Biology subjects

Frith, T. J. R.

Publications and source records attributed to Frith, T. J. R..

5 recordsLinked to original sources

bioRxiv2025

Hierarchical lineage architecture of human and avian spinal cord revealed by single-cell genomic barcoding

The formation of neural circuits depends on the precise spatial and temporal organisation of neuronal populations during development. In the vertebrate spinal cord, progenitors are patterned into molecularly defined domains, but how lineage relationships shape neuronal diversity and function has remained unclear. Here, we combine genomic barcoding with single- cell RNA sequencing in chick and human embryos to generate cell-type-resolved clonal maps. We find that spinal neurogenesis follows a hierarchical organisation in which the neural tube first partitions into five broad subdivisions that resolve into the eleven progenitor domains generating the cardinal neuronal classes. This bifurcating architecture implies a patterning mechanism of sequential binary decisions. The most prominent lineage restriction occurs at the embryonic alar-basal boundary, separating sensory-processing from motor-control circuits. Individual progenitors generate neurons across multiple temporal waves while remaining constrained within their lineage subdivision, demonstrating persistence of spatial identity despite temporal competence changes. Among sensory populations, we identify two developmental routes, via unifated or bifated progenitors, to pain- and itch-processing interneurons. These principles are conserved between chick and human, with clonal analysis in human embryos revealing that most fate choices are resolved by six weeks post-conception. Together, these findings provide a framework for spinal cord development and reveal lineage compartmentalisation as a fundamental principle in neural circuit assembly and evolution.

developmental 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

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↗

bioRxiv2018

Human axial progenitors generate trunk neural crest cells

The neural crest (NC) is a multipotent embryonic cell population generating distinct cell types in an axial position-dependent manner. The production of NC cells from human pluripotent stem cells (hPSCs) is a valuable approach to study human NC biology. However, the origin of human trunk NC remains undefined and therefore current in vitro differentiation strategies induce only a modest yield of trunk NC cells. Here we show that hPSC-derived axial progenitors, the posteriorly-located drivers of embryonic axis elongation, give rise to trunk NC cells and their derivatives. Moreover, we define the molecular signatures associated with the emergence of human NC cells of distinct axial identities in vitro. Collectively, our findings indicate that there are two routes toward a human post-cranial NC state: the birth of cardiac and vagal NC is facilitated by retinoic acid-induced posteriorisation of an anterior precursor whereas trunk NC arises within a pool of posterior axial progenitors.

developmental biology↗