Epidermal expression of apolipoprotein E gene during fin and scale development and fin regeneration in zebrafish

Apolipoprotein E (apoE) plays an important role in systemic and local lipid homeostasis, We have examined the expression of apoE during morphogenesis and regeneration of paired and unpaired fins and during scale development i n zebrafish (Danio rerio), In situ hybridization analysis revealed that, du ring embryogenesis, apoE is expressed in the epithelial cells of the median fin fold and of the pectoral fin buds. ApoE remains expressed in the elong ating fin folds throughout development of the fins. During the larval to ju venile transition, apoE transcripts were present in the distal, interray an d lateral epidermis of developing fins. Furthermore, as scale buds started to form, apoE was expressed in large scale domains which later, became rest ricted to the external posterior epidermal part of scales. A low level of t ranscripts could be observed at later developmental stages at these locatio ns probably because fins and scales continue to grow throughout the animal' s life. During regeneration of both pectoral and caudal fins, a marked incr ease in apoE expression is observed as early as 12 hours after amputation i n the wound epidermis, High levels of apoE transcripts are then localized p rimarily in the basal cell layer of the apical epidermis, The levels of apo E expression were maximum between the second to fourth days and then progre ssively declined to basal level by day 14, ApoE transcripts were also obser ved in putative macrophages infiltrated in the mesenchymal compartment of r egenerating fins a few hours after amputation. In conclusion, apoE is highl y expressed in the epidermis of developing fins and scales and during fin r egeneration while no expression can be detected in the skin of the trunk. A poE may play a specific role in fin and scale differentiation at sites wher e important epidermo-dermal interactions occur for the elaboration of the d ermal skeleton and/or for lipid uptake and redistribution within these rapi dly growing structures, Dev Dyn 1999;214:207-215. (C) 1999 Wiley-Liss, Inc.