Dynamics of axial polarization in embryonic stem cell aggregates and the evolution of body axis establishment
- Autores: Lukas-Kerim Anlas
- Directores de la Tesis: Vikas Trivedi (dir. tes.)
- Lectura: En la Universitat Pompeu Fabra ( España ) en 2022
- Idioma: español
- Tribunal Calificador de la Tesis: Miki Matsuda (presid.), Iñaki Ruiz Trillo (secret.), Núria Montserrat Pulido (voc.)
- Programa de doctorado: Programa de Doctorado en Biomedicina por la Universidad Pompeu Fabra
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
- català
En metazous, l’agregació de poques cèl·lules mare embrionàries (CME) in vitro recapitula l'establiment d'un pla corporal bàsic, en particular l'eix anteroposterior (AP). A diferència dels embrions reals els quals requereixen de senyals externes, els agregats de CME són capaços d’adquirir patrons d’expressió gènica fins i tot en l’absència de morfògens externs. Proposem que aquest fenomen és fruit d’una capacitat inherent de les CME la qual reflecteix un mode de desenvolupament conservat. Per a estudiar la generació de l’eix AP in vitro, hem escollit gastruloids derivats de CME de ratolí. Mostrem que trajectòries de diferenciació cel·lular alternatives in vivo i in vitro convergeixen a destins cel·lulars similars. Addicionalment, explorem la variabilitat i robustesa dels modes de desenvolupament dels gastruloids modificant el grau de pluripotencia de la població inicial de CME, estudiant comparativament la dinàmica de polarització. Finalment, els nostres resultats poden servir per a entendre modes inherents de generació de patrons.
- English
This doctoral thesis aims to provide novel insights into the evolution of metazoan (animal) body plan establishment, the role of external or extraembryonic cues in this process and the dynamics of anteroposterior axis as well as germ layer specification in a minimal embryo-like in vitro system, termed “gastruloids”. In what follows, we briefly summarize the theoretical background and the research conducted as part of this work:
Across metazoans, minimal in vitro systems from embryonic stem cells (ESCs) recapitulate the establishment of a basic body plan, in particular the anteroposterior (AP) or oral-aboral (OA) axis. Notably, in contrast to actual embryos which generally require extraembryonic or maternally deposited signals, ESC aggregates undergo initial patterning in the absence of localized, external cues.
Here, we propose that such observations may reflect an inherent capacity of ESCs or similar populations that we summarize as an evolutionarily conserved developmental mode. To dissect the framework of AP axis establishment and concomitant germ layer patterning in a minimal system, we leverage gastruloids, an established embryo-like structure from mouse ESCs.
We show that AP specification, demarcated by polarization of the conserved marker gene T, is robust to a variety of perturbations in the initial conditions, yet remains dependent on the precise temporal activation of key signalling pathways. In addition, we discover that, compared to the native embryo, gastruloids generate similar meso- and endodermal cell types despite initial differences in their primed pluripotent populations which adopt a more mesenchymal state in lieu of an epiblast-like transcriptome. Hence, this argues that alternate differentiation trajectories between in vivo and in vitro may converge onto similar cell fates.
Finally, we delineate variability and robustness of this developmental mode of gastruloids by modifying the (pluripotent) state of the initial ESC population and comparatively assessing T polarization as well as germ layer formation events. We observe that AP symmetry breaking may occur via distinct spatiotemporal gene expression dynamics, with proportions of generated tissue fates exhibiting variation. Furthermore, we elucidate morphogenetic properties of emerging T+ versus T− populations. Altogether, our findings may serve to inform inherent modes of patterning that underlie embryonic development and the generation of biological form in general.
The main structure of this thesis thus comprises an abstract in English and Catalan, an introductory chapter, a results chapter which is separated into two sub-chapters, representing the two main research lines, a discussion chapter, a materials and methods chapter as well as a references or bibliography chapter.
- català
