Dissecting signaling dynamics underlying self-organized fate patterning of 2D human gastruloids
| dc.contributor.advisor | Warmflash, Aryeh | |
| dc.creator | Chhabra, Sapna | |
| dc.date.accessioned | 2020-04-20T15:07:36Z | |
| dc.date.available | 2020-04-20T15:07:36Z | |
| dc.date.created | 2020-05 | |
| dc.date.issued | 2020-04-13 | |
| dc.date.submitted | May 2020 | |
| dc.date.updated | 2020-04-20T15:07:36Z | |
| dc.description.abstract | Gastrulation is a crucial stage in embryonic development when the epiblast self- organizes to form three germ layers – the ectoderm, mesoderm and endoderm, which eventually form the entire organism. Decades of genetic and biochemical studies in the mouse embryo have revealed that a signaling cascade involving the BMP, WNT and NODAL pathways is necessary for gastrulation. In the developing mouse embryo, WNT and NODAL ligands are expressed near the site of gastrulation, and knockout of these ligands leads to a failure to gastrulate. These data have led to the prevailing view that a signaling gradient in WNT and NODAL underlies germ layer fate patterning during gastrulation. However, the activities of these pathways in space and time have never been directly observed, as gastrulation occurs after the mouse embryo implants in the mother’s uterus, and thus, precludes, direct observation and analyses. Thus, whether a stable signaling gradient of WNT and NODAL activities underlies formation of the three germ layers remains unknown. In this study, we utilize our previously developed model of human gastrulation (2D human gastruloids) where circular colonies of human embryonic stem cells (hESCs), treated with BMP4 ligands, self-organize to form a radial pattern of the three germ layers surrounded by extra-embryonic cells at the colony edge; to measure signaling activities of WNT and NODAL. Our data shows that BMP signaling initiates a wave of WNT signaling that initiates a wave of NODAL signaling. Both WNT and NODAL signaling activities spread towards the colony center at a constant rate. Using a simple mathematical model, we show that this spreading behavior is inconsistent with a reaction- diffusion–based Turing system, indicating that there is no stable signaling gradient of WNT/NODAL signaling activity. Instead, the final signaling state is homogeneous, and spatial differences arise only from boundary effects. We further show that although both WNT and NODAL signaling synergize to enable mesodermal differentiation, neither of them forms a spatial pattern that maps directly to the mesodermal region, suggesting that mesoderm differentiation is controlled by the dynamics of multiple signals. In contrast to this, extra-embryonic differentiation at the colony edge is controlled by the duration of BMP signaling, which is consistently high in extra-embryonic cells. The identity of these extra-embryonic cells has been controversial, with some studies suggesting a trophoblast cell fate and others suggesting an extra-embryonic mesodermal fate. Using RNA- sequencing, we show that these cells are transcriptionally similar to trophoblast cells in the day 7 human embryo. Taken together, our results show that that the dynamics of signaling events in the BMP, WNT, and NODAL cascade in the absence of a stable signaling gradient, instruct germ layer fate patterning in human gastruloids. | |
| dc.format.mimetype | application/pdf | |
| dc.identifier.citation | Chhabra, Sapna. "Dissecting signaling dynamics underlying self-organized fate patterning of 2D human gastruloids." (2020) Diss., Rice University. <a href="https://hdl.handle.net/1911/108327">https://hdl.handle.net/1911/108327</a>. | |
| dc.identifier.uri | https://hdl.handle.net/1911/108327 | |
| dc.language.iso | eng | |
| dc.rights | Copyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder. | |
| dc.subject | Gastruloids | |
| dc.subject | cell-fate patterning | |
| dc.subject | signaling dynamics | |
| dc.subject | Turing system | |
| dc.title | Dissecting signaling dynamics underlying self-organized fate patterning of 2D human gastruloids | |
| dc.type | Thesis | |
| dc.type.material | Text | |
| thesis.degree.department | Systems, Synthetic and Physical Biology | |
| thesis.degree.discipline | Natural Sciences | |
| thesis.degree.grantor | Rice University | |
| thesis.degree.level | Doctoral | |
| thesis.degree.name | Doctor of Philosophy |
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