Fig. 3

Tissue-specific enhancer activity in the lamprey NC. a, d The SoxE1 a and Tfap2B d loci of the sea lamprey germline genome, with merged replicate ATAC-seq coverage tracks from the sea lamprey (Pm) and brook lamprey (Lp) at each developmental stage. Bars below coverage plots indicate peak regions identified with Macs2. The black box indicates the region tested in enhancer-reporter assays. b GFP reporter expression in lamprey embryos injected with the SoxE1 enhancer-reporter construct at the one-cell stage and allowed to grow to indicated stages (observed in 195 out of 1337 injected embryos). In transverse section (row 2, panels 2–6) GFP⁺ cells are visible delaminating from the neural tube at T22 (n = 2), migrating between the neural tube and otic vesicle at T23 (n = 2) and contributing to the branchial arch cartilage at T26 (n = 3). Coloured stars indicate panels showing the same embryo at successive developmental stages. Dashed boxed regions indicate regions magnified in adjacent panels. c Overlap of GFP reporter expression with native SoxE1 expression (magenta) in the delaminating and migrating NC at T23L (arrowheads; n = 4) and in the branchial ach cartilage at T25 (n = 2). e GFP reporter expression in lamprey embryos injected with the Tfap2B enhancer-reporter construct at one-cell stage and allowed to grow to indicated stages (observed in 25 out of 340 injected embryos). In transverse section at T26 (panel 5), GFP⁺ cells are visible in the branchial arch cartilage (n = 3). Bac, branchial arch cartilage; L, late; Nt, neural tube; Obc, orobranchial cavity; Ov, otic vesicle. Scale bars for wholemounts: 200 μm. Scale bars for sections: 25 μm