Drosophila As a Cancer Model

Abstract

Over the last few decades, Drosophila cancer models have made great contributions to our understanding toward fundamental cancer processes. Particularly, the development of genetic mosaic technique in Drosophila has enabled us to recapitulate basic aspects of human cancers, including clonal evolution, tumor microenvironment, cancer cachexia, and anticancer drug resistance. The mosaic technique has also led to the discovery of important tumor-suppressor pathways such as the Hippo pathway and the elucidation of the mechanisms underlying tumor growth and metastasis via regulation of cell polarity, cell-cell cooperation, and cell competition. Recent approaches toward identification of novel therapeutics using fly cancer models have further proved Drosophila as a robust system with great potentials for cancer research as well as anti-cancer therapy.

Enomoto M. and Siow C. are equally contributed.

Commonly Used Protocol

Protocol I

MARCM technique used in Drosophila cancer models. (a) The MARCM technique allows expression of target transgenes coupled with GFP specifically in clones. The parental cell contains chromosomes with homologous FRT sequence located at the same position, heterozygous Gal80 controlled by ubiquitous promoter tubP located at a distal site from FRT, heterozygous mutation (denoted as *) distal to FRT but in trans to Gal80 chromosome, and FLP sequence controlled by eyP specific to the eye-antennal imaginal discs (EAD). The Gal4/UAS system is governed by ubiquitous promoter actP with a y spacer tagged downstream with a UAS-GFP marker sequence. The y spacer includes a transcriptional stop codon so that prior to activation of the FLP recombinase (and subsequent FLP-out), the gene downstream (UAS-GFP) of the spacer is not transcribed. After DNA replication , FLP expressed specifically in the EAD mediates mitotic recombination at FRT sites (arrows) and concurrently allows FLP-out of the y spacer. Three types of distinct progeny (as mosaics in an EAD tissue) can be produced after mitosis and cell division, in which cells with one/two copies of Gal80 are unlabeled as wild type, while cells without Gal80 is homozygous for the mutation and are labeled with GFP fluorescence. Fluorescently labeled transgenic cells are a result of the loss of GAL80 repression on GAL4, thus allowing GAL4 to drive expression of any other UAS transgenes. (b) An example of a confocal image showing wt//wt or wts ^−/−//wt EAD mosaics generated by MARCM. Cell nuclei are stained with DAPI (blue). DAPI, 4,6-diamidino-2-phenylindole; GFP, green fluorescent protein; actP, actin promoter; tubP, tubulin promoter; eyP, eyeless promoter; FLP, flippase; FRT, flippase recognition target; wt, wild type.

Protocol II

The process of malignant transformation and Drosophila model of tumor progression. (a) General scheme illustrating autonomous malignant transformation of Ras ^V12 mutant subclones in a tissue after acquiring sequential mutation, e.g., scrib ^−/−. (b) Schematic drawing showing an EAD mosaic in a scrib ^−/− + Ras ^V12 mutant larva generated by eyFLP-MARCM technique. Green spots depicted are GFP-labeled patches of scrib ^−/− + Ras ^V12 mutant clones surrounded by unlabeled wild-type cells in the EAD attached to the brain-VNC complex. Over time, scrib ^−/− + Ras ^V12 mutant cells acquire malignant behavior and invade to adjacent ventral nerve code (VNC). Overgrowth of scrib ^−/− + Ras ^V12 clones outcompetes wt subclones, as shown by an increase in GFP-labeled mutants and a decrease in unlabeled wt cells.