Department of Biology/Chemistry, Zoology & Developmental Biology, Osnabrück University, 49076 Osnabrück, Germany.
Center of Cellular Nanoanalytics (CellNanOs), Osnabrück University, 49076 Osnabrück, Germany.
J Exp Biol. 2023 Jul 1;226(13). doi: 10.1242/jeb.245839. Epub 2023 Jul 5.
Drosophila, like all insects, has an open circulatory system for the distribution of haemolymph and its components. The circulation of the haemolymph is essentially driven by the pumping activity of the linear heart. The heart is constructed as a tube into which the haemolymph is sucked and pumped forward by rhythmic contractions running from the posterior to the anterior, where it leaves the heart tube. The heart harbours cardiac valves to regulate flow directionality, with a single heart valve differentiating during larval development to separate the heart tube into two chambers. During metamorphosis, the heart is partially restructured, with the linear heart tube with one terminal wide-lumen heart chamber being converted into a linear four-chambered heart tube with three valves. As in all metazoan circulatory systems, the cardiac valves play an essential role in regulating the direction of blood flow. We provide evidence that the valves in adult flies arise via transdifferentiation, converting lumen-forming contractile cardiomyocytes into differently structured valve cells. Interestingly, adult cardiac valves exhibit a similar morphology to their larval counterparts, but act differently upon heart beating. Applying calcium imaging in living specimens to analyse activity in valve cells, we show that adult cardiac valves operate owing to muscle contraction. However, valve cell shape dynamics are altered compared with larval valves, which led us to propose our current model of the opening and closing mechanisms in the fly heart.
果蝇与所有昆虫一样，具有用于血液及其成分分配的开放式循环系统。血液的循环主要是由线性心脏的泵送活动驱动的。心脏构造为一个管腔，血液通过从后到前的有节奏收缩被吸入并向前泵送，然后离开心脏管腔。心脏具有心脏瓣膜来调节血流方向，在幼虫发育过程中会分化出一个单一的心脏瓣膜，将心脏管腔分隔成两个腔室。在变态过程中，心脏会部分重构，线性的心脏管腔及其单一的宽腔心腔会被转化为具有三个瓣膜的线性四腔心管腔。与所有后生动物循环系统一样，心脏瓣膜在调节血流方向方面起着至关重要的作用。我们提供的证据表明，成年果蝇的瓣膜是通过转分化产生的，即将形成腔的收缩型心肌细胞转化为具有不同结构的瓣膜细胞。有趣的是，成年心脏瓣膜的形态与幼虫瓣膜相似，但在心脏跳动时的作用方式不同。我们通过对活体标本进行钙成像分析来研究瓣膜细胞的活性，结果表明，成年心脏瓣膜的工作原理是基于肌肉收缩。然而，与幼虫瓣膜相比，瓣膜细胞的形状动力学发生了改变，这促使我们提出了目前关于果蝇心脏瓣膜开闭机制的模型。
