Identification of two pathways mediating protein targeting from ER to lipid droplets”. Publisher's VersionAbstract. 9/15/2021. “
Pathways localizing proteins to their sites of action within a cell are essential for eukaryotic cell organization and function. Although mechanisms of protein targeting to many organelles have been defined, little is known about how proteins, such as key metabolic enzymes, target from the ER to cellular lipid droplets (LDs). Here, we identify two distinct pathways for ER-to-LD (ERTOLD) protein targeting: early ERTOLD, occurring during LD formation, and late ERTOLD, targeting mature LDs after their formation. By using systematic, unbiased approaches, we identified specific membrane-fusion machinery, including regulators, a tether, and SNARE proteins, that are required for late ERTOLD targeting. Components of this fusion machinery localize to LD-ER interfaces and appear to be organized at ER exit sites (ERES) to generate ER-LD membrane bridges. We also identified multiple cargoes for early and late ERTOLD. Collectively, our data provide a new model for how proteins target LDs from the ER.
Genome-wide in vitro and in vivo RNAi screens reveal Fer3 to be an important regulator of kkv transcription in Drosophila.” Insect Sci.Abstract. 2021. “
Krotzkopf verkehrt (kkv) is a key enzyme that catalyzes the synthesis of chitin, an important component of the Drosophila epidermis, trachea, and other tissues. Here, we report the use of comprehensive RNA interference (RNAi) analyses to search for kkv transcriptional regulators. A cell-based RNAi screen identified 537 candidate kkv regulators on a genome-wide scale. Subsequent use of transgenic Drosophila lines expressing RNAi constructs enabled in vivo validation, and we identified six genes as potential kkv transcriptional regulators. Weakening of the kkvDsRed signal, an in vivo reporter indicating kkv promoter activity, was observed when the expression of Akirin, NFAT, 48 related 3 (Fer3), or Autophagy-related 101(Atg101) was knocked down in Drosophila at the 3rd-instar larval stage; whereas we observed disoriented taenidial folds on larval tracheae when Lines (lin) or Autophagy-related 3(Atg3) was knocked down in the tracheae. Fer3, in particular, has been shown to be an important factor in the activation of kkv transcription via specific binding with the kkv promoter. The genes involved in the chitin synthesis pathway were widely affected by the downregulation of Fer3. Furthermore, Atg101, Atg3, Akirin, Lin, NFAT, Pnr and Abd-A showed the potential complex mechanism of kkv transcription are regulated by an interaction network with bithorax complex components. Our study revealed the hitherto unappreciated diversity of modulators impinging on kkv transcription and opens new avenues in the study of kkv regulation and chitin biosynthesis. This article is protected by copyright. All rights reserved.
CRISPR-based engineering of gene knockout cells by homology-directed insertion in polyploid Drosophila S2R+ cells.” Nat Protoc, 15, 10, Pp. 3478-3498.Abstract. 2020. “
Precise and efficient genome modifications provide powerful tools for biological studies. Previous CRISPR gene knockout methods in cell lines have relied on frameshifts caused by stochastic insertion/deletion in all alleles. However, this method is inefficient for genes with high copy number due to polyploidy or gene amplification because frameshifts in all alleles can be difficult to generate and detect. Here we describe a homology-directed insertion method to knockout genes in the polyploid Drosophila S2R+ cell line. This protocol allows generation of homozygous mutant cell lines using an insertion cassette which autocatalytically generates insertion mutations in all alleles. Knockout cells generated using this method can be directly identified by PCR without a need for DNA sequencing. This protocol takes 2-3 months and can be applied to other polyploid cell lines or high-copy-number genes.
Use of the CRISPR-Cas9 System in Drosophila Cultured Cells to Introduce Fluorescent Tags into Endogenous Genes.” Curr Protoc Mol Biol, 130, 1, Pp. e112.Abstract. 2020. “
The CRISPR-Cas9 system makes it possible to cause double-strand breaks in specific regions, inducing repair. In the presence of a donor construct, repair can involve insertion or 'knock-in' of an exogenous cassette. One common application of knock-in technology is to generate cell lines expressing fluorescently tagged endogenous proteins. The standard approach relies on production of a donor plasmid with ∼500 to 1000 bp of homology on either side of an insertion cassette that contains the fluorescent protein open reading frame (ORF). We present two alternative methods for knock-in of fluorescent protein ORFs into Cas9-expressing Drosophila S2R+ cultured cells, the single-stranded DNA (ssDNA) Drop-In method and the CRISPaint universal donor method. Both methods eliminate the need to clone a large plasmid donor for each target. We discuss the advantages and limitations of the standard, ssDNA Drop-In, and CRISPaint methods for fluorescent protein tagging in Drosophila cultured cells. © 2019 by John Wiley & Sons, Inc. Basic Protocol 1: Knock-in into Cas9-positive S2R+ cells using the ssDNA Drop-In approach Basic Protocol 2: Knock-in into Cas9-positive S2R+ cells by homology-independent insertion of universal donor plasmids that provide mNeonGreen (CRISPaint method) Support Protocol 1: sgRNA design and cloning Support Protocol 2: ssDNA donor synthesis Support Protocol 3: Transfection using Effectene Support Protocol 4: Electroporation of S2R+-MT::Cas9 Drosophila cells Support Protocol 5: Single-cell isolation of fluorescent cells using FACS.
Pooled CRISPR Screens in Drosophila Cells.” Curr Protoc Mol Biol, 129, 1, Pp. e111.Abstract. 2019. “
High-throughput screens in Drosophila melanogaster cell lines have led to discovery of conserved gene functions related to signal transduction, host-pathogen interactions, ion transport, and more. CRISPR/Cas9 technology has opened the door to new types of large-scale cell-based screens. Whereas array-format screens require liquid handling automation and assay miniaturization, pooled-format screens, in which reagents are introduced at random and in bulk, can be done in a standard lab setting. We provide a detailed protocol for conducting and evaluating genome-wide CRISPR single guide RNA (sgRNA) pooled screens in Drosophila S2R+ cultured cells. Specifically, we provide step-by-step instructions for library design and production, optimization of cytotoxin-based selection assays, genome-scale screening, and data analysis. This type of project takes ∼3 months to complete. Results can be used in follow-up studies performed in vivo in Drosophila, mammalian cells, and/or other systems. © 2019 by John Wiley & Sons, Inc. Basic Protocol: Pooled-format screening with Cas9-expressing Drosophila S2R+ cells in the presence of cytotoxin Support Protocol 1: Optimization of cytotoxin concentration for Drosophila cell screening Support Protocol 2: CRISPR sgRNA library design and production for Drosophila cell screening Support Protocol 3: Barcode deconvolution and analysis of screening data.
HIF-independent synthetic lethality between CDK4/6 inhibition and VHL loss across species.” Sci Signal, 12, 601.Abstract. 2019. “
Inactivation of the tumor suppressor gene is the signature initiating event in clear cell renal cell carcinoma (ccRCC), the most common form of kidney cancer, and causes the accumulation of hypoxia-inducible factor 2α (HIF-2α). HIF-2α inhibitors are effective in some ccRCC cases, but both de novo and acquired resistance have been observed in the laboratory and in the clinic. Here, we identified synthetic lethality between decreased activity of cyclin-dependent kinases 4 and 6 (CDK4/6) and inactivation in two species (human and ) and across diverse human ccRCC cell lines in culture and xenografts. Although HIF-2α transcriptionally induced the CDK4/6 partner cyclin D1, HIF-2α was not required for the increased CDK4/6 requirement of ccRCC cells. Accordingly, the antiproliferative effects of CDK4/6 inhibition were synergistic with HIF-2α inhibition in HIF-2α-dependent ccRCC cells and not antagonistic with HIF-2α inhibition in HIF-2α-independent cells. These findings support testing CDK4/6 inhibitors as treatments for ccRCC, alone and in combination with HIF-2α inhibitors.
2018 Dec 08
Genome-wide RNAi screening implicates the E3 ubiquitin ligase Sherpa in mediating innate immune signaling by Toll in Drosophila adults.” Sci Signal, 8, 400, Pp. ra107.Abstract. 2015. “
The Drosophila Toll pathway plays important roles in innate immune responses against Gram-positive bacteria and fungi. To identify previously uncharacterized components of this pathway, we performed comparative, ex vivo, genome-wide RNA interference screening. In four screens, we overexpressed the Toll adaptor protein dMyd88, the downstream kinase Pelle, or the nuclear factor κB (NF-κB) homolog Dif, or we knocked down Cactus, the Drosophila homolog of mammalian inhibitor of NF-κB. On the basis of these screens, we identified the E3 ubiquitin ligase Sherpa as being necessary for the activation of Toll signaling. A loss-of-function sherpa mutant fly exhibited compromised production of antimicrobial peptides and enhanced susceptibility to infection by Gram-positive bacteria. In cultured cells, Sherpa mediated ubiquitylation of dMyd88 and Sherpa itself, and Sherpa and Drosophila SUMO (small ubiquitin-like modifier) were required for the proper membrane localization of an adaptor complex containing dMyd88. These findings highlight a role for Sherpa in Drosophila host defense and suggest the SUMOylation-mediated regulation of dMyd88 functions in Toll innate immune signaling.
Ex vivo genome-wide RNAi screening of the Drosophila Toll signaling pathway elicited by a larva-derived tissue extract.” Biochem Biophys Res Commun, 467, 2, Pp. 400-6.Abstract. 2015. “
Damage-associated molecular patterns (DAMPs), so-called "danger signals," play important roles in host defense and pathophysiology in mammals and insects. In Drosophila, the Toll pathway confers damage responses during bacterial infection and improper cell-fate control. However, the intrinsic ligands and signaling mechanisms that potentiate innate immune responses remain unknown. Here, we demonstrate that a Drosophila larva-derived tissue extract strongly elicits Toll pathway activation via the Toll receptor. Using this extract, we performed ex vivo genome-wide RNAi screening in Drosophila cultured cells, and identified several signaling factors that are required for host defense and antimicrobial-peptide expression in Drosophila adults. These results suggest that our larva-derived tissue extract contains active ingredients that mediate Toll pathway activation, and the screening data will shed light on the mechanisms of damage-related Toll pathway signaling in Drosophila.
2018 May 19