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Published on: May 27, 2011
Origin and differentiation of supernumerary midline glia in Drosophila embryos deficient for apoptosis
1Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4K1, Canada.
Abstract:
Drosophila embryos deficient for programmed cell death produce 9 midline glia (MG) in addition to the wild-type complement of 3.2 MG/segment. More than 3 of the supernumerary MG derive from the MGP (MG posterior) lineage and the remainder from the MGA/MGM (MG anterior and middle) lineage. There is one unidentified additional neuron in the mesectoderm of embryos deficient for apoptosis. The supernumerary MG are not diverted from other lineages nor do they arise from an altered pattern of mitosis. Instead, these MG appear to arise from a normally existing pool of 12 precursor cells, larger than anticipated by earlier studies. During normal development, MG survival is dependent upon signaling to the Drosophila EGF receptor. The persistence of supernumerary MG in embryos deficient for apoptosis does not alter the spatial pattern of Drosophila EGF receptor signaling. The number and position of MG which express genes dependent upon EGF receptor function, such as pointed or argos, are indistinguishable from wild type. Genes of the spitz group are required for Drosophila EGF receptor function. Surviving MG in spitz group/H99 double mutants continue to express genes characteristic of the MG, but the cells fail to differentiate into ensheathing glia and are displaced from the nerve cord.
Insights
Programmed cell death normally eliminates excess midline glia (MG) precursors in Drosophila. Blocking apoptosis results in more MG, originating from a larger precursor pool, not altered mitosis or cell diversion.
Area of Science:
- Developmental Biology
- Neuroscience
- Cell Biology
Background:
- Midline glia (MG) are crucial for nervous system development in Drosophila.
- Cell death pathways regulate cell number during development.
- Drosophila EGF receptor signaling is essential for MG survival and differentiation.
Purpose of the Study:
- To investigate the role of programmed cell death in regulating the number of midline glia (MG) in Drosophila.
- To determine the origin of supernumerary MG when apoptosis is inhibited.
- To assess the impact of altered MG numbers on Drosophila EGF receptor signaling.
Main Methods:
- Analysis of programmed cell death-deficient Drosophila embryos.
- Lineage tracing to identify the origin of supernumerary MG.
- Gene expression analysis of MG markers and EGF receptor pathway components.
- Mutant analysis involving spitz group genes and H99 deficiency.
Main Results:
- Drosophila embryos lacking programmed cell death exhibit an increase in MG number, with supernumerary cells originating from both MGP and MGA/MGM lineages.
- The increased MG arise from a larger-than-anticipated precursor pool, not from altered mitosis or cell diversion.
- Drosophila EGF receptor signaling patterns remain unchanged in apoptosis-deficient embryos, with MG survival genes like pointed and argos expressed normally.
- In spitz group/H99 double mutants, surviving MG express MG-specific genes but fail to differentiate and are displaced from the nerve cord.
Conclusions:
- Programmed cell death is essential for limiting the number of midline glia (MG) in Drosophila.
- A larger precursor pool exists for MG development than previously thought.
- While EGF receptor signaling is necessary for MG differentiation, programmed cell death primarily controls MG cell numbers during development.
