Nika Shakiba (PhD defence): Elucidating the reprogramming mechanism: selection pressures direct a poised subpopulation of somatic cells to an induced pluripotent stem cell state

When:
June 20, 2017 @ 1:00 pm – 2:00 pm
2017-06-20T13:00:00-04:00
2017-06-20T14:00:00-04:00
Where:
RS 412
164 College St
Toronto, ON M5S 3E2
Canada

Elucidating the reprogramming mechanism: selection pressures direct a poised subpopulation of somatic cells to an induced pluripotent stem cell state

* This is an open PhD defence—all welcome. *

PhD Candidate

Nika Shakiba

Supervisor

Peter Zandstra, University Professor

Abstract

Through the overexpression of key transcription factors – Oct4, Sox2, Klf4, and c-Myc – somatic cells can be reprogrammed to an induced pluripotent stem cell (iPSC) state, enabling them to give rise to all cell types of the body.

However, the process of reprogramming remains incompletely understood. While comprehensive molecular analyses have mapped global state transitions during population reprogramming, these data do not account for heterogeneity between cells.

In contrast, clonal studies, though useful for documenting cell potential, provide little insight into the impact of cell interactions on reprogramming outcomes.

Here, we aim to consolidate the apparent dichotomy between stepwise cell state changes observed in population reprogramming with the stochasticity of isolated clonal reprogramming.

We first develop a surface marker strategy to track transgene-dependent and -independent iPSCs, enabling us to map heterogeneous reprogramming subpopulations with ease.

We next combine this surface marker-based approach with clonal tracking and mathematical modeling to investigate the reprogramming trajectory of individual reprogramming cells in bulk culture.

In doing so, we uncover clonal competition as a novel driver of population reprogramming dynamics. In fact, we show that a subset of poised somatic cells gives rise to clones that have an elite propensity to dominate bulk reprogramming culture and contribute to the iPSC fraction.

We also show, for the first time, that a few clones overtake population culture, thus making population-averaged data clonally biased.

This work provides novel insights into the role of cell competition in driving heterogeneity in reprogramming culture, providing a new lens with which to interpret population-averaged ‘omics datasets.

Taken together, we show that not all reprogramming clones exhibit equivalent behaviour in multicellular contexts, underscoring the need to consider the competition potential of iPSCs.