Wang Yuan, Zeng Huiqing, Liu Aimin
Department of Biology, Eberly College of Sciences, Center for Cellular Dynamics, Huck Institute of Life Science, The Penn State University, University Park, PA 16802, USA.
Department of Occupational Health, School of Public Health, China Medical University, No.77 Puhe Road, Shenyang North New Area, Shenyang 110122, China.
J Dev Biol. 2019 Feb 19;7(1):5. doi: 10.3390/jdb7010005.
The primary cilia play essential roles in Hh-dependent Gli2 activation and Gli3 proteolytic processing in mammals. However, the roles of the cilia in Gli1 activation remain unresolved due to the loss of transcription in cilia mutant embryos, and the inability to address this question by overexpression in cultured cells. Here, we address the roles of the cilia in Gli1 activation by expressing from the locus in mouse embryos. We find that the maximal activation of Gli1 depends on the cilia, but partial activation of Gli1 by Smo-mediated Hh signaling exists in the absence of the cilia. Combined with reduced Gli3 repressors, this partial activation of Gli1 leads to dorsal expansion of V3 interneuron and motor neuron domains in the absence of the cilia. Moreover, expressing from the locus in the presence of reduced Sufu has no recognizable impact on neural tube patterning, suggesting an imbalance between the dosages of Gli and Sufu does not explain the extra Gli1 activity. Finally, a non-ciliary Gli2 variant present at a higher level than Gli1 when expressed from the locus fails to activate Hh pathway ectopically in the absence of the cilia, suggesting that increased protein level is unlikely the major factor underlying the ectopic activation of Hh signaling by Gli1 in the absence of the cilia.
初级纤毛在哺乳动物中依赖Hh的Gli2激活和Gli3蛋白水解加工过程中发挥着重要作用。然而，纤毛在Gli1激活中的作用仍未得到解决，这是由于纤毛突变胚胎中转录缺失，以及无法通过在培养细胞中过表达来解决这个问题。在这里，我们通过在小鼠胚胎中从 位点表达来研究纤毛在Gli1激活中的作用。我们发现Gli1的最大激活依赖于纤毛，但在没有纤毛的情况下，Smo介导的Hh信号通路会导致Gli1部分激活。结合减少的Gli3阻遏物，Gli1的这种部分激活在没有纤毛的情况下导致V3中间神经元和运动神经元区域的背侧扩展。此外，在Sufu减少的情况下从 位点表达对神经管模式没有可识别的影响，这表明Gli和Sufu剂量之间的不平衡并不能解释额外的Gli1活性。最后，当从 位点表达时，一种比Gli1水平更高的非纤毛Gli2变体在没有纤毛的情况下无法异位激活Hh信号通路，这表明蛋白质水平的增加不太可能是Gli1在没有纤毛的情况下异位激活Hh信号的主要因素。
