Calcineurin Controls Proximodistal Blastema Polarity in Zebrafish Fin Regeneration

Planarian flatworms regenerate their heads and tails from anterior or posterior wounds and this blastema regeneration polarity is controlled by Wnt/β-catenin signaling. It is well known that a regeneration blastema of appendages of vertebrates such as fish and amphibians grows distally. However, it remains unclear whether a regeneration blastema in vertebrate appendages can grow proximally. Here, we show that a regeneration blastema in zebrafish fins can grow proximally along the proximodistal axis by calcineurin inhibition. We used fin excavation in adult zebrafish to observe the unidirectional regeneration, from the anterior cut edge (ACE) to the posterior cut edge (PCE) of the cavity and this unidirectional regeneration polarity occurs as the PCE fails to build blastemas. Furthermore, we found that calcineurin activities in the ACE were greater than in the PCE. Calcineurin inhibition induced the PCE blastemas, and calcineurin hyperactivation suppressed fin regeneration. Collectively, these findings identify calcineurin as a molecular switch to specify the PCE blastema of the proximodistal axis and regeneration polarity in zebrafish fin. Zebrafish Fin mRNA profiles of the anterior cut edge (ACE) and the posterior cut edge (PCE) at 24, 48, and 72 hpa (hours post amputation)

扁形涡虫（Planarian flatworms）可通过前部或后部伤口实现头部与尾部的再生，其芽基（blastema）再生极性由Wnt/β-连环蛋白信号通路调控。已有研究证实，鱼类、两栖类等脊椎动物的附肢再生芽基会沿远端方向生长，但目前尚不明确脊椎动物附肢的再生芽基是否可实现近端生长。本研究表明，通过抑制钙调神经磷酸酶（calcineurin），斑马鱼鳍的再生芽基可沿近远轴向近端延伸。我们对成年斑马鱼实施鳍切除术，观察到切除后形成的空腔呈现单向再生模式：再生从空腔的前部切割边缘（anterior cut edge，简称ACE）向后部切割边缘（posterior cut edge，简称PCE）进行，该单向再生极性的成因在于后部切割边缘无法形成芽基。进一步实验发现，前部切割边缘的钙调神经磷酸酶活性显著高于后部切割边缘；抑制钙调神经磷酸酶可诱导后部切割边缘形成芽基，而钙调神经磷酸酶的过度激活则会抑制鳍的再生。综上，本研究证实钙调神经磷酸酶可作为分子开关，调控斑马鱼鳍近远轴后部切割边缘芽基的形成与再生极性。本数据集涵盖斑马鱼鳍在截肢后24、48、72小时（hours post amputation，简称hpa）时，前部切割边缘与后部切割边缘的mRNA表达谱。