Temporal and spatial cycle of her1 expression in the presomitic mesoderm between 5- and 7-somite stages. For staging criteria, see text. The embryos which had been hybridized with her1 and mesp-a probes were first processed for her1 staining (Fast Red), followed by mesp-a staining (BM purple). A pair of photographs in upper (A-G; rhodamine filter) and lower (A′-G′; bright field) panels were taken of the same flat mounted samples. Under the rhodamine filter, only the her1 signal is sensitively detected. Simplified diagrams illustrating expression profile of her1 (red) and mesp-a (blue) are shown at the bottom (A′′- G′′). Solid lines represent formed somites while dotted lines represent successively forming somites. The her1 expression domain appears around the tailbud, and moves anteriorly until it finally overlaps with the most anterior stripe of mesp-a. Both stripes disappear near the point of furrow formation. The posterior tip of the tailbud is always positive for her1 transcripts. A stripe of her1 appears every 30 minutes in the tailbud region, and persists for about 1.5 hours (three somite cycles in zebrafish). Since we cannot judge accurately the lengths of individual sub-stages, we make no claim that the diagrams at the bottom are evenly spaced in time. Bars, 100 μm.
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