split-luciferase-reassembly-assay-to-measure-endoplasmic-reticulum

Split-Luciferase Reassembly Assay to Measure Endoplasmic Reticulum-Mitochondria Contacts in Live Cells

Endoplasmic reticulum (ER)-mitochondria contact sites play a critical role in cell health and homeostasis, such as the regulation of Ca2+ and lipid ...

Cedars-Sinai Medical Center

Interactions between the endoplasmic reticulum (ER) and mitochondria (Mito) are crucial for many cellular functions, and their interaction levels change dynamically depending on the cellular environment. Little is known about how the interactions between these organelles are regulated within the cell. Here we screened a compound library to identify chemical modulators for ER-Mito contacts in HEK293T cells. Multiple agonists of G-protein coupled receptors (GPCRs), beta-adrenergic receptors (β-ARs) in particular, scored in this screen. Analyses in multiple orthogonal assays validated that β2-AR activation promotes physical and functional interactions between the two organelles. Furthermore, we have elucidated potential downstream effectors mediating β2-AR-induced ER-Mito contacts. Together our study identifies β2-AR signaling as an important regulatory pathway for ER-Mito coupling and highlights the role of these contacts in responding to physiological demands or stresses.

β2-adrenergic receptor regulates ER-mitochondria contacts.

The Aristaless-related homeobox (ARX) is a paired-like homeodomain transcription factor playing important roles in brain development. Patients with mutations in ARX have a spectrum of neurodevelopmental disorders such as epilepsy, intellectual disability, and autism spectrum disorder, with or without structural abnormalities of the brain such as lissencephaly (smooth brain), microcephaly (small brain), and/or agenesis of the corpus callosum. Mouse models have provided important clues on the pathophysiologic roles of ARX in these disorders. However, successfully isolating specific in vivo complexes of ARX, with DNA and proteins, has remained as a challenge. To facilitate in vivo detection of ARX complexes, we generated a mouse line containing one epitope of FLAG-tag (1 × FLAG) targeted at the translational start site of the endogenous Arx gene using CRSPR/Cas9 strategy. Homozygous Flag-Arx mice are viable and fertile without gross abnormality, suggesting that the FLAG-tag does not perturb the normal function of ARX. Using a FLAG antibody, we successfully detected ARX with immunofluorescent staining and pulled down ARX in embryonic brain tissues. This Flag-Arx mouse line will be a useful tool to isolate ARX complexes from mouse tissues for many applications.

Generation of FLAG-tagged Arx knock-in mouse model.

Allele-specific PCR (AS-PCR) has been used as a simple, cost-effective method for genotyping and gene mapping in research and clinical settings. AS-PCR permits the detection of single nucleotide variants and insertion or deletion variants owing to the selective extension of a perfectly matched primer (to the template DNA) over a mismatched primer. Thus, the mismatch discrimination power of the DNA polymerase is critical. Unfortunately, currently available polymerases often amplify some mismatched primer-template complexes as well as matched ones, obscuring AS detection. To increase mismatch discrimination, mutations were generated in the Thermus aquaticus (Taq) DNA polymerase, the most efficient variant was selected, and its performance evaluated in single nucleotide polymorphism and cancer mutation genotyping. In addition, the primer design and reaction buffer conditions were optimized for AS amplification. Our highly selective AS-PCR, which is based on an allele-discriminating priming system that leverages a Taq DNA polymerase variant with optimized primers and reaction buffer, can detect mutations with a mutant allele frequency as low as 0.01% in genomic DNA and 0.0001% in plasmid DNA. This method serves as a simple, fast, cost-effective, and ultra-sensitive way to detect single nucleotide variants and insertion or deletion mutations with low abundance.

Modified Taq DNA Polymerase for Allele-Specific Ultra-Sensitive Detection of Genetic Variants.

Sonic hedgehog signaling regulates processes of embryonic development across multiple tissues, yet factors regulating context-specific Shh signaling remain poorly understood. Exome sequencing of families with polymicrogyria (disordered cortical folding) revealed multiple individuals with biallelic deleterious variants in , which encodes a multi-pass transmembrane protein of unknown function.  null mice demonstrated holoprosencephaly, craniofacial midline defects, eye defects, and spinal cord patterning changes consistent with impaired Shh signaling, but were without limb defects, suggesting a CNS-specific role of Tmem161b.  depletion impaired the response to Smoothened activation in vitro and disrupted cortical histogenesis in vivo in both mouse and ferret models, including leading to abnormal gyration in the ferret model. Tmem161b localizes non-exclusively to the primary cilium, and scanning electron microscopy revealed shortened, dysmorphic, and ballooned ventricular zone cilia in the  null mouse, suggesting that the Shh-related phenotypes may reflect ciliary dysfunction. Our data identify  as a regulator of cerebral cortical gyration, as involved in primary ciliary structure, as a regulator of Shh signaling, and further implicate Shh signaling in human gyral development.

Article	Year
β2-adrenergic receptor regulates ER-mitochondria contacts. Scientific reports\| PubMed ID: 34728663	2021
Generation of FLAG-tagged Arx knock-in mouse model. Genesis (New York, N.Y. : 2000)\| PubMed ID: 35656878	2022
Modified Taq DNA Polymerase for Allele-Specific Ultra-Sensitive Detection of Genetic Variants. The Journal of molecular diagnostics : JMD\| PubMed ID: 36058471	2022
TMEM161B regulates cerebral cortical gyration, Sonic Hedgehog signaling, and ciliary structure in the developing central nervous system. Proceedings of the National Academy of Sciences of the United States of America\| PubMed ID: 36669111	2023

Ginam Cho

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