During somite segmentation, the expression of clock genes such as Hes7 oscillates synchronously in the presomitic mesoderm (PSM). This synchronous oscillation slows down in the anterior PSM, leading to wave-like propagating patterns from the posterior to anterior PSM. Such dynamic expression depends on Notch signaling and is critical for somite formation. However, it remains to be determined how slowing oscillations in the anterior PSM are controlled, and whether the expression of the Notch ligand Delta-like1 (Dll1) oscillates on the surface of individual PSM cells, as postulated to be responsible for synchronous oscillation. Here, by using Dll1 fluorescent reporter mice, we performed live-imaging of Dll1 expression in PSM cells and found the oscillatory expression of Dll1 protein on the cell surface regions. Furthermore, a comparison of live-imaging of Dll1 and Hes7 oscillations revealed that the delay from Dll1 peaks to Hes7 peaks increased in the anterior PSM, suggesting that the Hes7 response to Dll1 becomes slower in the anterior PSM. These results raise the possibility that Dll1 protein oscillations on the cell surface regulate synchronous Hes7 oscillations, and that the slower response of Hes7 to Dll1 leads to slower oscillations in the anterior PSM.

在体节分割过程中，Hes7等时钟基因的表达在先兆中胚层（PSM）中同步振荡。该同步振荡在前PSM处减慢，导致从后PSM到前PSM呈波状传播。这种动态表达取决于Notch信号传导，并且对于形成体节至关重要。然而，尚待确定如何控制前PSM中的减慢振荡，以及Notch配体Delta-like1（Dll1）的表达是否在单个PSM细胞的表面上振荡，这被认为是造成同步振荡的原因。在这里，通过使用Dll1荧光报告基因小鼠，我们对PSM细胞中Dll1表达进行了实时成像，并在细胞表面区域发现了Dll1蛋白的振荡表达。此外，比较了Dll1和Hes7的实时成像振荡表明，前PSM中从Dll1峰到Hes7峰的延迟增加，这表明前PSM中对Dll1的Hes7反应变慢。这些结果提高了细胞表面Dll1蛋白振荡调节同步Hes7振荡的可能性，并且Hes7对Dll1的响应变慢导致前PSM振荡变慢。