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Fig. 5 Figure 5. ApoE expression during regeneration of the caudal fin. ApoE expression was determined A: 12 hr; B: 16 hr; C,D: 24 hr; F,H:2 days; E: 3 days; G,J: 4 days; L: 6 days; I: 14 days; K: 30 days after amputation. (A,C,E,G,I,K) whole-mount in situ hybridization. (B,D,F,J,L) proximo-distal and (H) transverse sections after in situ hybridization. The plane of amputation is indicated by a thick red arrow in A-G. A,C: apoE expression was observed as early as 12 hr after amputation at the apex of each truncated lepidotrichia. E,G: a strong expression was detected in the apical epidermis of each fin ray during the first 4 to 6 days of regeneration. I: 14 days after amputation, apoE expression has considerably decreased. K: 30 days after amputation, apoE expression levels are comparable to control non-amputated fin. A thin red arrow indicates a formed bifurcation in I and apoE expression along the lateral side of the fin in K. B: frozen section along the proximo-distal axis of a fin 16 hr after amputation shows that apoE is expressed in the epidermal cells covering the wound as well as in putative macrophages (thin red arrow). F: putative macrophages expressing apoE are also observed 2 days after amputation. D: 24 hr after amputation, apoE is expressed in the basal layer of the epidermis. F,H,J,L: Throughout the regeneration process, apoE is abundantly expressed in the basal layer of the apical epidermis and to a lesser extend in the intermediate cell layers. ApoE transcripts are never detected in the most superficial epidermal layer. H: transverse section shows that apoE is expressed at a low level in the basal epidermal layer of the inter-ray tissue. ae, apical epidermis; b, blastema; be, basal layer of the epidermis; l, lepidotrichia ; we, wound epidermis. A,C,E,G,I,K scale bar = 200 m ; B,D,F,H,J,L scale bar = 20 m.