Published: August 18th, 2013
Here we describe an effective method for studying dynamics of apoptotic cell clearance in vivo. This method employs live Drosophila embryos as a powerful model for monitoring phagocytosis of apoptotic cells using specific labeling of apoptotic cells and phagocytes.
The proper elimination of unwanted or aberrant cells through apoptosis and subsequent phagocytosis (apoptotic cell clearance) is crucial for normal development in all metazoan organisms. Apoptotic cell clearance is a highly dynamic process intimately associated with cell death; unengulfed apoptotic cells are barely seen in vivo under normal conditions. In order to understand the different steps of apoptotic cell clearance and to compare 'professional' phagocytes - macrophages and dendritic cells to 'non-professional' - tissue-resident neighboring cells, in vivo live imaging of the process is extremely valuable. Here we describe a protocol for studying apoptotic cell clearance in live Drosophila embryos. To follow the dynamics of different steps in phagocytosis we use specific markers for apoptotic cells and phagocytes. In addition, we can monitor two phagocyte systems in parallel: 'professional' macrophages and 'semi-professional' glia in the developing central nervous system (CNS). The method described here employs the Drosophila embryo as an excellent model for real time studies of apoptotic cell clearance.
The proper elimination of unwanted or aberrant cells through apoptosis and subsequent phagocytosis is crucial for embryonic development as well as for tissue homeostasis in the adult. Phagocytosis of apoptotic cells or apoptotic cell clearance is a highly dynamic process which proceeds in four steps: (1) recruitment of phagocytes to the apoptotic cell ('find-me'), (2) recognition of the cell as a target for phagocytosis ('eat-me') and (3) engulfment, followed by (4) phagosome maturation and degradation of the apoptotic particle1-5. There are two types of phagocytes: 'professional' macrophages and immature dendritic....
To follow the dynamics of apoptotic cell clearance in vivo two populations of cells must be labeled: phagocytic cells and apoptotic cells.
To mark phagocytic cell populations we use a Drosophila line containing the simu-cytGFP marker, which labels exclusively phagocytic cells in the embryo: macrophages, glia and ectoderm8. One can use different markers for phagocytic cells, including lines containing a hemocyte-specific Gal4 driver (crq-Gal4) or g.......
Representative frames from a movie in which apoptotic cells are labeled with Annexin V, and glia, ectoderm and macrophages are labeled with simu-cytGFP are shown in Figure 2. Each frame is a projection of 3 slices 2 μm each.
The embryo of stage 15 is properly positioned showing the embryonic CNS in the middle with well labeled glia (g). Macrophages (m), which are mostly outside the CNS, show strong cytoplasmic GFP expression. Ectodermal cells are also labeled.......
Apoptotic cell clearance is a critical last stage of apoptosis, which is highly dynamic. Therefore real time studies of the process are of utmost importance. Here we describe a protocol that enables monitoring of apoptotic cell clearance in living developing Drosophila embryos. In this procedure, two populations of cells must be marked using specific markers: apoptotic cells and phagocytes. The simu-cytGFP reporter is suitable for monitoring phagocytic macrophages, glia and ectoderm simultaneously .......
This work was supported by a Marie Curie Reintegration Grant (IRG249084). We thank all members of the Kurant laboratory. We also thank E. Suss-Toby at the Interdepartmental Bioimaging facility for excellent technical support.....
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