Developmental changes in β-subunit composition of Na,K-ATPase in the Drosophila eye

Ion homeostasis is a fundamental cellular process particularly important in excitable cell activities such as hearing. It relies on the Na + /K + ATPase (also referred to as the Na pump), which is composed of a catalytic α subunit and a β subunit required for its transport to the plasma membrane and for regulating its activity. We show that α and β subunits are expressed in Johnston's organ (JO), the Drosophila auditory organ. We knocked down expression of α subunits (ATPα and α-like) and β subunits (nrv1, nrv2, and nrv3) individually in JO with UAS/Gal4-mediated RNAi. U sing the energy of ATP hydrolysis, the Na pump extrudes cytoplasmic Na + (out) and extracellular K + (in) in a 3:2 ratio and maintains the gradient of these cations across the membrane (1, 2), thus controlling the electrolytic and fluid balance in the cells and organs throughout the body (1). Among its other functions, the Na pump helps maintain the resting potential of cells, regulates cellular volume, and facilitates transport of solutes in and out of cells. Ion homeostasis of most biological systems depends on the Na pump. In the auditory system, this pump has been linked to the maintenance of the inner ear osmotic balance (3). The scala media of the inner ear is filled with a K + -rich extracellular fluid known as endolymph, which is essential for preserving the sensory structures and supporting transduction. Maintaining the endolymph homeostasis is critical to sustain auditory functions. Loss of endolymphatic balance causes collapse of the endolymphatic compartment, leading to hearing loss in mammals (4). K + channels and pumps, including the Na pump, ensure proper cycling and secretion of K + ions in the stria vascularis cells of the cochlea. The Na pump has also been linked to age-related hearing loss (5) and Ménière disease (6). A detailed functional analysis of this pump is therefore necessary to gain insight into the molecular physiology of hearing loss resulting from loss of auditory ionic homeostasis.Although vertebrate and invertebrate auditory systems differ structurally, they evolved from the same primitive mechanosensors (7,8), and there are striking developmental genetic similarities between the two lineages. The fly auditory organ, Johnston's organ (JO), is a chordotonal organ (cho) housed in the second antennal segment (9). The JO comprises an array of ∼250 auditory units or scolopidia. Each scolopidium comprises two to three ciliated sensory neurons associated with several support cells. These bipolar neurons are monodendritic with a single distal cilium and a proximal axon (Fig. 1A). The scolopale cell, a principal support cell, encloses the neuronal dendrites in a fluid-filled lumen, the scolopale space. This fluid, the receptor lymph, resembles cochlear endolymph and, like the endolymph, is believed to be rich in K + ions (7). The scolopale cells are structurally enforced with actin-based scolopale rods. Auditory mechanosensation involves the transduction of the mechanical sound stimulus (10) through the rotation of distal...

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“…In adult flies, ATPα is expressed in the eye and brain (Fig. S1A), consistent with other studies (19), and in JO (Fig. 1B).…”

Section: Resultssupporting

confidence: 79%

“…S7). Previously, Nrv1 protein was found to express at low levels in the R7-R8 adult photoreceptor cells, but to be absent in brain tissue (19). From the differential staining pattern of Nrv5F7 and Nrv3 (Fig.…”

Section: Resultsmentioning

confidence: 99%

Cell-type–specific roles of Na ⁺ /K ⁺ ATPase subunits in Drosophila auditory mechanosensation

Roy

Sivan-Loukianova

Eberl

2012

Proc. Natl. Acad. Sci. U.S.A.

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“…Conversely, BgNrv2 is preferentially expressed in nervous tissues and its presence in the ovary is very low when compared with BgNrv1 levels.This generalized expression in B. germanica is similar to that observed in D. melanogaster, where Nrv1 is broadly distributed throughout the fly but is not detected in head (Sun et al, 1998), whereas Nrv2 is the most abundant with a specific nervous system distribution (Sun and Salvaterra, 1995a, b;Sun et al, 1998). Both proteins have an overlapping yet distinctive distribution with Nrv3, which is enriched in the eye (Baumann et al, 2010). A number of mammalian species also contain multiple forms of β-subunits that are expressed in characteristic cell-and tissue type-specific patterns related to the different roles described for each isoform (Blanco and Mercer, 1998;Grindstaff et al, 1996;Shyjan et al, 1990a;Shyjan et al, 1990b;Shyjan and Levenson, 1989;Watts et al, 1991).…”

Section: Discussionsupporting

confidence: 53%

“…Moreover, Sun and Salvaterra (1995a) purified and characterized a nervous system-specific glycoprotein antigen from adult D. melanogaster heads corresponding to a β-subunit of a Na + , K + -ATPase, and named it Nervana (nerve antigen; Nrv). These authors subsequently described the expression, localization and function of three Nervana isoforms in the nervous system of D. melanogaster embryos (Baumann et al, 2010;Sun and Salvaterra, 1995a, b;Sun et al, 1998;Xu et al, 1999). More recently, new functions have been described for these β-subunits related to cell-cell contact (Genova and Fehon, 2003;Kometiani et al, 1998;Paul et al, 2007;Vagin et al, 2006), signal transduction (Kometiani et al, 1998) and epithelial polarity in the embryo (Laprise et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

RNAi reveals the key role of Nervana 1 in cockroach oogenesis and embryo development

Irles¹,

Silva-Torres²,

Piulachs³

2013

Insect Biochemistry and Molecular Biology

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Na+ , K + -ATPases is a heterodimer protein consisting of α-and β-subunits that control the ion transport through cell membranes . In insects the β-subunit of the Na + , K + -ATPase, known as Nervana, was characterized as a nervous system-specific glycoprotein antigen from adult Drosophila melanogaster heads. Nervana is expressed ubiquitously in all insect tissues, and in epithelial cells appeared located in a basolateral position as part of the septate junctions. Herein we study two Nervana isoforms fromBlattella germanica, a cockroach species with panoistic ovaries. The sequencing and the phylogenetic analysis results suggest that these two isoforms are orthologs of D.melanogaster Nervana 1 and Nervana 2, respectively. Nervana 1 is highly expressed in the ovary of B. germanica, and depleting its expression results in changes in oocyte shape that do not impair oviposition. However, the resulting embryos show different defects and never hatch. These findings highlight the importance of this type of membrane pump in insect oogenesis as well as in embryo development, and its possible regulation by juvenile hormone.

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“…The Drosophila visual system expresses only one type of α subunit, ATPα, and three β subunits, Nrv1-3 (Ashmore et al, 2009; Baumann et al, 2010; Okamura et al, 2003; Palladino et al, 2003; Takeyasu et al, 2001). In this study, we used Drosophila photoreceptors as a genetic model to study the cell-autonomous functions of neuronal Na + /K + -ATPase.…”

Section: Introductionmentioning

confidence: 99%

Loss of Na+/K+-ATPase in Drosophila photoreceptors leads to blindness and age-dependent neurodegeneration

Zhuo

Reddig

2014

Experimental Neurology

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The activity of Na+/K+-ATPase establishes transmembrane ion gradients and is essential to cell function and survival. Either dysregulation or deficiency of neuronal Na+/K+-ATPase has been implicated in the pathogenesis of many neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease and rapid-onset dystonia Parkinsonism. However, genetic evidence that directly links neuronal Na+/K+-ATPase deficiency to in vivo neurodegeneration has been lacking. In this study, we use Drosophila photoreceptors to investigate the cell-autonomous effects of neuronal Na+/K+ ATPase. Loss of ATPα, an α subunit of Na+/K+-ATPase, in photoreceptors through UAS/Gal4-mediated RNAi eliminated the light-triggered depolarization of the photoreceptors, rendering the fly virtually blind in behavioral assays. Intracellular recordings indicated that ATPα knockdown photoreceptors were already depolarized in the dark, which was due to a loss of intracellular K+. Importantly, ATPα knockdown resulted in the degeneration of photoreceptors in older flies. This degeneration was independent of light and showed characteristics of apoptotic/hybrid cell death as observed via electron microscopy analysis. Loss of Nrv3, a Na+/K+-ATPase β subunit, partially reproduced the signaling and degenerative defects observed in ATPα knockdown flies. Thus, loss of Na+/K+-ATPase not only eradicates visual function but also causes age-dependent degeneration in photoreceptors, confirming the link between neuronal Na+/K+ ATPase deficiency and in vivo neurodegeneration. This work also establishes Drosophila photoreceptors as a genetic model for studying the cell-autonomous mechanisms underlying neuronal Na+/K+ ATPase deficiency-mediated neurodegeneration.

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Developmental changes in β-subunit composition of Na,K-ATPase in the Drosophila eye

Cited by 13 publications

References 45 publications

Cell-type–specific roles of Na ⁺ /K ⁺ ATPase subunits in Drosophila auditory mechanosensation

Cell-type–specific roles of Na ⁺ /K ⁺ ATPase subunits in Drosophila auditory mechanosensation

RNAi reveals the key role of Nervana 1 in cockroach oogenesis and embryo development

Loss of Na+/K+-ATPase in Drosophila photoreceptors leads to blindness and age-dependent neurodegeneration

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Developmental changes in β-subunit composition of Na,K-ATPase in the Drosophila eye

Cited by 13 publications

References 45 publications

Cell-type–specific roles of Na + /K + ATPase subunits in Drosophila auditory mechanosensation

Cell-type–specific roles of Na + /K + ATPase subunits in Drosophila auditory mechanosensation

RNAi reveals the key role of Nervana 1 in cockroach oogenesis and embryo development

Loss of Na+/K+-ATPase in Drosophila photoreceptors leads to blindness and age-dependent neurodegeneration

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Cell-type–specific roles of Na ⁺ /K ⁺ ATPase subunits in Drosophila auditory mechanosensation

Cell-type–specific roles of Na ⁺ /K ⁺ ATPase subunits in Drosophila auditory mechanosensation