Investigating the role of Notch signalling during mesoderm development and cell proliferation

Communication among cells drives organismal development and homeostasis in all multicellular organisms. Understanding how cells communicate with one another is critical to understanding mechanisms underlying developmental and diseases processes. The Notch signalling pathway is a cell-contact-dependent pathway known to regulate cell proliferation, differentiation, and specification in a context-dependent manner. Owing to its crucial function during all stages of life, it is highly conserved between vertebrates and invertebrates. Notch signalling activation leads to the cleavage of the receptor protein and its transit to the nucleus, where it also acts as its own effector and regulates target gene expression. This unique characteristic renders cells and tissues sensitive to varying levels of Notch activation. Although widely studied, the role of Notch signalling during mesodermal specification remains unclear. In addition, novel insight, which revealed that human Notch1 forms nuclear biomolecular condensates, raised questions regarding the effect of physical interactions between Notch1 proteins and target gene RNA products on transcriptional regulation and dynamics. Here, we aimed to answer the two questions outlined above using two different model systems. Using Drosophila melanogaster embryos, we aimed to investigate the role of Notch signalling during mesodermal specification, because of the high degree of conservation of this pathway between humans and Drosophila melanogaster and the ease of dissecting genetic interactions in vivo in this model system. Our findings showed that Notch signalling directly regulates the expression of several mesodermal genes during early embryogenesis. We also found that Notch signalling indirectly regulates the activity of Dorsal, a transcription factor known to govern mesoderm specification and early embryonic patterning. Secondly, we used human cell lines to generate novel molecular tools that allowed the visualisation of Notch1 target gene, c-MYC, RNA and proteins endogenously in real-time. Using these tools, we found that Notch1 interacts with both c-MYC RNA and proteins. We found that the increases in c-MYC RNA levels do not destabilize Notch1 condensates. Intriguingly, we found evidence that points to a potential role of Notch1 during post-transcriptional regulation of gene expression, where Notch1 sequesters RNA molecules and potentially recruits RNA-binding proteins to either facilitate or inhibit their translation.

Name thesis:degree_name

Ph.D. Biological Sciences

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Faculty of Mathematics and Science

Department dc:contributor.department

Department of Biological Sciences

Grantor dc:publisher

Brock University

Year dc:date.issued

2025

Author dc:creator

• Megaly, Marvel

Advisor dc:contributor.advisor

• Necakov, Aleksandar

• Notch
• Drosophila
• Development
• Cancer

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/10464/19658

OAI identifier oai:identifier

oai:brocku.scholaris.ca:10464/19658