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Glia-related circadian plasticity in the visual system of Diptera.

Górska-Andrzejak J - Front Physiol (2013)

Bottom Line: It is observed in terminals of the compound eye photoreceptor cells, the peripheral oscillators expressing the clock genes.However, it has been found also in their postsynaptic partners, the L1 and L2 monopolar cells, in which the activity of the clock genes have not yet been detected.This paper summarizes the morphological and biochemical rhythms in glia of the optic lobe, shows how they contribute to circadian plasticity, and discusses how glial clocks may modulate circadian rhythms in the lamina.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology and Imaging, Institute of Zoology, Jagiellonian University Kraków, Poland.

ABSTRACT
The circadian changes in morphology of the first visual neuropil or lamina of Diptera represent an example of the neuronal plasticity controlled by the circadian clock (circadian plasticity). It is observed in terminals of the compound eye photoreceptor cells, the peripheral oscillators expressing the clock genes. However, it has been found also in their postsynaptic partners, the L1 and L2 monopolar cells, in which the activity of the clock genes have not yet been detected. The circadian input that the L1 and L2 receive seems to originate not only from the retina photoreceptors and from the circadian pacemaker neurons located in the brain, but also from the glial cells that express the clock genes and thus contain circadian oscillators. This paper summarizes the morphological and biochemical rhythms in glia of the optic lobe, shows how they contribute to circadian plasticity, and discusses how glial clocks may modulate circadian rhythms in the lamina.

No MeSH data available.


The visual system of the fruit fly, Drosophila melanogaster. (A) Scanning electron micrograph of a head and a large compound eye. The eye is composed of approximately 800 hexagonal units called facets or ommatidia (arrow). The ommatidial array of photoreceptors in the retina receives photic and visual information, transduces it into receptor action potentials and transmits to underlying optic lobe. Scale bar: 200 μm. (B) Confocal image of the optic lobe of transgenic flies Repo-Gal4 × UAS-S65T-GFP, in horizontal section. Targeted expression of Green Fluorescence Protein (GFP) to glial cells reveals the general morphology of the optic lobe. There are three synaptic regions (neuropils) beneath the retina of the compound eye: the lamina (L), the medulla (M), and the lobula that in Diptera consists of the lobula (Lo) and the lobula plate (Lp). Lc, lamina cortex; Ln, lamina neuropil; Mc, medulla cortex; Mn, medulla neuropil; ch, chiasm. Scale bar: 20 μm. (C) Schematic representation of so far identified types of glia (based on Edwards et al., 2012) revealing their general morphology and relative locations in the optic lobe: fg, fenestrated glia; psdg, pseudocartridge glia; dsg, distal satellite glia; psg, proximal satellite glia; eg, epithelial glia; mg, marginal glia; mcg, medulla cortex glia; aslg, astrocyte-like glia of the distal medulla neuropil; ng, another type of the distal medulla neuropil glia; spg, serpentine glia; chg, chandelier glia; ocg, outer chiasm glia (giant and small ocg); icg, inner chiasm glia; lcg, lobula cortex glia; M7, the serpentine layer. Certain types of glia (eg, aslg, and/or ng, mcg, lcg, ocg, icg) can be also discern in the tissue visible in the background being marked by GFP. Scale bar: 20 μm.
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Figure 1: The visual system of the fruit fly, Drosophila melanogaster. (A) Scanning electron micrograph of a head and a large compound eye. The eye is composed of approximately 800 hexagonal units called facets or ommatidia (arrow). The ommatidial array of photoreceptors in the retina receives photic and visual information, transduces it into receptor action potentials and transmits to underlying optic lobe. Scale bar: 200 μm. (B) Confocal image of the optic lobe of transgenic flies Repo-Gal4 × UAS-S65T-GFP, in horizontal section. Targeted expression of Green Fluorescence Protein (GFP) to glial cells reveals the general morphology of the optic lobe. There are three synaptic regions (neuropils) beneath the retina of the compound eye: the lamina (L), the medulla (M), and the lobula that in Diptera consists of the lobula (Lo) and the lobula plate (Lp). Lc, lamina cortex; Ln, lamina neuropil; Mc, medulla cortex; Mn, medulla neuropil; ch, chiasm. Scale bar: 20 μm. (C) Schematic representation of so far identified types of glia (based on Edwards et al., 2012) revealing their general morphology and relative locations in the optic lobe: fg, fenestrated glia; psdg, pseudocartridge glia; dsg, distal satellite glia; psg, proximal satellite glia; eg, epithelial glia; mg, marginal glia; mcg, medulla cortex glia; aslg, astrocyte-like glia of the distal medulla neuropil; ng, another type of the distal medulla neuropil glia; spg, serpentine glia; chg, chandelier glia; ocg, outer chiasm glia (giant and small ocg); icg, inner chiasm glia; lcg, lobula cortex glia; M7, the serpentine layer. Certain types of glia (eg, aslg, and/or ng, mcg, lcg, ocg, icg) can be also discern in the tissue visible in the background being marked by GFP. Scale bar: 20 μm.

Mentions: Studies on the housefly, Musca domestica and the fruit fly, Drosophila melanogaster have shown that in the visual system of Diptera (Figure 1), the circadian plasticity manifests itself both in the retina of the large compound eye (Figure 1A) (Chen et al., 1992) and in the first visual neuropil beneath the compound eye, the lamina (Figure 1B) (Pyza and Górska-Andrzejak, 2008; Pyza, 2010). In the retina, the circadian clock regulates the process of phototransduction, the sensitivity of photoreceptors to light, and their adaptation to changing light conditions (Giebultowicz, 2000; Pyza, 2010). In the underlying lamina, the circadian control is even more pronounced (Pyza and Meinertzhagen, 1997). In the so called cartridges—the synaptic units of lamina neuropil (Figure 2)—both the terminals of photoreceptors (R1–R6) and the axons of their most conspicuous postsynaptic partners (the L1 and L2 interneurons, cf. Figure 2A) exhibit robust structural rhythms (Pyza and Meinertzhagen, 1995, 1997, 1999; Górska-Andrzejak et al., 2005; Barth et al., 2010). It has been shown that in the fruit fly the volume of photoreceptor terminals changes in a circadian manner (Barth et al., 2010), whereas in the housefly the endogenous reorganization of organelles within R1–R6 terminals is maintained under circadian modulation (Pyza and Meinertzhagen, 1997). In Musca, the number of screening pigment granules and the number of inter-receptor invaginations from neighboring terminals show circadian changes (Pyza and Meinertzhagen, 1997). The number of synaptic contacts between R1 and R6 terminals and axons of L1, L2 monopolar cells (the tetrad synapses) also undergoes certain changes over the course of 24 h, but this modulation was found to be rather weak and not of circadian origin (Pyza and Meinertzhagen, 1993). In case of Drosophila, changes in the number of tetrad presynaptic ribbons have been reported as circadian by Barth et al. (2010). Nevertheless, additional studies that could provide more quantitative insight into the origin of tetrads daily fluctuations would be helpful in clarifying this issue.


Glia-related circadian plasticity in the visual system of Diptera.

Górska-Andrzejak J - Front Physiol (2013)

The visual system of the fruit fly, Drosophila melanogaster. (A) Scanning electron micrograph of a head and a large compound eye. The eye is composed of approximately 800 hexagonal units called facets or ommatidia (arrow). The ommatidial array of photoreceptors in the retina receives photic and visual information, transduces it into receptor action potentials and transmits to underlying optic lobe. Scale bar: 200 μm. (B) Confocal image of the optic lobe of transgenic flies Repo-Gal4 × UAS-S65T-GFP, in horizontal section. Targeted expression of Green Fluorescence Protein (GFP) to glial cells reveals the general morphology of the optic lobe. There are three synaptic regions (neuropils) beneath the retina of the compound eye: the lamina (L), the medulla (M), and the lobula that in Diptera consists of the lobula (Lo) and the lobula plate (Lp). Lc, lamina cortex; Ln, lamina neuropil; Mc, medulla cortex; Mn, medulla neuropil; ch, chiasm. Scale bar: 20 μm. (C) Schematic representation of so far identified types of glia (based on Edwards et al., 2012) revealing their general morphology and relative locations in the optic lobe: fg, fenestrated glia; psdg, pseudocartridge glia; dsg, distal satellite glia; psg, proximal satellite glia; eg, epithelial glia; mg, marginal glia; mcg, medulla cortex glia; aslg, astrocyte-like glia of the distal medulla neuropil; ng, another type of the distal medulla neuropil glia; spg, serpentine glia; chg, chandelier glia; ocg, outer chiasm glia (giant and small ocg); icg, inner chiasm glia; lcg, lobula cortex glia; M7, the serpentine layer. Certain types of glia (eg, aslg, and/or ng, mcg, lcg, ocg, icg) can be also discern in the tissue visible in the background being marked by GFP. Scale bar: 20 μm.
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Related In: Results  -  Collection

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Figure 1: The visual system of the fruit fly, Drosophila melanogaster. (A) Scanning electron micrograph of a head and a large compound eye. The eye is composed of approximately 800 hexagonal units called facets or ommatidia (arrow). The ommatidial array of photoreceptors in the retina receives photic and visual information, transduces it into receptor action potentials and transmits to underlying optic lobe. Scale bar: 200 μm. (B) Confocal image of the optic lobe of transgenic flies Repo-Gal4 × UAS-S65T-GFP, in horizontal section. Targeted expression of Green Fluorescence Protein (GFP) to glial cells reveals the general morphology of the optic lobe. There are three synaptic regions (neuropils) beneath the retina of the compound eye: the lamina (L), the medulla (M), and the lobula that in Diptera consists of the lobula (Lo) and the lobula plate (Lp). Lc, lamina cortex; Ln, lamina neuropil; Mc, medulla cortex; Mn, medulla neuropil; ch, chiasm. Scale bar: 20 μm. (C) Schematic representation of so far identified types of glia (based on Edwards et al., 2012) revealing their general morphology and relative locations in the optic lobe: fg, fenestrated glia; psdg, pseudocartridge glia; dsg, distal satellite glia; psg, proximal satellite glia; eg, epithelial glia; mg, marginal glia; mcg, medulla cortex glia; aslg, astrocyte-like glia of the distal medulla neuropil; ng, another type of the distal medulla neuropil glia; spg, serpentine glia; chg, chandelier glia; ocg, outer chiasm glia (giant and small ocg); icg, inner chiasm glia; lcg, lobula cortex glia; M7, the serpentine layer. Certain types of glia (eg, aslg, and/or ng, mcg, lcg, ocg, icg) can be also discern in the tissue visible in the background being marked by GFP. Scale bar: 20 μm.
Mentions: Studies on the housefly, Musca domestica and the fruit fly, Drosophila melanogaster have shown that in the visual system of Diptera (Figure 1), the circadian plasticity manifests itself both in the retina of the large compound eye (Figure 1A) (Chen et al., 1992) and in the first visual neuropil beneath the compound eye, the lamina (Figure 1B) (Pyza and Górska-Andrzejak, 2008; Pyza, 2010). In the retina, the circadian clock regulates the process of phototransduction, the sensitivity of photoreceptors to light, and their adaptation to changing light conditions (Giebultowicz, 2000; Pyza, 2010). In the underlying lamina, the circadian control is even more pronounced (Pyza and Meinertzhagen, 1997). In the so called cartridges—the synaptic units of lamina neuropil (Figure 2)—both the terminals of photoreceptors (R1–R6) and the axons of their most conspicuous postsynaptic partners (the L1 and L2 interneurons, cf. Figure 2A) exhibit robust structural rhythms (Pyza and Meinertzhagen, 1995, 1997, 1999; Górska-Andrzejak et al., 2005; Barth et al., 2010). It has been shown that in the fruit fly the volume of photoreceptor terminals changes in a circadian manner (Barth et al., 2010), whereas in the housefly the endogenous reorganization of organelles within R1–R6 terminals is maintained under circadian modulation (Pyza and Meinertzhagen, 1997). In Musca, the number of screening pigment granules and the number of inter-receptor invaginations from neighboring terminals show circadian changes (Pyza and Meinertzhagen, 1997). The number of synaptic contacts between R1 and R6 terminals and axons of L1, L2 monopolar cells (the tetrad synapses) also undergoes certain changes over the course of 24 h, but this modulation was found to be rather weak and not of circadian origin (Pyza and Meinertzhagen, 1993). In case of Drosophila, changes in the number of tetrad presynaptic ribbons have been reported as circadian by Barth et al. (2010). Nevertheless, additional studies that could provide more quantitative insight into the origin of tetrads daily fluctuations would be helpful in clarifying this issue.

Bottom Line: It is observed in terminals of the compound eye photoreceptor cells, the peripheral oscillators expressing the clock genes.However, it has been found also in their postsynaptic partners, the L1 and L2 monopolar cells, in which the activity of the clock genes have not yet been detected.This paper summarizes the morphological and biochemical rhythms in glia of the optic lobe, shows how they contribute to circadian plasticity, and discusses how glial clocks may modulate circadian rhythms in the lamina.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology and Imaging, Institute of Zoology, Jagiellonian University Kraków, Poland.

ABSTRACT
The circadian changes in morphology of the first visual neuropil or lamina of Diptera represent an example of the neuronal plasticity controlled by the circadian clock (circadian plasticity). It is observed in terminals of the compound eye photoreceptor cells, the peripheral oscillators expressing the clock genes. However, it has been found also in their postsynaptic partners, the L1 and L2 monopolar cells, in which the activity of the clock genes have not yet been detected. The circadian input that the L1 and L2 receive seems to originate not only from the retina photoreceptors and from the circadian pacemaker neurons located in the brain, but also from the glial cells that express the clock genes and thus contain circadian oscillators. This paper summarizes the morphological and biochemical rhythms in glia of the optic lobe, shows how they contribute to circadian plasticity, and discusses how glial clocks may modulate circadian rhythms in the lamina.

No MeSH data available.