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MRC DTP: Analysis of the impact on cell responses to varying levels of Notch Signalling in the context of stem cells and the presomitic mesoderm


School of Life Sciences

Prof J K Dale , Friday, January 15, 2021 Competition Funded PhD Project (Students Worldwide)

About the Project

The Notch pathway is crucial to vertebrate development. Aberrant levels of Notch signalling underlies many diseases and cancers.   Somitogenesis is a key  conserved developmental process in which Notch plays an essential role.   When Notch is inhibited, somites are not formed. Moreover, extending NICD half-life decreases the rate of somite formation.

Unlike most major signalling pathways, Notch does not rely on intermediate mediators. Following ligand activation, the intracellular part of the Notch receptor (NICD) is cleaved, translocates into the nucleus and interacts with transcription complexes turning on gene expression. NICD is then rapidly degraded.  Both in development and disease contexts this pathway has been shown to be exquisitely sensitive to NICD levels.

We hypothesise that transcriptional output of specific cohorts of Notch target genes is regulated by different NICD levels thus directing the wide range of subsequent cell behaviours/fate decisions that receiving cells adopt in response to Notch activation.



To test this hypothesis, we will move from the traditional mouse embryo model to engineer human induced pluripotent stem cells (hiPSCs) that drive low or high Notch expression and monitor their differentiation potential, focussing on two derivatives the presomitic mesoderm (PSM), which gives rise to the somites, and caudal neural tube which both derive from an intermediate neuromesodermal progenitor (NMP) cell type.



We will generate a hIPS cell line with differential levels of NICD to discern the effects of differential levels of NICD on stem cell differentiation. This cell line will be generated using CrisprCas9 technology using dCas9-SAM and dCas9-KRAB system to increase or decrease endogenous levels of the Notch receptor respectively. Using established protocols for differentiation of hiPS cells we will determine the differentiation dynamics in our assays. To characterise the effects of varying NICD levels we will use a PSM reporter cell line, western blots and qPCR by looking at several key genes that turn on/off during the time course of differentiation. We will also assess the impact of varying NICD levels on global transcription, both intensity of gene expression and differential target gene expression. Lastly, we will use a recently developed CrisprCas9 targeted cell line, with a non-phosphorylatable serine to alanine point mutation, that extends NICD half-life.  Modulating NICD stability in this way we can in parallel compare i) the time over which the stem cells adopt different cell fates, ii) the choice of cell fate  and/or iii) the target genes the stem cells turn on following changes in NICD levels brought about by either NICD production or NICD degradation.  Our findings will lead to a better understanding of the molecular basis of Notch signalling and its impact on the physiology of stem cells.


References

Recent work from the lab can be found in the following references:

Carrieri, F.A., Murray, P.J., Ditsova, D., Ferris, M.A., Davies, P., Dale, J.K (2019) CDK1 and CDK2 regulate NICD1 turnover and periodicity of the segmentation clock. EMBO Reports. 20, 4, p. 1-22 22 p., e46436 doi/10.15252/embr.201846436 PMID 31267714  Read Article

Murray, P., Carrieri, F.A., Dale, J.K. (2019) Cell cycle regulation of oscillations yields coupling of growth and from in a computational model of the presomitic mesoderm.  Journal of Theoretical Biology. doi/10.1016/j.jtbi.2019.05.006 PMID 31121170 Read Article

Wiedermann, G., Bone, R. A., Dale, J. K., et al. (2015) A balance of positive and negative regulators determines the pace of the segmentation clock. Elife 4: e05842. doi/10.7554/eLife.05842 PMCID 4601006 PMID 26357015 Read Article

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