Department of Medical Biology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Department of Bioscience, Zoophysiology, Aarhus University, Aarhus, Denmark.
Sci Rep. 2017 Jul 27;7(1):6644. doi: 10.1038/s41598-017-06291-z.
Mammals evolved from reptile-like ancestors, and while the mammalian heart is driven by a distinct sinus node, a sinus node is not apparent in reptiles. We characterized the myocardial systemic venous pole, the sinus venosus, in reptiles to identify the dominant pacemaker and to assess whether the sinus venosus remodels and adopts an atrium-like phenotype as observed in mammals. Anolis lizards had an extensive sinus venosus of myocardium expressing Tbx18. A small sub-population of cells encircling the sinuatrial junction expressed Isl1, Bmp2, Tbx3, and Hcn4, homologues of genes marking the mammalian sinus node. Electrical mapping showed that hearts of Anolis lizards and Python snakes were driven from the sinuatrial junction. The electrical impulse was delayed between the sinus venosus and the right atrium, allowing the sinus venosus to contract and aid right atrial filling. In proximity of the systemic veins, the Anolis sinus venosus expressed markers of the atrial phenotype Nkx2-5 and Gja5. In conclusion, the reptile heart is driven by a pacemaker region with an expression signature similar to that of the immature sinus node of mammals. Unlike mammals, reptiles maintain a sinuatrial delay of the impulse, allowing the partly atrialized sinus venosus to function as a chamber.
哺乳动物由类似爬行动物的祖先进化而来，虽然哺乳动物的心脏由独特的窦房结驱动，但在爬行动物中并不明显。我们对爬行动物的心肌系统静脉极（窦房静脉）进行了特征描述，以确定主导起搏点，并评估窦房静脉是否会像在哺乳动物中那样发生重塑并采用类似心房的表型。变色龙蜥蜴的窦房静脉有大量表达 Tbx18 的心肌。一小部分细胞环绕着窦房结表达了 Isl1、Bmp2、Tbx3 和 Hcn4，这些基因是标记哺乳动物窦房结的同源基因。电映射显示，变色龙蜥蜴和蟒蛇的心脏由窦房结驱动。电脉冲在窦房静脉和右心房之间延迟，使窦房静脉收缩并有助于右心房充盈。在靠近体静脉的地方，变色龙的窦房静脉表达了心房表型的标志物 Nkx2-5 和 Gja5。总之，爬行动物的心脏由一个具有与哺乳动物未成熟窦房结相似表达特征的起搏区驱动。与哺乳动物不同的是，爬行动物的冲动在窦房结处存在延迟，使部分心房化的窦房静脉能够作为一个腔室发挥作用。
