White J A, Boffa M B, Jones B, Petkovich M
Department of Pathology, Queen's University, Kingston, Ontario, Canada.
Development. 1994 Jul;120(7):1861-72. doi: 10.1242/dev.120.7.1861.
Retinoic acid (RA) is an important signalling molecule in vertebrate pattern formation both in developing and regenerating tissues. The effects of RA are due largely to regulation of gene transcription, mediated by retinoic acid receptors (RAR-alpha, RAR-beta, RAR-gamma) and retinoid X receptors (RXR-alpha, RXR-beta, RXR-gamma). We have been using zebrafish as a model of regeneration to study the role of retinoic acid and its receptors in vertebrate pattern formation. In this report, we describe the molecular cloning and characterization of one of the zebrafish RARs that is the predominant receptor in the regenerating caudal fin and corresponds most closely to the RAR-gamma subtype isolated from mouse and human and to RAR-delta from newt. Zebrafish RAR-gamma (zfRAR-gamma) exhibits both structural and functional conservation with its mammalian counterparts. Studies utilizing both normal and regenerating caudal fins of the zebrafish have indicated that it is the RAR-gamma subtype, compared to RAR-alpha or RAR-beta, which is expressed at the highest levels in the tail fin. To localize the expression pattern of RAR-gamma during fin regeneration, we have carried out whole-mount in situ hybridization. ZfRAR-gamma transcripts, during fin regeneration, are localized in the blastemal tissue formed at the distal ends of the bony rays following amputation. Treatment of fish with RA during fin regeneration induces a number of striking morphological effects on the regenerate. When amputations are performed distal to the branch points or dichotomies, where a single ray bifurcates to extend two individual 'daughter' rays, RA treatment causes a dichotomy reduction where the two 'daughter' rays fuse to once again form a single ray. The single ray subsequently bifurcates in a comparatively normal manner. Our data suggest that exogenous RA can respecify pattern in the regenerating caudal fin and identifies the blastemae as possible RA target tissues.
视黄酸（RA）是脊椎动物在发育和再生组织模式形成过程中的一种重要信号分子。RA的作用主要归因于由视黄酸受体（RAR-α、RAR-β、RAR-γ）和类视黄醇X受体（RXR-α、RXR-β、RXR-γ）介导的基因转录调控。我们一直将斑马鱼作为再生模型，研究视黄酸及其受体在脊椎动物模式形成中的作用。在本报告中，我们描述了斑马鱼RAR之一的分子克隆和特性，该RAR是再生尾鳍中的主要受体，与从小鼠和人类中分离出的RAR-γ亚型以及蝾螈的RAR-δ最为接近。斑马鱼RAR-γ（zfRAR-γ）与其哺乳动物对应物在结构和功能上均具有保守性。利用斑马鱼正常和再生尾鳍进行的研究表明，与RAR-α或RAR-β相比，RAR-γ亚型在尾鳍中的表达水平最高。为了定位鳍再生过程中RAR-γ的表达模式，我们进行了全胚胎原位杂交。在鳍再生过程中，zfRAR-γ转录本定位在截肢后骨射线远端形成的芽基组织中。鳍再生期间用RA处理鱼会对再生体产生许多显著的形态学影响。当在分支点或二分点远端进行截肢时（单个射线在此处分叉形成两条单独的“子”射线），RA处理会导致二分减少，两条“子”射线融合再次形成一条单射线。这条单射线随后以相对正常的方式分叉。我们的数据表明，外源性RA可以重新指定再生尾鳍中的模式，并将芽基确定为可能的RA靶组织。
