Microstructures regulate distant cellular interactions during heart formation

Communication between endocardium and myocardium, separated by cardiac jelly, is essential for cardiac morphogenesis. How membrane-localized receptors and ligands achieve interaction across the cardiac jelly is not understood. Utilizing a number of approaches, including genetic labeling of cell-cell contacts, we found that myocardium and endocardium interact directly via microstructures, termed Tunneling Nanotube-Like microstructures (TNTLs). TNTLs extend from cardiomyocytes to directly contact endocardial cells (ECs). TNTLs transport cytoplasmic proteins, transduce signals between cardiomyocytes and ECs, and initiate myocardial growth toward the lumen to form ventricular trabeculae-like structures. Loss of TNTLs disturbs signaling interactions and, subsequently, ventricular patterning. Whole hearts from E9.5 control and myocardial Cdc42 knockout (MCKO) are analyzed, each set contains three hearts.由心胶质（cardiac jelly）分隔的心内膜与心肌之间的相互通讯，对心脏形态发生过程至关重要。目前，膜定位受体与配体如何跨越心胶质完成相互作用这一问题尚未阐明。我们采用包括细胞-细胞接触遗传标记在内的多种实验手段，发现心肌与心内膜可通过一类被称为隧道纳米管样微结构（Tunneling Nanotube-Like microstructures，TNTLs）的微观结构实现直接相互作用。TNTLs由心肌细胞延伸而出，可直接与心内膜细胞（endocardial cells，ECs）接触。该结构能够转运细胞质蛋白，在心肌细胞与心内膜细胞之间传递信号，并启动心肌向管腔方向生长以形成心室小梁样结构。TNTLs的缺失会扰乱二者的信号相互作用，进而引发心室模式构建异常。我们对E9.5期对照小鼠及心肌细胞Cdc42基因敲除（myocardial Cdc42 knockout，MCKO）小鼠的完整心脏进行了分析，每组各包含3个心脏样本。