Biology subjects

Barbaric, I.

Publications and source records attributed to Barbaric, I..

5 recordsLinked to original sources

bioRxiv2019

Genetically variant human pluripotent stem cells selectively eliminate wild-type counterparts through YAP-mediated cell competition

The appearance of genetic changes in human pluripotent stem cells (hPSCs) presents a concern for their use in research and regenerative medicine. Variant hPSCs harbouring recurrent culture-acquired aneuploidies display growth advantages over wild-type diploid cells, but the mechanisms yielding a drift from predominantly wild-type to variant cell populations remain poorly understood. Here we show that the dominance of variant clones in mosaic cultures is enhanced through competitive interactions resulting in elimination of wild-type cells. This elimination occurs through corralling and mechanical compression by faster growing variants, causing a redistribution of F-actin and sequestration of YAP in the cytoplasm that induces apoptosis in wild-type cells. Importantly, YAP overexpression in wild-type cells is sufficient to alleviate their loser phenotype. Our results demonstrate that hPSC fate is coupled to mechanical cues imposed by neighbouring cells and reveal that hijacking this mechanism allows variants to achieve clonal dominance in cultures.

cell biology↗

bioRxiv2019

Nucleosides rescue replication-mediated genome instability of human pluripotent stem cells

Human pluripotent stem cells (PSC) often acquire genetic changes on prolonged culture, which pose concerns for their use in research and regenerative medicine (Amps et al., 2011, Seth et al., 2011). The acquisition of these changes during culture necessarily first requires mutation and then selection of those mutations that provide a growth advantage. Whilst selection accounts for the recurrent nature of the variants commonly reported (Draper et al., 2004, Olariu et al., 2010), the mechanisms of mutation in PSC remain largely elusive. Here we show that, in contrast to somatic cells, human PSC have an increased susceptibility to DNA damage and mitotic errors, both of which are caused by heightened replication stress in PSC and this can be alleviated by culture with exogenous nucleosides. These results reflect the requirement for rapid replication of human PSC enabled by a truncated G1 (Becker et al., 2006, Becker et al., 2010) that impairs the preparation of these cells for the ensuing DNA replication. A similar relationship has been shown in relation to chromosomal instability in cancer cells (Burrell et al., 2013, Wilhelm et al., 2019) but PSC differ by replication stress triggering apoptosis (Desmarais et al., 2012, Desmarais et al., 2016). Nevertheless, evasion of this response still leads to the appearance of genetic variants that are of concern for regenerative medicine. The inclusion of nucleosides into culture media greatly improves the efficiency of human PSC culture and minimises the acquisition of genomic damage.

cell biology↗

bioRxiv2019

DRP1-mediated regulation of mitochondrial dynamics determines the apoptotic response upon embryonic differentiation.

The changes that drive differentiation create a large potential for the emergence of abnormal cells that need to be removed before they contribute to further development or the germline. This removal is in part achieved by cells becoming hypersensitive to death upon exit of naive pluripotency. What causes this change in apoptotic response is unknown. Here we identify that it is controlled by the regulator of mitochondrial dynamics DRP1. We show that in mouse, naive pluripotent cells have fragmented mitochondria due to high DRP1-mediated fission, but upon differentiation, DRP1 activity decreases, inducing mitochondria to fuse and form complex networks. We demonstrate that this decrease in DRP1 activity lowers the apoptotic threshold, as mutation of DRP1 increases the sensitivity to cell death and its over-expression protects against apoptosis. Together, our findings highlight how regulation of mitochondrial dynamics allows cells to adapt their apoptotic response to the changing environment of differentiation.

developmental biology↗

bioRxiv2019

Retinoic acid accelerates the specification of enteric neural progenitors from in vitro-derived neural crest

The enteric nervous system (ENS) is derived primarily from the vagal neural crest, a migratory multipotent cell population emerging from the dorsal neural tube between somites 1-7. Defects in the development and function of the ENS give rise to a range of disorders, termed enteric neuropathies and include conditions such as Hirschsprungs disease. Little is known about the signalling that specifies early ENS progenitors. This has, thus far, limited progress in the generation of enteric neurons from human Pluripotent Stem Cells (hPSCs) that could provide a useful tool for disease modelling and regenerative medicine. We describe the efficient and accelerated generation of ENS progenitors from hPSCs, revealing that retinoic acid is critical for the acquisition of both vagal axial identity and early ENS progenitor specification. These ENS progenitors generate enteric neurons in vitro and following in vivo transplantation, achieving long-term colonisation of the ENS in adult mice. Thus, hPSC-derived ENS progenitors may provide the basis for cell therapy for defects in the ENS.

developmental biology↗

bioRxiv2019

Generation and Trapping of a Mesoderm Biased State of Human Pluripotency

We postulate that exit from pluripotency involves intermediates that retain pluripotency while simultaneously exhibiting lineage-bias. Using a MIXL1 reporter, we explored mesoderm lineage-bias within the human pluripotent stem cell compartment. We identified a substate, which at the single cell level coexpresses pluripotent and mesodermal gene expression programs. Functionally these cells could initiate stem cell cultures and exhibited mesodermal bias in differentiation assays. By promoting mesodermal identity through manipulation of WNT signalling while preventing exit from pluripotency using lysophosphatidic acid, we could trap and maintain cells in a lineage-biased stem cell state through multiple passages. These cells correspond to a normal state on the differentiation trajectory, the plasticity of which is evidenced by their reacquisition of an unbiased state upon removal of differentiation cues. The use of cross-antagonistic signalling to trap pluripotent stem cell intermediates with different lineage-bias may have general applicability in the efficient production of cells for regenerative medicine.

cell biology↗