Scn7a

Sodium channel protein type 7 subunit alpha (Nax channel) (Sodium channel Nav2.3)

Spatial tier: RESTRICTED · Class: ION_CHANNEL · Top region: ME (Median eminence) · Positive regions: 23/554

43.9Discovery Score

41.5Targetability Score

CEvidence grade C

What this means: Scn7a: fine CCF profile is restricted toward ME (top regions: ME, OV, AD, VISpor4, NLOT2; 23 positive regions); direct spatial validation is still required.

Function in ME: evidence, prediction, innovation

Gene function

SCN7A encodes Nax (Nav2.3), an atypical member of the voltage-gated sodium channel family that has lost voltage sensing. Instead it behaves as a concentration-gated sodium leak channel that opens when extracellular sodium rises above roughly 150 mM. It is expressed in glia rather than neurons, is functionally coupled to the Na+/K+-ATPase and to lactate signalling, and constitutes the brain's sensor for body-fluid sodium, initiating salt aversion and sympathetic pressor responses.

Region function

The median eminence is the neurohaemal circumventricular interface at the base of the hypothalamus, where tanycytes and fenestrated portal capillaries let hypophysiotropic peptides such as GnRH, TRH, CRH, GHRH and dopamine reach the anterior pituitary.

Published in this region

inferred No region-specific literature found. Watanabe et al. 2006 localised Nax to the glial lamellate processes of the sensory circumventricular organs - subfornical organ and OVLT - and to ependymal cells, the same specialised glial class as median-eminence tanycytes; Nomura et al. 2019 showed that central Nax sensing of rising sodium drives sympathetically mediated blood-pressure elevation, and Sakuta et al. 2020 showed Nax-positive OVLT glia release epoxyeicosatrienoic acids, but none of this work examined the median eminence.

Predicted function

Prediction: Nax in median-eminence tanycytes is predicted to act as the sodium sensor of the neuroendocrine interface, translating rises in portal and cerebrospinal-fluid sodium into tanycyte lactate release and altered barrier permeability, and thereby coupling salt and dehydration status to the output of GnRH, TRH and CRH terminals. Tanycyte-restricted Scn7a deletion using Rax-CreERT2 is predicted to leave sodium appetite partly intact (since the sensory circumventricular organs still function) but to abolish the dehydration-induced remodelling of tanycyte endfeet and blunt the suppression of the reproductive axis and the rise in vasopressin that follow salt loading.

Innovation

★★★★☆ 4/5 Nax sodium sensing is established in neighbouring circumventricular organs but never tested in the median eminence, where tanycyte Cre lines now make the experiment straightforward.

Tools

Scn7a/Nax knockout mice and the Nax-lacZ knock-in reporter (Noda lab); anti-Nax antibodies; no selective pharmacology, so genetics is required; Rax-CreERT2 and Gfap-CreER for tanycytes and astroglia; hypertonic saline loading and sodium-appetite assays as the physiological challenge.

References

Direct evidence located at the region

Scn7a Allen ISH at the CCF centroid of ME

Allen ISH experiment 71325432, section image 71206891 (section 144): the section that contains the CCF centroid of Median eminence according to the Allen image-to-atlas alignment (reference_to_image), with a 2 mm window around that point. Left: whole section, red box = window. Middle: ISH signal. Right: Allen's expression-mask view of the same window. open this image in the Allen viewer

Look it up yourself: Allen Mouse Brain ISH for Scn7a Allen reference atlas: ME (structure 10671)ABC Atlas MERFISH viewer(in the ABC Atlas choose dataset MERFISH-C57BL6J-638850-CCF, colour cells by gene "Scn7a" or by parcellation_substructure "ME")All genes confined to ME + 3-D brain

Direct spatial evidence

ME MERFISH region locator — Real single-cell MERFISH coordinates for the ME (Median eminence) section -- our own ground-truth data, showing exactly where this region sits, independent of whether the Allen ISH section below is easy to read.

Regional expression figure

Predicted WMB × fine-CCF profile; not direct full-transcriptome spatial measurement.

Spatial profile

4.11

3.25

2.33

VISpor4

2.06

NLOT2

1.79

TEa4

1.74

PL2/3

1.54

VISC4

1.52

VISli4

1.49

AUDv4

1.44

AUDpo4

1.44

NLOT3

1.38

VISpl4

1.31

IPA

1.25

IAD

1.24

PVpo

1.23

ARH

1.2

GU4

1.18

PVi

1.16

Evidence and specificity

Evidence status: PREDICTED_FINE
Direct sources: None; predicted localization only
Exclusive threshold: 12 positive regions out of 554
Spatial specificity: 0.301
Top-region fraction: 0.065
Filter status: PASS

Interpretation limits

Cell-type-to-region projection is imputed expression, not direct spatial measurement.
Adult reference atlases do not establish stability across age, sex, strain, state, or disease.
Transcript abundance does not guarantee protein abundance or genetic-tool performance.