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Genetic control of astrocyte function in neural circuits.

Jahn HM, Scheller A, Kirchhoff F - Front Cell Neurosci (2015)

Bottom Line: Furthermore, such genetic approaches have also been used to restore astrocyte function.In these studies two alternatives were employed to achieve proper genetic targeting of astrocytes: transgenes using the promoter of the human glial fibrillary acidic protein (GFAP) or homologous recombination into the glutamate-aspartate transporter (GLAST) locus.We will highlight their specific properties that could be relevant for their use.

View Article: PubMed Central - PubMed

Affiliation: Molecular Physiology, Center for Integrative Physiology and Molecular Medicine (CIPMM), University of Saarland Homburg, Germany.

ABSTRACT
During the last two decades numerous genetic approaches affecting cell function in vivo have been developed. Current state-of-the-art technology permits the selective switching of gene function in distinct cell populations within the complex organization of a given tissue parenchyma. The tamoxifen-inducible Cre/loxP gene recombination and the doxycycline-dependent modulation of gene expression are probably the most popular genetic paradigms. Here, we will review applications of these two strategies while focusing on the interactions of astrocytes and neurons in the central nervous system (CNS) and their impact for the whole organism. Abolishing glial sensing of neuronal activity by selective deletion of glial transmitter receptors demonstrated the impact of astrocytes for higher cognitive functions such as learning and memory, or the more basic body control of muscle coordination. Interestingly, also interfering with glial output, i.e., the release of gliotransmitters can drastically change animal's physiology like sleeping behavior. Furthermore, such genetic approaches have also been used to restore astrocyte function. In these studies two alternatives were employed to achieve proper genetic targeting of astrocytes: transgenes using the promoter of the human glial fibrillary acidic protein (GFAP) or homologous recombination into the glutamate-aspartate transporter (GLAST) locus. We will highlight their specific properties that could be relevant for their use.

No MeSH data available.


Related in: MedlinePlus

Astrocyte heterogeneity and gene targeting strategies to influence astrocyte behavior. Throughout development and in different brain regions, the heterogeneity of astrocytes becomes rather obvious when looking at the different morphologies. It is more the cell volume with cytosol and cell membrane that helps to visualize astrocyte function rather than the cytoskeletal structure (A–F). Only few genetic strategies have been used to modify astrocyte function in vivo(G–J). (A) glial fibrillary acidic protein (GFAP)-stained acutely isolated astrocyte. (B) Cortical astrocytes expressing tdTomato in close contact to a blood vessel with their end feet, (C) Hippocampal astrocytes (CA1) expressing GFAP. (D) Single Bergmann glia (BG) cell with CreERT2/loxP controlled reporter expression (EGFP). (E) Cortical astrocyte expressing EGFP and surrounding a blood vessel. Scale bars: A,D,E = 10 μm, B = 20 μm, C = 50 μm. (F) Electron micrograph depicting the intimate enwrapping of pre- and postsynaptic terminals by astroglial processes (BG: Bergmann glial processes, scale bar: 1 μm). (G) Knock-in of CreERT2 into the GLAST locus leads to tamoxifen-sensitive recombination in all astrocytes with endogenous GLAST promoter activity (Mori et al., 2006). The DNA recombinase variant CreERT2 is trapped in the cytosol by heat shock proteins (HSP), after tamoxifen application the protein is released and translocated into the nucleus. (H,I) Transgenic GFAP-CreERT2 mice generated by non-homologous recombination can also be used to target astrocytes (Hirrlinger et al., 2006). The Cre/loxP system can either be used to selective excise gene alleles of interest (G,H; knockout) or to express genes of interest (e.g., reporter proteins such as GFP or genetically encoded Ca2+ indicators), but also to restore gene function (I) (Lioy et al., 2011). (J) Alternatively, the binary tTA/tetO system composed of (1) promoter-controlled expression of a tetracyclin transactivator protein; and (2) tetracycline/doxycycline-responsive elements driving the expression of proteins-of-interest (Pascual et al., 2005). This system allows for a certain degree of reversible gene regulation.
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Figure 1: Astrocyte heterogeneity and gene targeting strategies to influence astrocyte behavior. Throughout development and in different brain regions, the heterogeneity of astrocytes becomes rather obvious when looking at the different morphologies. It is more the cell volume with cytosol and cell membrane that helps to visualize astrocyte function rather than the cytoskeletal structure (A–F). Only few genetic strategies have been used to modify astrocyte function in vivo(G–J). (A) glial fibrillary acidic protein (GFAP)-stained acutely isolated astrocyte. (B) Cortical astrocytes expressing tdTomato in close contact to a blood vessel with their end feet, (C) Hippocampal astrocytes (CA1) expressing GFAP. (D) Single Bergmann glia (BG) cell with CreERT2/loxP controlled reporter expression (EGFP). (E) Cortical astrocyte expressing EGFP and surrounding a blood vessel. Scale bars: A,D,E = 10 μm, B = 20 μm, C = 50 μm. (F) Electron micrograph depicting the intimate enwrapping of pre- and postsynaptic terminals by astroglial processes (BG: Bergmann glial processes, scale bar: 1 μm). (G) Knock-in of CreERT2 into the GLAST locus leads to tamoxifen-sensitive recombination in all astrocytes with endogenous GLAST promoter activity (Mori et al., 2006). The DNA recombinase variant CreERT2 is trapped in the cytosol by heat shock proteins (HSP), after tamoxifen application the protein is released and translocated into the nucleus. (H,I) Transgenic GFAP-CreERT2 mice generated by non-homologous recombination can also be used to target astrocytes (Hirrlinger et al., 2006). The Cre/loxP system can either be used to selective excise gene alleles of interest (G,H; knockout) or to express genes of interest (e.g., reporter proteins such as GFP or genetically encoded Ca2+ indicators), but also to restore gene function (I) (Lioy et al., 2011). (J) Alternatively, the binary tTA/tetO system composed of (1) promoter-controlled expression of a tetracyclin transactivator protein; and (2) tetracycline/doxycycline-responsive elements driving the expression of proteins-of-interest (Pascual et al., 2005). This system allows for a certain degree of reversible gene regulation.

Mentions: Astrocytes represent an abundant, but also heterogeneous group of glial cells in all regions of the brain (Figures 1A–F). Their numerous interactions with capillaries and neurons are important signaling pathways for physiological brain function. Astrocytes actively control signal processing and transmission at the tripartite synapse (Perea et al., 2009). Originally, astrocytes were regarded as silent non-excitable cells, since they do not communicate via electrical signals. But now, it has become very clear that astroglial signaling is encoded in complex spatial and temporal patterns of Ca2+ changes within subcellular compartments as well as throughout cellular networks coupled by gap junctions. Intracellular Ca2+ rises indicate how they sense activity of their surroundings (Zorec et al., 2012; Araque et al., 2014; Verkhratsky and Parpura, 2014). Intracellular changes of another cation, Na+, have been recognized as an additional or alternative indicator of astrocyte activation (Kirischuk et al., 2012; Verkhratsky et al., 2013; Rose and Chatton, 2015). Even over longer distances astrocytes can convey various signals, e.g., inositol-1,4,5-trisphosphate (IP3) or cyclic nucleotides that pass through gap junctions and functionally couple the astroglial syncytium (Giaume and Liu, 2012; Theis and Giaume, 2012). Within these networks information spreads with tens of μm/s speed, still several orders of magnitude slower than the propagation of neuronal action potentials (Haydon and Nedergaard, 2015). The interactions of astrocytes with neurons are largely based on astroglial receptors that sense neuronal communication or on the release of gliotransmitters acting back on synaptic transmission. The general importance of astrocytes for brain function is uncovered by the devastating point mutations in single genes encoding transcription factors since these factors can control extended sets of gene programs. Genetically modified mice addressing astrocyte function have been instrumental in uncovering their role in the living animal.


Genetic control of astrocyte function in neural circuits.

Jahn HM, Scheller A, Kirchhoff F - Front Cell Neurosci (2015)

Astrocyte heterogeneity and gene targeting strategies to influence astrocyte behavior. Throughout development and in different brain regions, the heterogeneity of astrocytes becomes rather obvious when looking at the different morphologies. It is more the cell volume with cytosol and cell membrane that helps to visualize astrocyte function rather than the cytoskeletal structure (A–F). Only few genetic strategies have been used to modify astrocyte function in vivo(G–J). (A) glial fibrillary acidic protein (GFAP)-stained acutely isolated astrocyte. (B) Cortical astrocytes expressing tdTomato in close contact to a blood vessel with their end feet, (C) Hippocampal astrocytes (CA1) expressing GFAP. (D) Single Bergmann glia (BG) cell with CreERT2/loxP controlled reporter expression (EGFP). (E) Cortical astrocyte expressing EGFP and surrounding a blood vessel. Scale bars: A,D,E = 10 μm, B = 20 μm, C = 50 μm. (F) Electron micrograph depicting the intimate enwrapping of pre- and postsynaptic terminals by astroglial processes (BG: Bergmann glial processes, scale bar: 1 μm). (G) Knock-in of CreERT2 into the GLAST locus leads to tamoxifen-sensitive recombination in all astrocytes with endogenous GLAST promoter activity (Mori et al., 2006). The DNA recombinase variant CreERT2 is trapped in the cytosol by heat shock proteins (HSP), after tamoxifen application the protein is released and translocated into the nucleus. (H,I) Transgenic GFAP-CreERT2 mice generated by non-homologous recombination can also be used to target astrocytes (Hirrlinger et al., 2006). The Cre/loxP system can either be used to selective excise gene alleles of interest (G,H; knockout) or to express genes of interest (e.g., reporter proteins such as GFP or genetically encoded Ca2+ indicators), but also to restore gene function (I) (Lioy et al., 2011). (J) Alternatively, the binary tTA/tetO system composed of (1) promoter-controlled expression of a tetracyclin transactivator protein; and (2) tetracycline/doxycycline-responsive elements driving the expression of proteins-of-interest (Pascual et al., 2005). This system allows for a certain degree of reversible gene regulation.
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Related In: Results  -  Collection

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Figure 1: Astrocyte heterogeneity and gene targeting strategies to influence astrocyte behavior. Throughout development and in different brain regions, the heterogeneity of astrocytes becomes rather obvious when looking at the different morphologies. It is more the cell volume with cytosol and cell membrane that helps to visualize astrocyte function rather than the cytoskeletal structure (A–F). Only few genetic strategies have been used to modify astrocyte function in vivo(G–J). (A) glial fibrillary acidic protein (GFAP)-stained acutely isolated astrocyte. (B) Cortical astrocytes expressing tdTomato in close contact to a blood vessel with their end feet, (C) Hippocampal astrocytes (CA1) expressing GFAP. (D) Single Bergmann glia (BG) cell with CreERT2/loxP controlled reporter expression (EGFP). (E) Cortical astrocyte expressing EGFP and surrounding a blood vessel. Scale bars: A,D,E = 10 μm, B = 20 μm, C = 50 μm. (F) Electron micrograph depicting the intimate enwrapping of pre- and postsynaptic terminals by astroglial processes (BG: Bergmann glial processes, scale bar: 1 μm). (G) Knock-in of CreERT2 into the GLAST locus leads to tamoxifen-sensitive recombination in all astrocytes with endogenous GLAST promoter activity (Mori et al., 2006). The DNA recombinase variant CreERT2 is trapped in the cytosol by heat shock proteins (HSP), after tamoxifen application the protein is released and translocated into the nucleus. (H,I) Transgenic GFAP-CreERT2 mice generated by non-homologous recombination can also be used to target astrocytes (Hirrlinger et al., 2006). The Cre/loxP system can either be used to selective excise gene alleles of interest (G,H; knockout) or to express genes of interest (e.g., reporter proteins such as GFP or genetically encoded Ca2+ indicators), but also to restore gene function (I) (Lioy et al., 2011). (J) Alternatively, the binary tTA/tetO system composed of (1) promoter-controlled expression of a tetracyclin transactivator protein; and (2) tetracycline/doxycycline-responsive elements driving the expression of proteins-of-interest (Pascual et al., 2005). This system allows for a certain degree of reversible gene regulation.
Mentions: Astrocytes represent an abundant, but also heterogeneous group of glial cells in all regions of the brain (Figures 1A–F). Their numerous interactions with capillaries and neurons are important signaling pathways for physiological brain function. Astrocytes actively control signal processing and transmission at the tripartite synapse (Perea et al., 2009). Originally, astrocytes were regarded as silent non-excitable cells, since they do not communicate via electrical signals. But now, it has become very clear that astroglial signaling is encoded in complex spatial and temporal patterns of Ca2+ changes within subcellular compartments as well as throughout cellular networks coupled by gap junctions. Intracellular Ca2+ rises indicate how they sense activity of their surroundings (Zorec et al., 2012; Araque et al., 2014; Verkhratsky and Parpura, 2014). Intracellular changes of another cation, Na+, have been recognized as an additional or alternative indicator of astrocyte activation (Kirischuk et al., 2012; Verkhratsky et al., 2013; Rose and Chatton, 2015). Even over longer distances astrocytes can convey various signals, e.g., inositol-1,4,5-trisphosphate (IP3) or cyclic nucleotides that pass through gap junctions and functionally couple the astroglial syncytium (Giaume and Liu, 2012; Theis and Giaume, 2012). Within these networks information spreads with tens of μm/s speed, still several orders of magnitude slower than the propagation of neuronal action potentials (Haydon and Nedergaard, 2015). The interactions of astrocytes with neurons are largely based on astroglial receptors that sense neuronal communication or on the release of gliotransmitters acting back on synaptic transmission. The general importance of astrocytes for brain function is uncovered by the devastating point mutations in single genes encoding transcription factors since these factors can control extended sets of gene programs. Genetically modified mice addressing astrocyte function have been instrumental in uncovering their role in the living animal.

Bottom Line: Furthermore, such genetic approaches have also been used to restore astrocyte function.In these studies two alternatives were employed to achieve proper genetic targeting of astrocytes: transgenes using the promoter of the human glial fibrillary acidic protein (GFAP) or homologous recombination into the glutamate-aspartate transporter (GLAST) locus.We will highlight their specific properties that could be relevant for their use.

View Article: PubMed Central - PubMed

Affiliation: Molecular Physiology, Center for Integrative Physiology and Molecular Medicine (CIPMM), University of Saarland Homburg, Germany.

ABSTRACT
During the last two decades numerous genetic approaches affecting cell function in vivo have been developed. Current state-of-the-art technology permits the selective switching of gene function in distinct cell populations within the complex organization of a given tissue parenchyma. The tamoxifen-inducible Cre/loxP gene recombination and the doxycycline-dependent modulation of gene expression are probably the most popular genetic paradigms. Here, we will review applications of these two strategies while focusing on the interactions of astrocytes and neurons in the central nervous system (CNS) and their impact for the whole organism. Abolishing glial sensing of neuronal activity by selective deletion of glial transmitter receptors demonstrated the impact of astrocytes for higher cognitive functions such as learning and memory, or the more basic body control of muscle coordination. Interestingly, also interfering with glial output, i.e., the release of gliotransmitters can drastically change animal's physiology like sleeping behavior. Furthermore, such genetic approaches have also been used to restore astrocyte function. In these studies two alternatives were employed to achieve proper genetic targeting of astrocytes: transgenes using the promoter of the human glial fibrillary acidic protein (GFAP) or homologous recombination into the glutamate-aspartate transporter (GLAST) locus. We will highlight their specific properties that could be relevant for their use.

No MeSH data available.


Related in: MedlinePlus