Biology subjects

Hubbard, E. J. A.

Publications and source records attributed to Hubbard, E. J. A..

7 recordsLinked to original sources

bioRxiv2025

Non-autonomy of age-related morphological changes in the C. elegans germline stem cell niche

Declines in tissue renewal and repair due to alterations in tissue stem cells is a hallmark of aging. Many stem cell pools are maintained morphologically complex niches. Using the C. elegans hermaphrodite germline stem cell system, we analyzed age-related changes in the morphology of the niche, the distal tip cell (DTC), and identified a molecular mechanism that promotes a subset of these changes. We found decreases in the number and length of long DTC processes with age. We also found that a long-lived daf-2 mutant exhibits a daf-16-dependent maintenance of long DTC processes. Surprisingly, the tissue requirement for daf-16(+) is non-autonomous, and daf-16(+) in body wall muscle is both necessary and sufficient. In addition, after a delay, pre-formed DTC processes deteriorate upon premature germline differentiation, but not upon cell cycle inhibition. We propose a reciprocal DTC-germline interaction model and speculate how reduced daf-2 activity both delays stem cell exhaustion and maintains DTC processes. These studies establish the C. elegans DTC as a powerful in vivo model for understanding age-related changes in cellular morphology and their consequences in stem cell systems. SUMMARYThe C. elegans germline stem cell niche morphology is markedly altered with age and is regulated non-autonomously from the muscle by insulin/IGF-like signaling. Results suggest reciprocal niche-germline regulation.

cell biology↗

bioRxiv2025

Intestinal RICT-1 regulates the larval germline progenitor pool via the vitellogenin VIT-3 in C. elegans

Highly conserved signaling pathways communicate cellular and organismal nutrient conditions to proliferating pools of cells such as stem cells and tumors. One such pathway is the Target of Rapamycin (TOR) pathway. The TOR kinase exists in two complexes, TOR complex 1 (TORC1) and TOR complex 2 (TORC2). In the Caenorhabditis elegans hermaphrodite, TORC1 signaling cell-autonomously promotes the establishment of the larval germline Progenitor Zone (PZ). Here, we show that RICT-1, the sole C. elegans ortholog of the TORC2-specific component Rictor, also promotes expansion of the larval PZ through canonical TORC2 signaling. Unlike the TORC1 components, intestinal rict-1 is both necessary and sufficient for full germline PZ pool establishment. Comparative RNA-seq on staged L4 larvae indicates that intestinal RICT-1 likely acts via vitellogenins. These intestinally produced yolk proteins provision oocytes, but they were not previously known to act in larval germ line development. Genetic analysis supports roles for vit-1 and vit-3 in a linear pathway with rict-1. Our results establish the C. elegans germ line as a fruitful model for investigating TORC2 and its connection to stem cells and lipid biology. Summary StatementRICT-1/Rictor in C. elegans promotes larval germline development via canonical TORC2 signaling, and intestinal RICT-1 acts via vitellogenins VIT-1 and VIT-3 to promote the establishment of the germline progenitor pool.

developmental biology↗

bioRxiv2021

Innexin function dictates the spatial relationship between distal somatic cells in the Caenorhabditis elegans gonad without impacting the germline stem cell pool

Gap-junctional signaling mediates myriad cellular interactions in metazoans. Yet, how gap junctions control the positioning of cells in organs is not well understood. Innexins compose gap junctions in invertebrates and affect organ architecture. Here, we investigate the roles of gap-junctions in controlling distal somatic gonad architecture and its relationship to underlying germline stem cells in Caenorhabditis elegans. We show that a reduction of soma-germline gap-junctional activity causes displacement of distal sheath cells (Sh1) towards the distal end of the gonad. We confirm, by live imaging, transmission electron microscopy, and antibody staining, that bare regions--lacking somatic gonadal cell coverage of germ cells--are present between the distal tip cell (DTC) and Sh1, and we show that an innexin fusion protein used in a prior study encodes an antimorphic gap junction subunit that mispositions Sh1. We determine that, contrary to the model put forth in the prior study based on this fusion protein, Sh1 mispositioning does not markedly alter the position of the borders of the stem cell pool nor of the progenitor cell pool. Together, these results demonstrate that gap junctions can control the position of Sh1, but that Sh1 position is neither relevant for GLP-1/Notch signaling nor for the exit of germ cells from the stem cell pool.

developmental biology↗

bioRxiv2021

Modeling the C. elegans Germline Stem Cell Genetic Network using Automated Reasoning

Computational methods and tools are a powerful complementary approach to experimental work for studying regulatory interactions in living cells and systems. We demonstrate the use of formal reasoning methods as applied to the Caenorhabditis elegans germ line, which is an accessible model system for stem cell research. The dynamics of the underlying genetic networks and their potential regulatory interactions are key for understanding mechanisms that control cellular decision-making between stem cells and differentiation. We model the "stem cell fate" versus entry into the "meiotic development" pathway decision circuit in the young adult germ line based on an extensive study of published experimental data and known/hypothesized genetic interactions. We apply a formal reasoning framework to derive predictive networks for control of differentiation. Using this approach we simultaneously specify many possible scenarios and experiments together with potential genetic interactions, and synthesize genetic networks consistent with all encoded experimental observations. In silico analysis of knock-down and overexpression experiments within our model recapitulate published phenotypes of mutant animals and can be applied to make predictions on cellular decision-making. This work lays a foundation for developing realistic whole tissue models of the C. elegans germ line where each cell in the model will execute a synthesized genetic network.

systems biology↗

bioRxiv2021

Microbial byproducts determine reproductive fitness of free-living and parasitic nematodes

A distinguishing feature of Trichuris nematodes is that these parasitic worms reproduce within the digestive tracts of humans and other mammalian hosts shedding thousands of eggs daily, facilitating their sustained presence in the environment and hampering eradication efforts. Although this aspect of the lifecycle places Trichuris in a microbiota-rich environment, metabolic byproducts of bacteria that facilitate the reproductive development of parasites are unknown. Here, we employ a pipeline using the well-characterized free-living nematode C. elegans to identify microbial factors with conserved roles in the reproduction of nematodes. A screen for E. coli mutants that impair C. elegans fertility identified genes in fatty acid biosynthesis and ethanolamine utilization pathways, including fabH and eutN. Trichuris muris eggs displayed defective hatching in the presence of E. coli deficient in fabH or eutN due to reduction in arginine or elevated levels of aldehydes, respectively. Remarkably, T. muris reared in gnotobiotic mice colonized with these E. coli mutants displayed profound abnormalities including morphological defects and a failure to lay viable eggs. These findings indicate that microbial byproducts mediate evolutionarily conserved transkingdom interactions that impact the reproductive fitness of distantly-related nematodes.

microbiology↗

bioRxiv2020

DAF-18/PTEN inhibits germline zygotic gene activation during primordial germ cell quiescence

Quiescence, an actively-maintained reversible state of cell cycle arrest, is not well understood. PTEN is one of the most frequently lost tumor suppressors in human cancers and regulates quiescence of stem cells and cancer cells. In C. elegans mutant for daf-18, the sole C. elegans PTEN ortholog, primordial germ cells (PGCs) divide inappropriately in starvation conditions, in a TOR-dependent manner. Here, we further investigated the role of daf-18 in maintaining PGC quiescence. We found that maternal or zygotic daf-18 is sufficient to maintain cell cycle quiescence, that daf-18 acts in the germ line and soma, and that daf-18 affects timing of PGC divisions in fed animals. Importantly, our results also implicate daf-18 in zygotic germline gene activation, though not in germline fate specification. However, TOR is less important to zygotic germline gene expression, suggesting that in the absence of food daf-18/PTEN prevents inappropriate germline zygotic gene activation and cell division by distinct mechanisms.

developmental biology↗

bioRxiv2018

Intergenerational effects of dietary restriction on insulin/IGF signaling and reproductive development

The roundworm C. elegans transiently arrests larval development to survive extended starvation (1), but such early-life starvation reduces reproductive success (2, 3). Maternal dietary restriction (DR) buffers progeny from starvation, increasing reproductive success (4). It is unknown why early-life starvation decreases reproductive success and how maternal diet modifies this process. We show here that extended starvation in first-stage (L1) larvae followed by unrestricted feeding results in a variety of abnormalities in the reproductive system, including glp-1/Notch-sensitive germ-cell tumors and uterine masses that express neuronal and epidermal markers. We found that maternal DR reduces the penetrance of starvation-induced abnormalities, including tumors. Furthermore, we show that maternal DR reduces insulin/IGF signaling (IIS) in progeny, and that daf-16/FoxO and skn-1/Nrf, transcriptional effectors of IIS, are required in progeny for maternal DR to suppress abnormalities. daf-16/FoxO activity in somatic tissues is sufficient to suppress starvation-induced abnormalities, suggesting cell-nonautonomous regulation of reproductive system development. This work reveals complex inter- and intra-generational effects of nutrient availability mediated by IIS with consequences on developmental integrity and reproductive success.\n\nOne Sentence SummaryIntergenerational effects of diet on IIS

developmental biology↗