Tree Genetics and Molecular Breeding 2024, Vol.14, No.4, 166-176 http://genbreedpublisher.com/index.php/tgmb 169 in trees is similar to those found in other organisms, comprising various cellular and extracellular components that provide biochemical and mechanical signals to the stem cells (Singh, 2012; Ema and Suda, 2012; Chacón-Martínez et al., 2018). These niches are located in specific regions such as the shoot, root, and vascular meristems, which are responsible for the formation of new organs and tissues throughout the tree's life (Aichinger et al., 2012). Figure 2 Dynamics of Notch signalling (Adopted from Sonnen and Janda, 2021) Image caption: (A) Notch is generated in the endoplasmic reticulum and travels to the plasma membrane via the Golgi apparatus. In the Golgi, the first proteolytic cleavage is mediated by Furin, which leads to the formation of a Notch heterodimer. There, Notch binding affinities can be modulated by post-translational modifications, e.g. glycosylation by Fringe. When the ligand from a neighbouring cell interacts with Notch, a mechanical pulling force results in a conformational change in Notch. This allows the proteolytic cleavage of Notch by ADAM and then γ-Secretase, which finally releases NICD (Notch intracellular domain) into the cytoplasm. In the nucleus, NICD interacts with the transcription factor CSL and the co-activator Mam to induce the expression of Notch target genes. Among these are Hes genes, which initiate a delayed negative feedback loop, as well as Fringe and Nrarp, which both feed back onto Notch signalling. Finally, NICD is phosphorylated and degraded by the proteasome. (B) Due to the negative feedback loop of Hes proteins, Hes expression oscillates in many systems. In neural stem cells of the developing brain Hes1 oscillates alternatingly with pro-neural genes. When Hes1 oscillations cease and pro-neural proteins get stabilized, cells differentiate. (C) Neighbouring cells can couple via Notch signalling and synchronize their intracellular oscillations, for instance during periodic segmentation of vertebrate embryos. This is thought to be achieved by reciprocal activation of Notch signalling in neighbouring cells and induction of the ligand Dll1 (Adopted from Sonnen and Janda, 2021)
RkJQdWJsaXNoZXIy MjQ4ODYzMg==