Biology subjects

Harmston, N.

Publications and source records attributed to Harmston, N..

10 recordsLinked to original sources

bioRxiv2026

Single cell RNA sequencing of D. pseudoobscura testes reveals transcriptional signatures of heteromorphic spermatogenesis

Sperm heteromorphy, the production of multiple sperm morphs with distinct functions, has evolved repeatedly in animals but its developmental and molecular basis remains poorly understood. In the Drosophila obscura group, males produce fertilising eusperm and non-fertilising parasperm, yet when and how these lineages diverge is unclear. Here, we applied single-cell RNA sequencing to whole testes of D. pseudoobscura to resolve cell-type composition, developmental trajectories, and transcriptional differences between sperm morphs. Analysis of [~]6,500 cells across two replicates identified germline and somatic cell populations and reconstructed spermatogenesis from stem cells to elongated spermatids. We identified a bifurcation in the germline trajectory at the early spermatocyte stage, corresponding to eusperm and parasperm lineages, which was maintained through spermiogenesis. Euspermatocytes, destined to generate longer eusperm, exhibited higher transcriptional activity than paraspermatocytes. Differentially expressed genes included structural sperm tail components, chromatin condensation proteins, post-meiotically transcribed genes and gene duplications resulting in paralogues with reciprocal expression patterns. We also identified markers of somatic cyst cells, including head and tail cyst cells, but found no evidence of morph-specific specialisation within the cyst cell lineage. The transcriptional activities of the distinct germline trajectories corresponded with differential expression of orthologues of critical transcriptional regulators known in D. melanogaster. The transcriptional activator TGIF was enriched in euspermatocytes, while the transcriptional repressor kmg was upregulated in paraspermatocytes. GFP-tagged Kmg showed higher abundance and greater chromatin localisation in paraspermatocytes. These findings demonstrate that sperm morph identity is first apparent in early primary spermatocytes and is largely germline intrinsic. We propose that differential transcriptional provisioning and developmental timing underpin sperm length, providing a framework for understanding the evolution and regulation of sperm heteromorphy.

developmental biology↗

bioRxiv2025

Identification of Wnt regulated genes that are repressed by, or independent of, β-catenin

Wnt signaling regulates metazoan development and homeostasis, in part by {beta}-catenin dependent activation and repression of a large number of genes. However, Wnt signaling also regulates genes independent of {beta}-catenin, genes that are less well characterized. In this study, using a pan-Wnt inhibitor we performed a comprehensive transcriptome analysis in a Wnt-addicted orthotopic cancer model to delineate the {beta}-catenin-dependent and independent arms of Wnt signaling. We find that while a large percentage of Wnt-regulated genes are regulated by {beta}-catenin, ten percent of these genes are regulated independent of {beta}-catenin. Interestingly, a large proportion of these {beta}-catenin independent genes are Wnt-repressed. Among the {beta}-catenin dependent genes, more than half are repressed by {beta}-catenin. We used this dataset to investigate the mechanisms by which Wnt/{beta}-catenin signaling represses gene expression, revealing the role of a cis-regulatory motif, the negative regulatory element (NRE). The NRE motif is enriched in the promoters of {beta}-catenin repressed genes and is required for their repression. This provides a comprehensive analysis of the {beta}-catenin independent arm of the Wnt signaling pathway in a cancer model and illustrates how a cis-regulatory grammar can determine Wnt-dependent gene activation versus repression.

cell biology↗

bioRxiv2024

FOXO-regulated Deaf1 controls muscle regeneration through autophagy

The commonality between various muscle diseases is the loss of muscle mass, function, and regeneration, which severely restricts mobility and impairs the quality of life. With muscle stem cells (MuSCs) playing a key role in facilitating muscle repair, targeting regulators of muscle regeneration has been shown to be a promising therapeutic approach to repair muscles. However, the underlying molecular mechanisms driving muscle regeneration are complex and poorly understood. Here, we identified a new regulator of muscle regeneration, Deformed epidermal autoregulatory factor 1 (Deaf1) - a transcriptional factor downstream of FOXO signaling. We showed that Deaf1 is transcriptionally repressed by FOXOs and that Deaf1 targets to PI3KC3 and Atg16l1 promoter regions and suppresses their expressions. Deaf1 depletion therefore induces autophagy, which in turn blocks MuSC survival and differentiation. In contrast, Deaf1 overexpression inactivates autophagy in MuSCs, leading to increased protein aggregation and cell death. Interestingly, Deaf1 depletion and overexpression both lead to defects in muscle regeneration, highlighting the importance of fine tuning Deaf1-regulated autophagy during muscle regeneration. We further showed that Deaf1 expression is altered in aging and cachectic MuSCs. Remarkably, manipulation of Deaf1 expression can attenuate muscle atrophy and restore muscle regeneration in aged mice or mice with cachectic cancers. Together, our findings unveil an evolutionarily conserved role for Deaf1 in muscle regeneration, providing insights into the development of new therapeutic strategies against muscle atrophy.

cell biology↗

bioRxiv2024

Aberrant non-canonical NF-kappaB signalling reprograms the epigenome landscape to drive oncogenic transcriptomes in multiple myeloma

In multiple myeloma, abnormal plasma cells establish oncogenic niches within the bone marrow by engaging the NF-{kappa}B pathway to nurture their survival while they accumulate pro- proliferative mutations. Under these conditions, many cases eventually develop genetic abnormalities endowing them with constitutive NF-{kappa}B activation. Here, we find that sustained NF-{kappa}B/p52 levels resulting from such mutations favours the recruitment of enhancers beyond the normal B-cell repertoire. Furthermore, through targeted disruption of p52, we characterise how such enhancers are complicit in the formation of super-enhancers and the establishment of cis-regulatory interactions with myeloma dependencies during constitutive activation of p52. Finally, we functionally validate the pathological impact of these cis- regulatory modules on cell and tumour phenotypes using in vitro and in vivo models, confirming RGS1 as a novel p52-dependent myeloma driver. We conclude that the divergent epigenomic reprogramming enforced by aberrant non-canonical NF-{kappa}B signalling potentiates transcriptional programs beneficial for multiple myeloma progression.

cancer biology↗

bioRxiv2022

Combining Stem Cell Rejuvenation and Senescence Targeting to Synergistically Extend Lifespan

Why biological age is a major risk factor for many of the most important human diseases remains mysterious. We know that as organisms age, stem cell pools are exhausted while senescent cells progressively accumulate. Independently, induction of pluripotency via expression of Yamanaka factors (Oct4, Klf4, Sox2, c-Myc; OKSM) and clearance of senescent cells have each been shown to ameliorate cellular and physiological aspects of aging, suggesting that both processes are drivers of organismal aging. However, stem cell exhaustion and cellular senescence likely interact in the etiology and progression of age-dependent diseases because both undermine tissue and organ homeostasis in different if not complementary ways. Here, we combine transient cellular reprogramming (stem cell rejuvenation) with targeted removal of senescent cells to test the hypothesis that simultaneously targeting both cell-fate based aging mechanisms will maximize life and health span benefits. We show that these interventions protect the intestinal stem cell pool, lower inflammation, activate pro-stem cell signaling pathways, and synergistically improve health and lifespan. Our findings suggest that a combination therapy, simultaneously replacing lost stem cells and removing senescent cells, shows synergistic potential for anti-aging treatments. Our finding that transient expression of both is the most effective suggests that drug-based treatments in non-genetically tractable organisms will likely be the most translatable.

developmental biology↗

bioRxiv2021

Wnt signaling rescues amyloid beta induced stem cell loss

Previously, we established an optogenetic model to induce Amyloid-{beta} intracellular oligomerization to model distinct disease etiologies (LO_SCPLOWIMC_SCPLOW et al. 2020). Here we examine the effect of Wnt signaling on Amyloid in this model. We observe that Wnt activation rescues the detrimental effects of Amyloid expression and oligomerization. We analyze the gene expression changes downstream of Wnt that contribute to this rescue and find changes in aging related genes, protein misfolding, metabolism and inflammation. We propose that Wnt expression reduces inflammation through repression of Toll activating factors and confirm that chronic Toll activation reduces lifespan. We propose that the protective effect observed for Lithium treatment functions at least in part through Wnt activation and inhibition of inflammation.

cell biology↗

bioRxiv2021

A Non-Canonical Raf Function Is Required for Dorsal-Ventral Patterning During Drosophila Embryogenesis

Proper embryonic development requires directional axes to pattern cells into embryonic structures. In Drosophila, spatially discrete expression of transcription factors determines the anterior to posterior organization of the early embryo, while the Toll and TGF{beta} signalling pathways determine the early dorsal to ventral pattern. Embryonic MAPK/ERK signaling contributes to both anterior to posterior patterning in the terminal regions and to dorsal to ventral patterning during oogenesis and embryonic stages. Here we describe a novel loss of function mutation in the Raf kinase gene, which leads to loss of ventral cell fates as seen through the loss of the ventral furrow, the absence of Dorsal/NF{kappa}B nuclear localization, the absence of mesoderm determinants Twist and Snail, and the expansion of TGF{beta}. Gene expression analysis showed cells adopting ectodermal fates much like loss of Toll signaling. Our results combine novel mutants, live imaging, optogenetics and transcriptomics to establish a novel role for Raf, that appears to be independent of the MAPK cascade, in embryonic patterning.

developmental biology↗

bioRxiv2020

Wnt-regulated lncRNA discovery enhanced by in vivo identification and CRISPRi functional validation

BackgroundWnt signaling is an evolutionarily conserved developmental pathway that is frequently hyperactivated in cancer. While multiple protein-coding genes regulated by Wnt signaling are known, the functional lncRNAs regulated by Wnt signaling have not been systematically characterized. ResultsWe comprehensively mapped lncRNAs from an orthotopic Wnt-addicted pancreatic cancer model, identifying 3,633 lncRNAs, of which 1,503 were regulated by Wnt signaling. We found lncRNAs were much more sensitive to changes in Wnt signaling in xenografts than in cultured cells. To functionally validate Wnt-regulated lncRNAs, we performed CRISPRi screens to assess their role in cancer cell proliferation. Consistent with previous genome-wide lncRNA CRISPRi screens, around 1% (13/1,503) of the Wnt-regulated lncRNAs could modify cancer cell growth in vitro. This included CCAT1 and LINC00263, previously reported to regulate cancer growth. Using an in vivo CRISPRi screen, we doubled the discovery rate, identifying twice as many Wnt-regulated lncRNAs (25/1,503) that had a functional effect on cancer cell growth. ConclusionsOur study demonstrates the value of studying lncRNA functions in vivo, provides a valuable resource of lncRNAs regulated by Wnt signaling and establishes a framework for systematic discovery of functional lncRNAs.

genomics↗

bioRxiv2018

In vivo generation of post-infarct mouse cardiac muscle by cardiomyocyte progenitors produced with a reproducible laminin-promoted human stem cell differentiation system

Regeneration of human heart muscle after injury is extremely limited and an unmet clinical need. Despite extensive research, there are no methods for the reproducible generation of clinical quality stem-cell-derived cardiovascular progenitors (CVPs). Here, we identified laminin-221 (LN-221) as the main cardiac laminin, which was produced here as human recombinant protein, and showed that LN-221 promotes differentiation of pluripotent hESCs towards cardiomyocyte lineage and downregulates genes associated with pluripotency and teratoma development. We developed a chemically defined, xeno-free laminin-based cardiomyocyte differentiation protocol to reproducibly generate CVPs that form human muscle in vivo. We assessed the reproducibility of the differentiation protocol using time-course bulk RNA sequencing developed from two different hESC lines. Single-cell RNA sequencing of CVPs derived from two hESC lines further showed high reproducibility and identified three main progenitor subpopulations. These CVPs were transplanted into myocardial infarction mice, where heart function was measured by echocardiogram and human heart muscle bundle formation was identified histologically. This method may provide clinical quality cells for use in regenerative cardiology.

cell biology↗

bioRxiv2017

An Embryonic System To Assess Wnt Transcriptional Targets

During animal development, complex signals determine and organize a vast number of tissues using a very small number of signal transduction pathways. These developmental signaling pathways determine cell fates through a coordinated transcriptional response that remains poorly understood. The Wnt pathway is involved in a variety of these cellular functions, and its signals are transmitted in part through a {beta}-catenin/TCF transcriptional complex. Here we report an in vivo Drosophila assay that can be used to distinguish between activation, de-repression and repression of transcriptional responses, separating upstream and downstream pathway activation and canonical/non-canonical Wnt signals in embryos. We find specific sets of genes downstream of both {beta}-catenin and TCF with an additional group of genes regulated by Wnt, while the non-canonical Wnt4 regulates a separate cohort of genes. We correlate transcriptional changes with phenotypic outcomes of cell differentiation and embryo size, showing our model can be used to characterize developmental signaling compartmentalization in vivo.

developmental biology↗