Fibroblasts at the horizontal myoseptum express Engrailed proteins. a-i) HM region of 48hpf embryos that were stained with anti-Engrailed (red) and anti-GFP (green) antibodies. a-c) All cells expressing the vegfc:Gal4FF; UAS: GFP reporter at the HM do co-express Engrailed proteins. d-f) fpdg-fra:mCitrine positive fibroblasts at the HM are also positive for Engrailed. g-i) Partial z-projections of the HM region reveal a co-expression of the adamts3 reporter and Engrailed proteins within fibroblasts. j, m) Two additional examples of genes whose transcripts are highly enriched within fibroblast cluster 2 are nuak1b and tgbl1 (see Supplementary Tables 1-3). The mRNA of both genes (k, l, n, o) can be detected specifically at the midline by ISH at 48hpf, thereby validating the notion that the cells in cluster 2 represent the fibroblast subpopulation located at the HM. Scale bars in a-i: 25 μm; k, l, n and o: 50 μm. hpf: hours post fertilization, HM: horizontal myoseptum
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