2023 Project 3

Student Projects 2023: 1 Patterning neural border and NC | 2 NPB NEUcrest | 3 EMT and NC | 4 miRNA and NC | 5 Adrenal Gland and NC | 6 Melanocyte & Melanoma | 7 Neurocristopathies | Neural Crest These projects are the sole work of undergraduate science students and may contain errors in fact or descriptions.

The Epithelial to Mesenchymal Transition and Neural Crest

Epithelial to mesenchymal transition (EMT) is a crucial step during embryonic development, during which cells undergo transcriptional and morphological changes to delaminate from their place of origin. A paradigmatic example is the neural crest, in which cells delaminate from the neural tube and migrate to their destination. During EMT, cells lose their epithelial characteristics (e.g. cell-cell adhesion and apico-basal polarity) and gain mesenchymal phenotypes (e.g. cell elongation, front-rear polarity, protrusions). EMT is induced by the expression of EMT transcription factors (EMT-TFs), including members of the Snail, Twist, Zeb and Prrx families among others. EMT-TFs repress the expression of cell-cell adhesion proteins and activate mesenchymal programmes. All of these changes include cytoskeletal reorganization, changes in cell shape and frequently, regulation of cell division and increased survival. In the epithelial state, type I cadherins (mainly E-cadherin), tight junction, and adhesion junctions mediate strong cell-cell interaction. During EMT, cells gradually lose the cell-cell contacts by transcriptionally repressing adherens and tight junction proteins and switching to type II cadherins (Cadherin 7 and cadherin 11) or N-cadherin in the mesoderm or in cancer. Epithelial cells are stabilized by their extracellular matrix, which has to be remodelled and degraded during EMT7. Furthermore, rearrangement of the actin cytoskeleton leads to cell elongation, front-rear cell polarity, and directional motility.

EMT is generally known as an embryonic process, however in the last decades many studies have reported its re-activation during adult pathological conditions, such as fibrosis and cancer9,10. The EMT process exclusively refers to epithelial cells, however there are other types of cells that, undergoing a similar mechanism to acquire mesenchymal features. An important example comes from the melanoma biology, where deregulated melanocytes can undergo a comparable process, generally called epithelial-to-mesenchymal-like transition (EMT-like process), also known as phenotypic switching11. Melanocytes are pigment-producing cells, whose progenitors are neural crest cells. Thus, it is not surprising that the melanoma phenotypic switching is mediated by molecular events that resemble the ones in the EMT. Many similarities characterise phenotypic switching and embryonic EMT. Among them there are cell-biological changes, such as increased migration and invasion capacity, and gene expression changes, including a switch in expression of of EMT-TFs pairs11. Moreover, as happens for embryonic EMT, melanoma cells, undergoing the phenotypic switching, present different transitional states, not supporting the existence of two dichotomic states, but including hybrid phenotypes with expression of both epithelial and mesenchymal markers3,11.

Phenotypic switching activation is fundamental for melanoma progression. Indeed, it induces cancer cell delamination with subsequent migration and dissemination all over the body. Moreover, it has been also associated with the emergence of therapy resistance1,11. Targeting therapies against EMT have to be taken with caution, as EMT inhibition could lead to the promotion of mesenchymal to epithelial (MET)-like process, fundamental for metastatic colonisation12. However, identifying specific vulnerabilities of cells that transition through EMT will undoubtedly provide improved therapeutic strategies.

In-silico investigation of biological processes gives us split advantages in terms of time, effort and cost, to propose new hypotheses or support existing ones. The recent advancement in next generation sequencing technologies13 opens new opportunities to decipher molecular changes at the single-cell resolution. During EMT, a cell undergoes a series of modifications, therefore, to trace and study this program at single cell level is crucial. scRNA-Seq (single cell RNA Sequencing) coupled with other Omics technologies help in the identification of cell-states and can also infer trajectories, pseudo-time, regulatory modules etc.13. All of this allows building putative gene regulatory networks and predict potential new targets in gene regulatory networks.

Importantly, all these predictions need to be validated with further experimental work, but open a new universe of understanding developmental biology and adult homeostasis while informing on potential avenues to design better therapeutic strategies for congenital malformation, cancer and fibrosis.

References

1. Dongre, A. & Weinberg, R. A. New insights into the mechanisms of epithelial–mesenchymal transition and implications for cancer. Nat. Rev. Mol. Cell Biol. 20, 69–84 (2019). PMID: 30459476 Review.

2. Lamouille, S., Xu, J. & Derynck, R. Molecular mechanisms of epithelial–mesenchymal transition. Nat. Rev. Mol. Cell Biol. 15, 178–196 (2014). PMID: 24556840 Review.

3. Nieto, M. A., Huang, R. Y. Y. J., Jackson, R. A. A. & Thiery, J. P. P. Emt: 2016. Cell 166, 21–45 (2016). PMID: 27368099 Review.

4. Theveneau, E. & Mayor, R. Neural crest delamination and migration: From epithelium-to-mesenchyme transition to collective cell migration. Dev. Biol. 366, 34–54 (2012). PMID: 22261150 Review.

5. Gallik, K. L. et al. Neural crest and cancer: Divergent travelers on similar paths. Mech. Dev. 148, 89–99 (2017). PMID: 28888421

6. Simões-Costa, M. & Bronner, M. E. Establishing neural crest identity: a gene regulatory recipe. Dev. Camb. Engl. 142, 242–257 (2015). PMID: 25564621

7. Zhao, R. & Trainor, P. A. Epithelial to mesenchymal transition during mammalian neural crest cell delamination. Semin. Cell Dev. Biol. S1084952122000568 (2022) doi:10.1016/j.semcdb.2022.02.018. PMID: 35277330 Review.

8. Huang, R. Y.-J., Guilford, P. & Thiery, J. P. Early events in cell adhesion and polarity during epithelial-mesenchymal transition. J. Cell Sci. 125, 4417–4422 (2012).. PMID: 23165231 Review.

9. Thiery, J. P., Acloque, H., Huang, R. Y. J. & Nieto, M. A. Epithelial-Mesenchymal Transitions in Development and Disease. Cell 139, 871–890 (2009).

10. Brabletz, T., Kalluri, R., Nieto, M. A. & Weinberg, R. A. EMT in cancer. Nat. Rev. Cancer 18, 128–134 (2018).

11. Pedri, D., Karras, P., Landeloos, E., Marine, J. & Rambow, F. Epithelial‐to‐mesenchymal‐like transition events in melanoma. FEBS J. 289, 1352–1368 (2022).

12. Nieto, M. A. Epithelial plasticity: A common theme in embryonic and cancer cells. Science 342, (2013).

13. Macosko, E. Z. et al. Highly Parallel Genome-wide Expression Profiling of Individual Cells Using Nanoliter Droplets. Cell 161, 1202–1214 (2015).