Biology subjects

Sun, J. L.

Publications and source records attributed to Sun, J. L..

5 recordsLinked to original sources

bioRxiv2025

Glutamate indicators with increased sensitivity and tailored deactivation rates

Identifying the input-output operations of neurons requires measurements of synaptic transmission simultaneously at many of a neurons thousands of inputs in the intact brain. To facilitate this goal, we engineered and screened 3365 variants of the fluorescent protein glutamate indicator iGluSnFR3 in neuron culture, and selected variants in the mouse visual cortex. Two variants have high sensitivity, fast activation (< 2 ms) and deactivation times tailored for recording large populations of synapses (iGluSnFR4s, 153 ms) or rapid dynamics (iGluSnFR4f, 26 ms). By imaging action-potential evoked signals on axons and visually-evoked signals on dendritic spines, we show that iGluSnFR4s/4f primarily detect local synaptic glutamate with single-vesicle sensitivity. The indicators detect a wide range of naturalistic synaptic transmission, including in the vibrissal cortex layer 4 and in hippocampal CA1 dendrites. iGluSnFR4 increases the sensitivity and scale (4s) or speed (4f) of tracking information flow in neural networks in vivo.

neuroscience↗

bioRxiv2024

A Hybrid Type I and II Polyketide Synthases Yields Distinct Aromatic Polyketides

Bacterial aromatic polyketides are compounds with multiple aromatic rings synthesized by bacterial type II polyketide synthases (PKSs), some of which have been developed into clinical drugs. Compounds containing aromatic polyketides synthesized by a hybrid type I and type II PKSs are extremely rare. Here, we report the discovery of a gene cluster encoding both modular type I PKS, type II PKS and KAS III through extensive bioinformatics analysis, leading to the characterization of the hybrid polyketide, spirocycline A. The structure of spirocycline A is unprecedented among all aromatic polyketides, featuring a unique starter unit, four spirocycles, and forming a dimer. Biosynthetic studies indicate that the starter unit of this molecule is synthesized by type I PKS in collaboration with two trans-acting ketoreductase (KR) and enoylreductase (ER). It is then transferred by KAS III to the type II PKS system, which then synthesizes the tricyclic aromatic polyketide backbone. The subsequent formation of the spirocycle and dimerization is carried out by four redox enzymes encoded in the gene cluster. Overall, the discovery of spirocycline A provides a new approach for identifying novel aromatic polyketides and offers potential enzymatic tools for the bioengineering of these hybrid polyketides. Table of Contents O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=82 SRC="FIGDIR/small/610196v1_ufig1.gif" ALT="Figure 1"> View larger version (11K): org.highwire.dtl.DTLVardef@5a7efaorg.highwire.dtl.DTLVardef@14665d5org.highwire.dtl.DTLVardef@c7b8f2org.highwire.dtl.DTLVardef@3f1e6c_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2024

Metabolic control by the Bithorax Complex-Wnt signaling crosstalk in Drosophila

Adipocytes distributed throughout the body play crucial roles in lipid metabolism and energy homeostasis. Regional differences among adipocytes influence normal function and disease susceptibility, but the mechanisms driving this regional heterogeneity remain poorly understood. Here, we report a genetic crosstalk between the Bithorax Complex (BX-C) genes and Wnt/Wingless signaling that orchestrates regional differences among adipocytes in Drosophila larvae. Abdominal adipocytes, characterized by the exclusive expression of abdominal A (abd-A) and Abdominal B (Abd-B), exhibit distinct features compared to thoracic adipocytes, with Wnt signaling further amplifying these disparities. Depletion of BX-C genes in adipocytes reduces fat accumulation, delays larval-pupal transition, and eventually leads to pupal lethality. Depleting Abd-A or Abd-B reduces Wnt target gene expression, thereby attenuating Wnt signaling-induced lipid mobilization. Conversely, Wnt signaling stimulated abd-A transcription, suggesting a feedforward loop that amplifies the interplay between Wnt signaling and BX-C in adipocytes. These findings elucidate how the crosstalk between cell-autonomous BX-C gene expression and Wnt signaling define unique metabolic behaviors in adipocytes in different anatomical regions of fat body, delineating larval adipose tissue domains.

developmental biology↗

bioRxiv2024

Distinct effects of CDK8 module subunits on cellular growth and proliferation in Drosophila

The Mediator complex, composed of about 30 conserved subunits, plays a pivotal role in facilitating RNA polymerase II-dependent transcription in eukaryotes. Within this complex, the CDK8 kinase module (CKM), comprising Med12, Med13, CDK8, and CycC (Cyclin C), serves as a dissociable subcomplex that modulates the activity of the small Mediator complex. Genetic studies in Drosophila have revealed distinct phenotypes of CDK8-CycC and Med12-Med13 mutations, yet the underlying mechanism has remained unknown. Here, using Drosophila as a model organism, we show that depleting CDK8-CycC enhances E2F1 target gene expression and promotes cell-cycle progression. Conversely, depletion of Med12-Med13 affects the expression of ribosomal protein genes and fibrillarin, indicating a more severe reduction in ribosome biogenesis and cellular growth compared to the loss of CDK8-CycC. Moreover, we found that the stability of CDK8 and CycC relies on Med12 and Med13, with a mutually interdependent relationship between Med12 and Med13. Furthermore, CycC stability depends on the other three CKM subunits. These findings reveal distinct roles for CKM subunits in vivo, with Med12-Med13 disruption exerting a more pronounced impact on ribosome biogenesis and cellular growth compared to the loss of CDK8-CycC. SignificanceThe CDK8 kinase module (CKM), comprising CDK8, CycC, Med12, and Med13, is essential in the Mediator complex for RNA polymerase II-dependent transcription in eukaryotes. While expected to function jointly, CKM subunit mutations result in distinct phenotypes in Drosophila. This study investigates the mechanisms driving these differing effects. Our analysis reveals the role of Med12-Med13 pair in regulating ribosomal biogenesis and cellular growth, contrasting with the involvement of CDK8-CycC in E2F1-dependent cell-cycle progression. Additionally, an asymmetric interdependence in the stability of CDK8-CycC and Med12-Med13 was observed. CKM mutations or overexpression are associated with cancers and cardiovascular diseases. Our findings underscore the distinct impacts of CKM mutations on cellular growth and proliferation, advancing our understanding of their diverse consequences in vivo.

cell biology↗

bioRxiv2022

A novel prion strain is responsible for the first case of chronic wasting disease in Finnish moose

Concern is mounting over the global emergence, expanding host range, and uncertain zoonotic potential of chronic wasting disease (CWD), a fatal, infectious disease of cervids caused by prions. Our previous studies using genetically modified CWD-susceptible mice showed that Norwegian and North American CWD are caused by different prion strains. Here we investigated the properties of prions causing the first case of Finnish moose CWD. While Finnish and Norwegian moose CWD prions share characteristics that distinguish them from North American CWD including the inability to replicate in lymphoid tissues, common responses to variations at residue 226 of host prion protein, and overlapping central nervous system profiles, they also exhibit pronounced conformational variation which is consistent with strain differences between Finnish and Norwegian moose CWD. Our findings support the existence of a surprisingly diverse portfolio of emergent CWD strains in Nordic countries that is etiologically distinct from North American CWD. Summary linePrion strain properties from the first case of chronic wasting disease in a Finnish moose are similar but not identical to Norwegian cases, supporting a growing population of strains in Nordic countries.

microbiology↗