Biology subjects

Tomlinson, A.

Publications and source records attributed to Tomlinson, A..

8 recordsLinked to original sources

bioRxiv2026

Molecularly defined subpopulations of leptin receptor neurons dissociate the control of food intake from blood pressure

While previous studies have suggested that leptin regulates cardiovascular function independently of body weight, the specific leptin receptor (Lepr)-expressing neurons that mediate these distinct effects remain unknown. We found that genes located in blood pressure (BP)-associated genome-wide association study loci were regulated by leptin in Lepr and glucagon-like peptide-1 receptor (Glp1r)-expressing (LeprGlp1r) neurons. Ablating Lepr from these cells decreased BP despite causing hyperphagic obesity. Single-cell and spatial transcriptomics revealed that LeprGlp1r neurons segregate into two distinct subpopulations of cells located in the arcuate nucleus (ARC) and dorsomedial hypothalamic nucleus (DMH). Activating ARC LeprGlp1r neurons suppressed food intake without impacting energy expenditure or cardiovascular function. Conversely, DMH LeprGlp1r neurons increased energy utilization and BP without altering food intake. Our results identify distinct LeprGlp1r neuron subpopulations that dissociate the control of food intake from outputs related to sympathetic tone, including BP, suggesting the potential therapeutic utility of targeting of these subpopulations independently.

physiology↗

bioRxiv2025

Sensory receptor expansion and neural accommodation in butterfly color vision

The evolution of complex brains required existing neurons and neural circuits to accommodate new inputs. The genetic and developmental mechanisms that enable such integration are largely unknown. Butterflies evolved more complex retinal mosaics through the addition of a second R7 color photoreceptor per ommatidium (unit eye). In Drosophila, the unique R7 makes a stochastic choice to express one of two opsin genes. In butterflies, the two R7s make independent stochastic cell fate choices in each ommatidium, producing three ommatidial types instead of two. Here, we investigate the developmental basis of this change and how the butterfly brain accommodates expanded sensory receptor input. We first identified the changes in gene expression that cause a second R7 cell to be specified. We then modified Drosophila retinas to have butterfly-like transcription factor expression, causing recruitment of an additional R7. The two R7s make independent stochastic choices, like butterflies, leading to three stochastically distributed ommatidial types. In Drosophila, the two R7 subtypes connect to their target neurons, either yDm8 or pDm8. Dm8 neurons of both types are born in excess and Dm8s that do not find connections with their cognate y or pR7s undergo apoptosis. In the presence of extra R7s in butterfly-like fly retinas, additional Dm8s are retained, leading to two Dm8s per medulla column that make appropriate connections with the matching R7 subtypes, facilitating the expansion of color vision. We propose that the presence of cells that would otherwise die provide developmental flexibility that can allow brains to accommodate newly evolved inputs.

developmental biology↗

bioRxiv2025

Genetic mechanisms of resistance to targeted KRAS inhibition

KRAS mutations are among the most prevalent oncogenic drivers in non-small cell lung cancer (NSCLC), yet the mechanisms of therapeutic resistance to KRAS inhibitors in these cancers remains poorly understood. Here, we deploy high-throughput CRISPR base editing screens to systematically map resistance mutations to three mechanistically distinct KRAS-targeted therapies, including KRAS-G12C(OFF) inhibitor (adagrasib), RAS(ON) G12C-selective tri-complex inhibitor (RMC-4998), and RAS(ON) multi-selective tri-complex inhibitor (RMC-7977). Using both a saturation Kras tiling approach and cancer-associated mutation library, we identify common and compound-selective second-site resistance mutations in Kras, as well as gain-of-function and loss-of-function variants across cancer-associated genes that rewire signaling networks in a context-dependent manner. Notably, we identify a recurrent missense mutation in capicua (Cic), that promotes resistance to RMC-7977 in vitro and in vivo. Moreover, we show that targeting NF{kappa}B signaling in CIC-mutant cells can resensitize them to RAS pathway inhibition and overcome resistance.

cancer biology↗

bioRxiv2025

Neuronal SEL1L-HRD1 ERAD regulates one-carbon metabolism and is essential for motor function and survival

Hypomorphic variants in the SEL1L-HRD1 ER-associated degradation (ERAD) complex have been linked to severe neurological syndromes in children, including neurodevelopmental delay, intellectual disability, motor dysfunction, and early death. Despite this association, its physiological importance and underlying mechanisms in neurons remain poorly understood. Here, we show that neuronal SEL1L-HRD1 ERAD is essential for maintaining one-carbon metabolism, motor function, and overall viability. Neuron-specific deletion of Sel1L in mice (Sel1LSynCre) resulted in growth retardation, severe motor impairments, and early mortality by 9 weeks of age--mirroring core clinical features observed in affected patients--despite preserved neuronal numbers and only modest ER stress. Multi-omics analyses, including single-nucleus RNA sequencing and metabolomics, revealed significant dysregulation of one-carbon metabolism in ERAD-deficient brains. This included activation of the serine, folate, and methionine pathways, accompanied by elevated levels of S-adenosylmethionine and related metabolites, likely resulted from induction of the integrated stress response (ISR). Together, these findings uncover a previously unappreciated role for neuronal SEL1L-HRD1 ERAD in coordinating ER protein quality control with metabolic adaptation, providing new insight into the molecular basis of ERAD-related neurodevelopmental disease. SummaryUsing a neuron-specific Sel1L knockout mouse model, we demonstrate that Sel1L deficiency activates integrated stress responses, rewires one-carbon metabolism, and impairs motor function and survival.

cell biology↗

bioRxiv2025

Intracellular Trafficking SNARE Protein, Syntaxin-6, is a Modifier of Prion and Tau Pathogenesis in vivo and in Cellular Models

Syntaxin-6, a SNARE protein involved in intracellular protein trafficking, is a proposed risk factor for sporadic prion disease, progressive supranuclear palsy and Alzheimers disease. However, no study has validated its functional role in these diseases, explored the disease stage at which it is acting nor its mechanism of action. Here, we show that syntaxin-6 acts at early stages of prion disease in experimental mice by increasing disease transmission risk following inoculation with low prion doses. Conversely, syntaxin-6 does not affect prion propagation kinetics or toxicity during established disease. Syntaxin-6 manipulation in cellular models profoundly alters the subcellular distribution and morphologies of disease-related PrP and modifies prion export. Furthermore, syntaxin-6 knockout in a transgenic tauopathy mouse model exerts protective effects on numerous physiological, behavioural and neuropathological outcome measures. Therefore, our studies firmly establish syntaxin-6 as a modifier of prion and tau pathogenesis, providing key insights into a fundamental mechanism of neurodegeneration.

neuroscience↗

bioRxiv2025

Roles Played by Enhancer of Split Transcription Factors in Drosophila R7 Photoreceptor Specification

When a cell receives multiple developmental signals simultaneously, the intracellular transduction pathways triggered by those signals are coincidentally active. How then, do the cells decode the information contained within those multiple active pathways to derive a precise developmental directive? The specification of the Drosophila R7 photoreceptor is classic model system for investigating such questions. The R7 fate is specified by the combined actions of the of the Notch (N) and receptor tyrosine kinase (RTK) signaling pathways. The two pathways cross-communicate in an integrative mechanism but also supply information independently of each other. Collectively, this information is summed to provide an unambiguous directive for the R7 fate. Our goal is to understand these mechanisms. Here, we examine how N activity represses transcription of the phyllopod gene in the process of information integration with the RTK pathway, and how it represses expression of the seven-up gene in an independent mechanism needed for R7 fate. We describe how N activity achieves these transcriptional repressions, and identify Enhancer of Split transcription factors as the mediators of those actions. Summary StatementThis work examines the role played by Enhancer of Split transcription factors in mediating N signals in Drosophila R7 photoreceptor specification.

developmental biology↗

bioRxiv2024

Decoding a cell fate: How Notch and Receptor Tyrosine Kinase Signals Specify the Drosophila R7 Photoreceptor

The Drosophila R7 photoreceptor is a classic model for understanding how integration of signaling information can provide precise fate directives. It entails extensive interactions between the RTK and Notch signaling pathways, with Notch providing three distinct functions: it both opposes and promotes the general photoreceptor fate, and it determines the specific photoreceptor type. The RTK pathway promotes transcription of phyl - a gene expression critical for photoreceptor specification. We show that Notch activity induces transcription of yan which encodes a transcriptional repressor of phyl. This defines the antagonism between the two pathways, with RTK promoting and Notch opposing phyl transcription. We previously showed that Notch provides Sevenless to the cell to allow RTK pathway hyperactivation to overcome the Notch repression, and we now identify the regulation of Yan activity as the integration site of the RTK and Notch functions. Once the cell is specified as a photoreceptor, the third Notch function then prevents seven-up (svp) transcription. The Svp transcription factor directs the R1/6 photoreceptor fate, and the prevention of its expression ensures the default R7 specification. Summary StatementThis paper examines how the different signals received by the Drosophila R7 photoreceptor precursor are decoded and used to direct the cells appropriate differentiation pathway.

developmental biology↗

bioRxiv2019

The Role of Sevenless in Drosophila R7 Photoreceptor Specification

Sevenless (Sev) is a Receptor Tyrosine Kinase (RTK) that is required for the specification of the Drosophila R7 photoreceptor. Other Drosophila photoreceptors are specified by the action of another RTK; the Drosophila EGF Receptor (DER). Why Sev is required specifically in the R7 precursor, and the exact role it plays in the cells fate assignment have long remained unclear. Notch (N) signaling plays many roles in R7 specification, one of which is to prevent DER activity from establishing the photoreceptor fate. Our current model of Sev function is that it hyperactivates the RTK pathway in the R7 precursor to overcome in the N-imposed block on photoreceptor specification. From this perspective DER and Sev are viewed as engaging the same transduction machinery, the only difference between them being the level of pathway activation that they induce. To test this model, we generated a Sev/DER chimera in which the intracellular domain of Sev is replaced with that of DER. This chimerical receptor acts indistinguishably from Sev itself; a result that is entirely consistent with the two RTKs sharing identical transduction abilities. A long-standing question in regard to Sev is the function of a hydrophobic domain some 60 amino acids from the initiating Methionine. If this represents a transmembrane domain, it would endow Sev with N-terminal intracellular sequences through which it could engage internal transduction pathways. However, we find that this domain acts as an internal signal peptide, and that there is no Sev N-terminal intracellular domain. phyllopod (phyl) is the target gene of the RTK pathway, and we show that R7 precursors are selectively lost when phyl gene function is mildly compromised, and that other photoreceptors are removed when the gene function is further reduced. This result adds a key piece of evidence for the hyperactivation of the RTK pathway in the R7 precursor. To facilitate the hyperactivation of the RTK pathway, Sev is expressed at high levels. However, when we express DER at the levels at which Sev is expressed, strong gain-of-function effects result, consistent with ligand-independent activation of the receptor. This highlights another key feature of Sev; that it is expressed at high levels yet remains strictly ligand dependent. Finally, we find that activated Sev can rescue R3/4 photoreceptors when their DER function is abrogated. These results are collectively consistent with Sev and DER activating the same transduction machinery, with Sev generating a pathway hyperactivation to overcome the N-imposed block to photoreceptor specification in R7 precursors.

developmental biology↗