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Fig. 8 nrd and Islet-1 are coexpressed in several cell lineages in the embryonic zebrafish. Bar – 100μm. A, B: nrd mRNA and Islet-1 are often localized within the same cells in the 17 hpf embryos. Embryos were stained by whole mount in situ hybridization for nrd (dark staining of the cytoplasm with alkaline phosphatase) and by whole mount immunohistochemistry for Islet-1 (fluorescence detects fluorescein in the cell nuclei). A: an optical section on the level of MN. nrd expression in RB cells is seen as dark spots in the dorsal part of the spinal cord - white arrow. Islet-1 staining in MN is shadowed by the dark product of alkaline phosphatase - arrowheads. B: an optical section on the level of RB cells. There are two populations of Islet-1 - positive cells in the dorsal spinal cord. The first cell population coexpresses nrd and Islet-1. Islet-1 fluorescent signals are shadowed by the dark product of alkaline phosphatase used to detect nrd (filled stars). The second cell population is characterized by bright Islet-1-coupled fluorescence. There are no detectable nrd transcripts in these cells (open stars). Note that RB cells of both populations can be located on the same A-P level, suggesting that nrd expression could be more limited compared to that of Islet-1. C: nrd expression at 33 hpf, ventral view. Star - telencephalon and olfactory placode, arrowheads - ventral retina, asterisk- ventral forebrain. D: islet-1 expression at 36 hpf, star - telencephalon and olfactory placode, arrowheads - retina, asterisk-ventral forebrain; mb - midbrain; hb - hindbrain; tg - trigeminal ganglia. E: an isolated eye at 33 hpf after hybridisation with nrd. Note nrd staining in the ventral retina (arrowheads) and olfactory placode (arrow). F: an isolated eye at 33 hpf after hybridisation with islet-1. Note islet-1 transcripts in the retina and olfactory placode. E, F: photomontage presents olfactory placode connected to the anterior portion of the eye.