A novel Cre/loxP system for mosaic gene expression in the Drosophila embryo

Using Drosophila melanogaster as a suitable platform for drug discovery from natural products in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic and life-treating inflammatory disease that can occur in multiple parts of the human intestine and has become a worldwide problem with a continually increasing incidence. Because of its mild early symptoms, most of them will not attract people's attention and may cause more serious consequences. There is an urgent need for new therapeutics to prevent disease progression. Natural products have a variety of active ingredients, diverse biological activities, and low toxicity or side effects, which are the new options for preventing and treating the intestinal inflammatory diseases. Because of multiple genetic models, less ethical concerns, conserved signaling pathways with mammals, and low maintenance costs, the fruit fly Drosophila melanogaster has become a suitable model for studying mechanism and treatment strategy of IBD. Here, we review the advantages of fly model as screening platform in drug discovery, describe the conserved molecular pathways as therapetic targets for IBD between mammals and flies, dissect the feasibility of Drosophila model in IBD research, and summarize the natural products for IBD treatment using flies. This review comprehensively elaborates that the benefit of flies as a perfact model to evaluate the therapeutic potential of phytochemicals against IBD.

Efficient allele conversion in mouse zygotes and primary cells based on electroporation of Cre protein

Cre-loxP recombination system is a powerful tool for genome engineering. One of its applications is found in genetic mouse models that often require to induce Cre recombination in preimplantation embryos. Here, we describe a technically simple, affordable and highly efficient protocol for Cre protein delivery into mouse zygotes by electroporation. We show that electroporation based delivery of Cre has no negative impact on embryo survival and the method can be easily combined with in vitro fertilization resulting in a significantly faster generation of desired models. Lastly, we demonstrate that Cre protein electroporation is suitable for allelic conversion in primary cells derived from conditional mouse models.

Drosophila Model in Cancer: An Introduction

Cancer is a cumulative manifestation of several complicated disease states that affect multiple organs. Over the last few decades, the fruit fly Drosophila melanogaster, has become a successful model for studying human cancers. The genetic simplicity and vast arsenal of genetic tools available in Drosophila provides a unique opportunity to address questions regarding cancer initiation and progression that would be extremely challenging in other model systems. In this chapter we provide a historical overview of Drosophila as a model organism for cancer research, summarize the multitude of genetic tools available, offer a brief comparison between different model organisms and cell culture platforms used in cancer studies and briefly discuss some of the latest models and concepts in recent Drosophila cancer research.

Enhanced TAT-Cre Protein Transduction for Efficient Gene Recombination in T cells

Genetic manipulation has increased our understanding of gene function and led to the discovery of new therapeutic targets. Cre/LoxP DNA recombination is widely used for genetic studies in mammalian cells. The direct delivery of Cre recombinase fused to protein transduction domains (PTDs), such as TAT, has been described as a valid alternative to the conditional, site-specific Cre expression in transgenic mice. However, efficiently conveying proteins into live cells, especially primary T cells, remains a major challenge. In this study, we show that one of our recently developed PTDs synthetic mimic greatly enhances the cellular uptake of the TAT-Cre fusion protein, enabling significantly smaller amounts of the protein to be used. We used this technique in primary mouse T cells to successfully delete, ex vivo, two essential genes involved in regulating T cell activation, Notch1 and Rbpjκ. Ex vivo gene deletion resulted in substantial protein reduction, comparable to that obtained in vivo when Cre-expressing Notch1-floxed (MxCre^±Notch1^fl/fl) mice were treated with polyinosinic-polycytidylic acid (polyl/C), but in considerably less time, and without altering normal cell physiology. These results highlight several key advantages that include the ability to use less expensive protein (TAT-Cre), a major reduction in total experimental time and labor, and fewer side effects on the treated cells. This method should offer new opportunities for immunological studies, especially in the context of identifying novel therapeutic targets.

Engineering the Drosophila Genome for Developmental Biology

The recent development of transposon and CRISPR-Cas9-based tools for manipulating the fly genome in vivo promises tremendous progress in our ability to study developmental processes. Tools for introducing tags into genes at their endogenous genomic loci facilitate imaging or biochemistry approaches at the cellular or subcellular levels. Similarly, the ability to make specific alterations to the genome sequence allows much more precise genetic control to address questions of gene function.

Genome engineering: Drosophila melanogaster and beyond

A central challenge in investigating biological phenomena is the development of techniques to modify genomic DNA with nucleotide precision that can be transmitted through the germ line. Recent years have brought a boon in these technologies, now collectively known as genome engineering. Defined genomic manipulations at the nucleotide level enable a variety of reverse engineering paradigms, providing new opportunities to interrogate diverse biological functions. These genetic modifications include controlled removal, insertion, and substitution of genetic fragments, both small and large. Small fragments up to a few kilobases (e.g., single nucleotide mutations, small deletions, or gene tagging at single or multiple gene loci) to large fragments up to megabase resolution can be manipulated at single loci to create deletions, duplications, inversions, or translocations of substantial sections of whole chromosome arms. A specialized substitution of chromosomal portions that presumably are functionally orthologous between different organisms through syntenic replacement, can provide proof of evolutionary conservation between regulatory sequences. Large transgenes containing endogenous or synthetic DNA can be integrated at defined genomic locations, permitting an alternative proof of evolutionary conservation, and sophisticated transgenes can be used to interrogate biological phenomena. Precision engineering can additionally be used to manipulate the genomes of organelles (e.g., mitochondria). Novel genome engineering paradigms are often accelerated in existing, easily genetically tractable model organisms, primarily because these paradigms can be integrated in a rigorous, existing technology foundation. The Drosophila melanogaster fly model is ideal for these types of studies. Due to its small genome size, having just four chromosomes, the vast amount of cutting-edge genetic technologies, and its short life-cycle and inexpensive maintenance requirements, the fly is exceptionally amenable to complex genetic analysis using advanced genome engineering. Thus, highly sophisticated methods developed in the fly model can be used in nearly any sequenced organism. Here, we summarize different ways to perform precise inheritable genome engineering using integrases, recombinases, and DNA nucleases in the D. melanogaster. For further resources related to this article, please visit the WIREs website.

Left-right asymmetry is formed in individual cells by intrinsic cell chirality

Many animals show left-right (LR) asymmetric morphology. The mechanisms of LR asymmetric development are evolutionarily divergent, and they remain elusive in invertebrates. Various organs in Drosophila melanogaster show stereotypic LR asymmetry, including the embryonic gut. The Drosophila embryonic hindgut twists 90° left-handedly, thereby generating directional LR asymmetry. We recently revealed that the hindgut epithelial cell is chiral in shape and other properties; this is termed planar cell chirality (PCC). We previously showed by computer modeling that PCC is sufficient to induce the hindgut rotation. In addition, both the PCC and the direction of hindgut twisting are reversed in Myosin31DF (Myo31DF) mutants. Myo31DF encodes Drosophila MyosinID, an actin-based motor protein, whose molecular functions in LR asymmetric development are largely unknown. Here, to understand how PCC directs the asymmetric cell-shape, we analyzed PCC in genetic mosaics composed of cells homozygous for mutant Myo31DF, some of which also overexpressed wild-type Myo31DF. Wild-type cell-shape chirality only formed in the Myo31DF-overexpressing cells, suggesting that cell-shape chirality was established in each cell and reflects intrinsic PCC. A computer model recapitulating the development of this genetic mosaic suggested that mechanical interactions between cells are required for the cell-shape behavior seen in vivo. Our mosaic analysis also suggested that during hindgut rotation in vivo, wild-type Myo31DF suppresses the elongation of cell boundaries, supporting the idea that cell-shape chirality is an intrinsic property determined in each cell. However, the amount and distribution of F-actin and Myosin II, which are known to help generate the contraction force on cell boundaries, did not show differences between Myo31DF mutant cells and wild-type cells, suggesting that the static amount and distribution of these proteins are not involved in the suppression of cell-boundary elongation. Taken together, our results suggest that cell-shape chirality is intrinsically formed in each cell, and that mechanical force from intercellular interactions contributes to its formation and/or maintenance.

Controlled Cre/loxP site-specific recombination in the developing brain in medaka fish, Oryzias latipes

Background

Genetic mosaic techniques have been used to visualize and/or genetically modify a neuronal subpopulation within complex neural circuits in various animals. Neural populations available for mosaic analysis, however, are limited in the vertebrate brain.

Methodology/Principal Findings

To establish methodology to genetically manipulate neural circuits in medaka, we first created two transgenic (Tg) medaka lines, Tg (HSP:Cre) and Tg (HuC:loxP-DsRed-loxP-GFP). We confirmed medaka HuC promoter-derived expression of the reporter gene in juvenile medaka whole brain, and in neuronal precursor cells in the adult brain. We then demonstrated that stochastic recombination can be induced by micro-injection of Cre mRNA into Tg (HuC:loxP-DsRed-loxP-GFP) embryos at the 1-cell stage, which allowed us to visualize some subpopulations of GFP-positive cells in compartmentalized regions of the telencephalon in the adult medaka brain. This finding suggested that the distribution of clonally-related cells derived from single or a few progenitor cells was restricted to a compartmentalized region. Heat treatment of Tg(HSP:Cre x HuC:loxP-DsRed-loxP-GFP) embryos (0–1 day post fertilization [dpf]) in a thermalcycler (39°C) led to Cre/loxP recombination in the whole brain. The recombination efficiency was notably low when using 2–3 dpf embyos compared with 0–1 dpf embryos, indicating the possibility of stage-dependent sensitivity of heat-inducible recombination. Finally, using an infrared laser-evoked gene operator (IR-LEGO) system, heat shock induced in a micro area in the developing brains led to visualization of clonally-related cells in both juvenile and adult medaka fish.

Conclusions/Significance

We established a noninvasive method to control Cre/loxP site-specific recombination in the developing nervous system in medaka fish. This method will broaden the neural population available for mosaic analyses and allow for lineage tracing of the vertebrate nervous system in both juvenile and adult stages.