Biology subjects

Sermon, K.

Publications and source records attributed to Sermon, K..

5 recordsLinked to original sources

bioRxiv2023

Gain of 1q confers an MDM4-driven growth advantage to undifferentiated and differentiating hESC while altering their differentiation capacity

Gains of 1q are a highly recurrent chromosomal abnormality in human pluripotent stem cells. In this work, we show that gains of 1q impact the differentiation capacity to derivates of the three germ layers, leading to miss-specification to cranial placode and non-neural ectoderm during neuroectoderm differentiation and by poorer expression of lineage specific markers in hepatoblasts and cardiac progenitors. Competition assays show that the cells retain their selective advantage during differentiation, which is mediated by a higher expression of MDM4, a gene located in the common region of gain. MDM4 drives the winner phenotype of the mutant cells in both the undifferentiated and differentiating state by reducing the cells sensitivity to DNA-damage through decreased p53-mediated apoptosis. Finally, we find that cell density in culture plays a key role in promoting the competitive advantage of the cells by increasing DNA damage.

cell biology↗

bioRxiv2022

Lineage segregation in human pre-implantation embryos is specified by YAP1 and TEAD1

We know that polarity and YAP1 play a key role in trophectoderm initiation in compacted human embryos, however we know little about the TEAD family of transcription factors that become activated by YAP1 and especially if they play a role during epiblast and primitive endoderm formation. Here we show that compaction occurs heterogeneously between the 8- and 16-cell stages. While 8-cell stage blastomeres are not yet polarized, polarized outer cells and non-polarized inner cells arise in compacted 16-cell stage embryos. While trophectoderm specifiers TEAD1, YAP1 and GATA3 mostly co-localise in the nuclei of polarized outer/trophectoderm cells, they are also found in some cells of compacting embryos before polarity is established indicating that differentiation into trophectoderm cells can be initiated independently of polarity. In the inner cell mass, TEAD1 and YAP1 also distinguish GATA4 positive cells in a salt-and-pepper distribution and in the sorted primitive endoderm cells. Our detailed roadmap on polarization, compaction, position and lineage segregation events during human preimplantation development paves the road for further functional studies. Fundamental knowledge of lineage segregation events will eventually explain how and why embryos fail to develop further before or during implantation.

developmental biology↗

bioRxiv2022

Aneuploidy triggers autophagy and p53-mediated apoptosis and impairs second lineage segregation in human preimplantation embryos

About 70% of human cleavage stage embryos show chromosomal mosaicism, falling to 20% in blastocysts. Chromosomally mosaic human blastocysts can implant and lead to healthy new-borns with normal karyotypes. Studies in mouse embryos and human gastruloids have shown that aneuploid cells show proteotoxic stress, autophagy and p53 activation and that they are eliminated from the epiblast by apoptosis while being tolerated in the trophectoderm. These observations suggest a selective loss of aneuploid cells from human embryos, but the underlying mechanisms are not yet fully understood. In this study we investigated the cellular consequences of aneuploidy in a total of 125 human blastocysts. RNA-sequencing of trophectoderm cells showed transcriptional signatures of activated p53 pathway and apoptosis, which was proportionate to the level of chromosomal imbalance. Immunostaining corroborated that aneuploidy triggers proteotoxic stress, autophagy, p53-signalling, and apoptosis independent from DNA damage. Total cell numbers were lower in aneuploid embryos, due to a decline both in trophectoderm and in epiblast/primitive endoderm cell numbers. While lower cell numbers in trophectoderm may be attributed to apoptosis, it appeared that aneuploidy impaired the second lineage segregation, particularly primitive endoderm formation. This might be reinforced by retention of NANOG in aneuploid embryos. Our findings might explain why fully aneuploid embryos fail to further develop and we hypothesize that the same mechanisms lead to removal of aneuploid cells from mosaic embryos. This hypothesis needs further study as we did not analyze chromosomal mosaic embryos. Finally, we demonstrated a few differences with previous findings in the mouse, emphasizing the need for human embryo research to understand the consequences of aneuploidy.

developmental biology↗

bioRxiv2020

Endogenous suppression of WNT signalling in human embryonic stem cells leads to low differentiation propensity towards definitive endoderm

SummaryLow differentiation propensity towards a targeted lineage can significantly hamper the utility of individual human pluripotent stem cell (hPSC) lines in biomedical applications. Here, we use monolayer and micropatterned cell cultures, as well as transcriptomic profiling, to investigate how variability in signalling pathway activity between human embryonic stem cell lines affects their differentiation efficiency towards definitive endoderm (DE). We show that endogenous suppression of WNT signalling in hPSCs at the onset of differentiation prevents the switch from self-renewal to DE specification. Gene expression profiling reveals that this inefficient switch is reflected in NANOG expression dynamics. Importantly, we demonstrate that higher WNT stimulation or inhibition of the PI3K/AKT signalling can overcome the DE commitment blockage. Our findings highlight that redirection of the activity of Activin/NODAL pathway by WNT signalling towards mediating DE fate specification is a vulnerable spot, as disruption of this process can result in poor hPSC specification towards DE.Competing Interest StatementThe authors have declared no competing interest.View Full Text

cell biology↗

bioRxiv2020

Constitutional activation of BMP4 and WNT signalling in hESC results in impaired mesendoderm differentiation

We identified a human embryonic stem cell subline that fails to respond to the differentiation cues needed to obtain mesendoderm derivatives, differentiating into trophoblast-like cells instead. RNA-sequencing analysis showed that the subline has hyperactivation of the WNT and BMP4 signalling. Modulation of these pathways with small molecules confirmed them as the cause of the differentiation impairment. While activation of WNT and BMP4 in control cells resulted in a loss of mesendoderm differentiation and induction of trophoblast markers, inhibition of these pathways in the subline restored its ability to differentiate. Karyotyping and exome sequencing analysis did not identify any changes in the genome that could account for the pathway deregulation. These findings add to the increasing evidence that different responses of stem cell lines to differentiation protocols are based on genetic and epigenetic factors, inherent to the line or acquired during cell culture.

cell biology↗