The left–right (L–R) axis of most bilateral animals is established during gastrulation when a transient ciliated structure creates a directional flow of signaling molecules that establish asymmetric gene expression in the lateral plate mesoderm. However, in some animals, an earlier differential distribution of molecules and cell division patterns initiate or at least influence L–R patterning. Using single-cell high-resolution mass spectrometry, we previously reported a limited number of small molecule (metabolite) concentration differences between left and right dorsal-animal blastomeres of the eight-cell Xenopus embryo. Herein, we examined whether altering the distribution of some of these molecules influenced early events in L–R patterning. Using lineage tracing, we found that injecting right-enriched metabolites into the left cell caused its descendant cells to disperse in patterns that varied from those in control gastrulae; this did not occur when left-enriched metabolites were injected into the right cell. At later stages, injecting left-enriched metabolites into the right cell perturbed the expression of genes known to: (a) be required for the formation of the gastrocoel roof plate (foxj1); (b) lead to the asymmetric expression of Nodal (dand5/coco); or (c) result from asymmetrical nodal expression (pitx2). Despite these perturbations in gene expression, we did not observe heterotaxy in heart or gut looping at tadpole stages. These studies indicate that altering metabolite distribution at cleavage stages at the concentrations tested in this study impacts the earliest steps of L–R gene expression that then can be compensated for during organogenesis.

中文翻译：

---

在非洲爪蟾分裂阶段改变代谢物分布会影响左右基因表达不对称

大多数双侧动物的左右 (L-R) 轴是在原肠胚形成期间建立的，此时短暂的纤毛结构产生信号分子的定向流动，从而在侧板中胚层中建立不对称基因表达。然而，在某些动物中，分子和细胞分裂模式的早期差异分布启动或至少影响 L-R 模式。使用单细胞高分辨率质谱法，我们之前报道了八细胞非洲爪蟾左右背-动物卵裂球之间数量有限的小分子（代谢物）浓度差异胚胎。在这里，我们检查了改变其中一些分子的分布是否会影响 L-R 模式的早期事件。使用谱系追踪，我们发现将右侧富集的代谢物注入左侧细胞会导致其后代细胞以不同于对照原肠胚的模式分散。当左侧富集的代谢物被注入右侧细胞时，这并没有发生。在后期，将左侧富集的代谢物注入右侧细胞会扰乱已知基因的表达：（a）是形成胃腔顶板（foxj1）所必需的；(b) 导致 Nodal ( dand5/coco ) 的不对称表达；或 (c) 非对称节点表达式的结果 ( pitx2）。尽管基因表达存在这些扰动，但我们没有观察到蝌蚪阶段心脏或肠道循环的异向性。这些研究表明，在本研究中测试的浓度下改变裂解阶段的代谢物分布会影响 L-R 基因表达的最早步骤，然后可以在器官发生过程中得到补偿。