Oates Andrew C, Mueller Claudia, Ho Robert K
Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany.
Dev Biol. 2005 Apr 1;280(1):133-49. doi: 10.1016/j.ydbio.2005.01.010.
Segmentation of paraxial mesoderm in vertebrates is regulated by a genetic oscillator that manifests as a series of wavelike or cyclic gene expression domains in the embryo. In zebrafish, this oscillator involves members of the Delta/Notch intercellular signaling pathway, and its down-stream targets, the Her family of transcriptional repressors. Loss of function of any one of the genes of this system, such as her7, gives rise to segmentation defects in the posterior trunk and tail, concomitant with a disruption of cyclic expression domains, indicating that the oscillator is required for posterior segmentation. Control of segmentation in the anterior trunk, and its relationship to that of the posterior is, however, not yet well understood. A combined loss of the cyclic Her genes her1 and her7 disrupts segmentation of both anterior and posterior paraxial mesoderm, indicating that her genes function redundantly in anterior segmentation. To test whether this anterior redundancy is specific to the her gene family, or alternatively is a more global feature of the segmentation oscillator, we looked at anterior segmentation after morpholino knock down of the cyclic cell-surface Notch ligand deltaC (dlc), either alone or in combination with her7, or other Delta/Notch pathway genes. We find that dlc is required for coherence of wavelike expression domains of cyclic genes her1 and her7 and maintenance of their expression levels, as well as for cyclic transcription of dlc itself, confirming that dlc is a component of the segmentation oscillator. Dose dependent, posteriorly-restricted segmentation defects were seen in the dlc knock down, and in combination with the deltaD or notch1a mutants. However, combined reduction of function of dlc and her7 results in defective segmentation of both anterior and posterior paraxial mesoderm, and a failure of cyclic expression domains to initiate, similar to loss of both her genes. Thus, anterior segmentation requires the functions of both her and delta family members in a parallel manner, suggesting that the segmentation oscillator operates in paraxial mesoderm along the entire vertebrate axis.
脊椎动物中轴旁中胚层的分割受一种基因振荡器调控，该振荡器在胚胎中表现为一系列波状或周期性的基因表达域。在斑马鱼中，这种振荡器涉及Delta/Notch细胞间信号通路的成员及其下游靶点——Her家族转录抑制因子。该系统中任何一个基因（如her7）功能丧失都会导致后躯干和尾部的分割缺陷，并伴有周期性表达域的破坏，这表明振荡器是后部分割所必需的。然而，前躯干分割的控制及其与后躯干分割的关系尚未得到很好的理解。周期性Her基因her1和her7的联合缺失会破坏前、后轴旁中胚层的分割，这表明her基因在前部分割中发挥冗余功能。为了测试这种前部冗余是her基因家族所特有的，还是分割振荡器更普遍的特征，我们观察了在单独或与her7或其他Delta/Notch通路基因联合使用吗啉代敲低周期性细胞表面Notch配体deltaC（dlc）后的前部分割情况。我们发现，dlc对于周期性基因her1和her7的波状表达域的连贯性及其表达水平的维持，以及dlc自身的周期性转录都是必需的，这证实了dlc是分割振荡器的一个组成部分。在dlc敲低以及与deltaD或notch1a突变体联合使用时，出现了剂量依赖性的、后向受限的分割缺陷。然而，dlc和her7功能的联合降低会导致前、后轴旁中胚层的分割缺陷，以及周期性表达域无法启动，这与两个her基因缺失的情况相似。因此，前部分割同样需要her和delta家族成员的功能，这表明分割振荡器在整个脊椎动物轴的轴旁中胚层中发挥作用。
