Afzelius B A
The Wenner-Gren Institute, Stockholm University, Sweden.
Int J Dev Biol. 1999 Jul;43(4):283-6.
Evidence is given for the opinion that cilia in the early embryo, by their work, determine the laterality of the body; without ciliary work body laterality would be randomized. More exactly, monocilia in the primitive node are responsible for this determination. They have been described as being of the 9+0 type, but with dynein arms and with a gyrating movement. The orientation of the monocilia on the epithelium is of no importance but the direction of their gyration is, as may also be the shape of the node. The chirality of the cilia is thus reflected directly in the asymmetry of the body. The dynein arms go clockwise as seen from the base to tip and the ciliary rotation is in the same direction. The resulting waterflow is towards the left and so is the movement of the forming heart. In most subgroups of the immotile-cilia syndrome this mechanism does not work and equally many individuals will be born with situs inversus as with situs solitus. An exception is the immotile-cilia subgroup, named 'microtubule transposition', which is characterized by all cilia having a 9+0 structure throughout most of their length.
早期胚胎中的纤毛通过其活动决定身体的左右不对称性；如果没有纤毛的活动，身体的左右不对称性将是随机的。更确切地说，原始节点中的单纤毛负责这种决定。它们被描述为9+0类型，但具有动力蛋白臂并进行旋转运动。上皮细胞上单纤毛的方向并不重要，但其旋转方向很重要，节点的形状可能也很重要。因此，纤毛的手性直接反映在身体的不对称性上。从基部到顶端看，动力蛋白臂按顺时针方向移动，纤毛的旋转方向相同。由此产生的水流向左，正在形成的心脏的运动方向也向左。在大多数不动纤毛综合征亚组中，这种机制不起作用，出生时内脏反位和内脏正位的个体数量相同。一个例外是不动纤毛亚组，称为“微管转位”，其特征是所有纤毛在大部分长度上都具有9+0结构。
