Disease relevance of Slc12a5

• We demonstrate that animals deficient in KCC2 exhibit frequent generalized seizures and die shortly after birth [1].
• To produce various types of gene-targeting constructions rapidly and with minimum effort, we developed a strategy, that utilizes a highly efficient in vitro transposition reaction of phage Mu, and tested it in a targeting of the mouse Kcc2 gene locus [2].
• KCC2 was expressed wherever E(Cl) is either known or predicted to be negative to E(rest) (ganglion cells, bipolar axons, and OFF bipolar dendrites), whereas NKCC was expressed wherever E(Cl) is either known or predicted to be positive to E(rest) (horizontal cells and ON bipolar dendrites) [3].

High impact information on Slc12a5

• This loss of GABAergic and glycinergic synaptic transmission does not impair the development of inhibitory synapses or the expression of KCC2, the K+ -Cl- cotransporter known to be essential for the establishment of inhibitory neurotransmission [4].
• By expression studies in Xenopus oocytes, we show that kinase-active WNK3 increases Cl(-) influx via NKCC1, and that it inhibits Cl(-) exit through KCC1 and KCC2; kinase-inactive WNK3 has the opposite effects [5].
• BDNF regulates spontaneous correlated activity at early developmental stages by increasing synaptogenesis and expression of the K+/Cl- co-transporter KCC2 [6].
• By combining the information from overlapping minicontigs, the sequence of the entire 10,288-bp region of mouse genome including six exons of mouse Kcc2 gene was obtained [7].
• Membrane proteins that typically extrude chloride (KCC-2 cotransporter, CLC-2 channel) were absent from the GT1-7 immortalized GnRH cell line and GnRH neurons in situ or were not localized to the proper cell compartment for function [8].

Biological context of Slc12a5

• In transgenic mice, however, KCC2 reporters with or without deletion of the NRSE(KCC2) were expressed exclusively in neurones and predominantly in the CNS with a similar pattern and developmental up-regulation as endogenous KCC2 [9].
• Overexpression of neurone-restrictive silencer factor repressed the reporter activity in vitro, apparently via a neurone restrictive silencer element (NRSE(KCC2)) within intron 1 of the mouse KCC2 gene [9].
• Moreover, a third transgene with just a 1.4-kb KCC2 promoter region lacking the NRSE(KCC2)-bearing intron 1 was still expressed predominantly in neural tissues [9].
• Here, we show that the KCC2 gene (alias SLC12a5) has multiple transcription start sites and characterize the activity of 6.8 kb of mouse KCC2 gene regulatory sequence (spanning 1.4 kb upstream from exon 1 to exon 2) using luciferase reporters [9].
• Behavioural phenotypes of hypomorphic KCC2-deficient mice [10].

Anatomical context of Slc12a5

• By contrast, KCC2 was localized to nearly all vasopressin neurons of the supraoptic nucleus [11].
• KCC2 expression paralleled neuronal differentiation and preceded the decline of the GABA reversal potential (EGABA) in spinal cord motoneurons and hippocampal pyramidal cells [12].
• Based on these results, we propose a model for functional coupling between the Na+, K+-ATPase alpha2 subunit and KCC2, which excludes Cl- from the cytosol in respiratory center neurons [13].
• The alpha2 subunit and a neuron-specific K-Cl cotransporter KCC2 were coimmunoprecipitated in a purified synaptic membrane fraction of wild-type fetuses [13].
• Unlike KCC2, NCBE is expressed in the peripheral nervous system and in non-neuronal tissues as the choroid plexus, the dura, and some epithelia including the acid secreting epithelium of the stomach and the duodenal epithelium [14].

Associations of Slc12a5 with chemical compounds

• Interestingly, whereas BDNF does not alter the expression of GABA and glutamate ionotropic receptors, it does raise the expression of the recently cloned K(+)/Cl(-) KCC2 co-transporter, which is responsible for the conversion of GABA responses from depolarizing to inhibitory, through the control of the Cl(-) potential [6].
• The K+/Cl- co-transporter KCC2 maintains the low intracellular chloride concentration required for fast synaptic inhibition and is exclusively expressed in neurones of the CNS [9].
• Heterogeneous expression of the potassium-chloride cotransporter KCC2 in gonadotropin-releasing hormone neurons of the adult mouse [11].
• KCC2, is exclusively expressed in neurons where it is thought to drive intracellular Cl- to low concentrations and shift the reversal potential for Cl- conductances such as GABA(A) or glycine receptor channels, thus participating in the postnatal development of inhibitory mechanisms in the brain [1].
• KCC2 activity is thought to depend on phosphorylation by endogenous tyrosine kinases [12].

Regulatory relationships of Slc12a5

• Indeed, NCBE is expressed very early in CNS neurons and precedes the expression of KCC2 [14].
• A recent in vitro study [Ganguly et al. (2001) Cell, 105, 521-532] showed that KCC2 expression may be under the trophic control of GABAA receptor-mediated transmission [15].

Other interactions of Slc12a5

• As NCBE, a sodium-dependent chloride-bicarbonate exchanger, also lowers [Cl(-)](i) and may thus modulate the GABA-response, we analyzed its expression during prenatal mouse development before establishment of the mature KCC2 expression [14].
• Blockade of GABAA-mediated transmission with picrotoxin did not affect the expression levels of KCC2 protein either [15].

Analytical, diagnostic and therapeutic context of Slc12a5

• We assigned human SLC12A5 to 20q12-->q13.1 and its murine homolog, Slc12a5, to 5G2-G3 by fluorescence in situ hybridization (FISH) [16].
• Here, we analyzed the expression pattern of KCC2 during murine embryonic and postnatal development by in situ hybridization and Western blot analysis [12].
• Western blots confirmed a constant level of KCC2 in the brainstem, and immunohistochemistry showed that the protein is diffusely distributed within neonatal LSO neurons, becoming integrated into the plasma membrane only with increasing age [17].

References