Functional enhancers in the <i>HDAC9-TWIST1</i> locus characterized using zebrafish and mice.

(A) A scheme of the HDAC9-TWIST1 locus. UCSC genome browser track represents genes and black bars represents enhancer candidate sequences. (B) Zebrafish whole-mount in situ hybridization of twist1b shows head, pectoral fin and branchial arch expression at 72 hpf. (C) Mouse whole-mount in situ hybridization of Twist1 shows limb and branchial arch expression along the anterior-posterior axes at E11.5. (D) Mouse whole-mount in situ hybridization of Hdac9 shows no expression in the limb and branchial arch at E11.5. (E–H) Tissue-specific enhancers in zebrafish embryos at 72 hpf. Tissue-specific GFP expression is indicated by red arrows: (E) branchial arch; (F) pectoral fin and branchial arch; (G) pectoral fin and branchial arch; (H) pectoral fin, otic vesicle and branchial arch. (I-N) Tissue-specific enhancers in mouse E11.5 embryos. Tissue-specific LacZ expression is indicated by red arrows: (I, I') pharyngeal arch 2; (J, J') whole limb bud; (K, K') posterior limb bud and branchial arch (known as HDAC eExon19); (L, L') dorsal and anterior limb bud (known as HDAC eExon18); (M, M') the base of the limb bud; (N, N') distal and posterior limb bud. The dashed boxes highlight tissue-specific expression. The numbers in the bottom left of the embryo pictures indicate the number of embryos showing this expression pattern from the total number of LacZ-stained embryos. Abbreviations: Pectoral fin (PF), branchial arch (BA), otic vesicle (OV), forelimb (FL), hindlimb (HL), mandibula (Md), pharyngeal arch 2 (PA2). Images K and L were taken with permission from Birnbaum et al. [4].