gastrulation, you transcripts began to be restricted, so that at the bud stage (10 hpf), you expression was evident in the eye field (white arrowhead), in the developing midbrain and hindbrain (black arrowheads), and in posterior paraxial stripes (arrow). (D) During early somitogenesis (12 hpf), you expression was observed in the eye field (white arrowhead), in stripes in the midbrain and the MHB (black arrowheads), in a complex pattern in the hindbrain (white arrow), and in paraxial stripes along the developing trunk and tail bud (black arrow). (E and F) At 24 hpf, you transcripts were observed dorsal to the hypothalamus (black arrow), at the boundary between the telencephalon and the diencephalon (white arrow), in the ventral tectum (white arrowhead), in the region of the presumptive cerebellum (asterisk), and dorsally along the length of the spinal cord. Additional expression of you at this stage and later was observed in the ventral tail and at the urogenital opening (arrowheads; data not shown). (G and H) At 48 hpf, you transcripts were highly expressed in the cerebellum (black arrow), and were also present in the rhombic lip (white arrowhead), and continuing along the length of the anterior–posterior axis in the dorsal spinal cord (black arrowhead; data not shown). Orientation of images: (A) lateral view; (B) lateral view, dorsal to the right; (C, D, F, and G) dorsal views, anterior to the left; (E and H) lateral views, anterior to the left.