CEDOC, Chronic Diseases Research Centre, NOVA Medical School. Faculdade de8 Ciências Médicas, Universidade Nova de Lisboa, Lisboa, Portugal.
Laboratorio Nacional de Microscopía Avanzada. Departamento de Genética del Desarrollo y Fisiología Molecular. Instituto de Biotecnología. Universidad Nacional Autónoma de México (UNAM), Cuernavaca, Mexico.
Elife. 2023 Jul 21;12:e83861. doi: 10.7554/eLife.83861.
Humans and other vertebrates define body axis left-right asymmetry in the early stages of embryo development. The mechanism behind left-right establishment is not fully understood. Symmetry breaking occurs in a dedicated organ called the left-right organizer (LRO) and involves motile cilia generating fluid-flow therein. However, it has been a matter of debate whether the process of symmetry breaking relies on a chemosensory or a mechanosensory mechanism (Shinohara et al., 2012). Novel tailored manipulations for LRO fluid extraction in living zebrafish embryos allowed us to pinpoint a physiological developmental period for breaking left-right symmetry during development. The shortest critical time-window was narrowed to one hour and characterized by a mild counterclockwise flow. The experimental challenge consisted in emptying the LRO of its fluid, abrogating simultaneously flow force and chemical determinants. Our findings revealed an unprecedented recovery capacity of the embryo to re-fil and re-circulate new LRO fluid. The embryos that later developed laterality problems were found to be those that had lower anterior angular velocity and thus less anterior-posterior heterogeneity. Next, aiming to test the presence of any secreted determinant, we replaced the extracted LRO fluid by a physiological buffer. Despite some transitory flow homogenization, laterality defects were absent unless viscosity was altered, demonstrating that symmetry breaking does not depend on the nature of the fluid content but is rather sensitive to fluid mechanics. Altogether, we conclude that the zebrafish LRO is more sensitive to fluid dynamics for symmetry breaking.
人类和其他脊椎动物在胚胎发育的早期阶段定义了身体轴的左右不对称性。左右建立的机制尚未完全了解。对称破坏发生在一个专门的器官，称为左右组织者（LRO），涉及运动纤毛在其中产生液流。然而，对称破坏的过程是依赖于化学感觉还是机械感觉机制一直存在争议（Shinohara 等人，2012 年）。在活体斑马鱼胚胎中对 LRO 流体提取进行定制操作的新方法使我们能够确定在发育过程中打破左右对称性的生理发育时期。最短的关键时间窗口被缩小到一个小时，其特征是轻微的逆时针流动。实验的挑战在于排空 LRO 的液体，同时消除流动力和化学决定因素。我们的发现揭示了胚胎前所未有的恢复能力，可以重新填充和重新循环新的 LRO 液体。后来出现左右不对称问题的胚胎被发现具有较低的前角速度，因此前后异质性较小。接下来，为了测试是否存在任何分泌的决定因素，我们用生理缓冲液代替提取的 LRO 液体。尽管存在一些短暂的流动均匀化，但如果不改变粘度，就不会出现左右不对称性缺陷，这表明对称破坏不依赖于流体内容物的性质，而是对流体力学敏感。总之，我们得出结论，斑马鱼 LRO 对对称破坏的流体动力学更敏感。
