Phenotypic Mutation 'jitter' (pdf version)
Allelejitter
Mutation Type synonymous
Chromosome18
Coordinate45,694,320 bp (GRCm39)
Base Change T ⇒ C (forward strand)
Gene Kcnn2
Gene Name potassium intermediate/small conductance calcium-activated channel, subfamily N, member 2
Synonym(s) small conductance calcium-activated potassium channel 2, bc, fri, SK2
Chromosomal Location 45,401,927-45,819,091 bp (+) (GRCm39)
MGI Phenotype PHENOTYPE: Mice homozygous for a point mutation exhibit tremor and gait abnormalities. Homozygous null mice lack the apamin sensitive component of the medium afterhyperpolarization current but have normal hippocampal morphology. [provided by MGI curators]
Accession Number

NCBI RefSeq: NM­_080465; MGI: 2153182

MappedYes 
Amino Acid Change
Institutional SourceBeutler Lab
Gene Model not available
AlphaFold P58390
SMART Domains Protein: ENSMUSP00000067884
Gene: ENSMUSG00000054477

DomainStartEndE-ValueType
low complexity region 62 76 N/A INTRINSIC
low complexity region 84 90 N/A INTRINSIC
low complexity region 98 114 N/A INTRINSIC
low complexity region 129 141 N/A INTRINSIC
low complexity region 158 180 N/A INTRINSIC
low complexity region 198 212 N/A INTRINSIC
low complexity region 219 254 N/A INTRINSIC
low complexity region 279 289 N/A INTRINSIC
low complexity region 301 326 N/A INTRINSIC
low complexity region 345 373 N/A INTRINSIC
Pfam:SK_channel 380 493 2.2e-51 PFAM
transmembrane domain 516 535 N/A INTRINSIC
Pfam:Ion_trans_2 572 658 2.2e-14 PFAM
CaMBD 672 748 6.51e-51 SMART
coiled coil region 751 784 N/A INTRINSIC
low complexity region 815 839 N/A INTRINSIC
Predicted Effect silent
SMART Domains Protein: ENSMUSP00000129659
Gene: ENSMUSG00000054477

DomainStartEndE-ValueType
low complexity region 14 24 N/A INTRINSIC
low complexity region 36 61 N/A INTRINSIC
low complexity region 80 108 N/A INTRINSIC
Pfam:SK_channel 115 215 1.4e-36 PFAM
Pfam:Ion_trans_2 169 254 9.5e-15 PFAM
CaMBD 267 343 6.51e-51 SMART
coiled coil region 346 379 N/A INTRINSIC
low complexity region 410 434 N/A INTRINSIC
Predicted Effect silent
SMART Domains Protein: ENSMUSP00000139350
Gene: ENSMUSG00000054477

DomainStartEndE-ValueType
low complexity region 62 76 N/A INTRINSIC
low complexity region 84 90 N/A INTRINSIC
low complexity region 98 114 N/A INTRINSIC
low complexity region 129 141 N/A INTRINSIC
low complexity region 158 180 N/A INTRINSIC
low complexity region 198 212 N/A INTRINSIC
low complexity region 219 254 N/A INTRINSIC
low complexity region 279 289 N/A INTRINSIC
low complexity region 301 326 N/A INTRINSIC
low complexity region 345 373 N/A INTRINSIC
Pfam:SK_channel 380 498 2.9e-60 PFAM
transmembrane domain 516 535 N/A INTRINSIC
Pfam:Ion_trans_2 573 659 1.8e-14 PFAM
CaMBD 672 748 6.51e-51 SMART
coiled coil region 751 784 N/A INTRINSIC
low complexity region 815 839 N/A INTRINSIC
Predicted Effect silent
Predicted Effect silent
Meta Mutation Damage Score Not available question?
Is this an essential gene? Probably nonessential (E-score: 0.155) question?
Phenotypic Category Autosomal Recessive
Candidate Explorer Status loading ...
Single pedigree
Linkage Analysis Data
Penetrance 100% 
Alleles Listed at MGI

All alleles(4) : Targeted, knock-out(1) Targeted, other(2) Chemically induced(1)

Lab Alleles
AlleleSourceChrCoordTypePredicted EffectPPH Score
IGL00087:Kcnn2 APN 18 45725303 missense probably damaging 0.98
IGL00341:Kcnn2 APN 18 45810138 splice site probably benign
IGL01317:Kcnn2 APN 18 45693694 splice site probably null
IGL02121:Kcnn2 APN 18 45694340 missense probably damaging 0.98
IGL02561:Kcnn2 APN 18 45725259 missense possibly damaging 0.59
IGL03000:Kcnn2 APN 18 45693635 missense probably damaging 0.97
IGL03116:Kcnn2 APN 18 45788273 missense probably damaging 1.00
IGL03155:Kcnn2 APN 18 45818382 missense probably damaging 0.99
IGL03289:Kcnn2 APN 18 45810111 missense probably damaging 1.00
IGL03343:Kcnn2 APN 18 45810026 missense probably damaging 0.97
I2288:Kcnn2 UTSW 18 45808340 intron probably benign
R0256:Kcnn2 UTSW 18 45725472 missense probably damaging 0.98
R0310:Kcnn2 UTSW 18 45693585 missense probably damaging 1.00
R0464:Kcnn2 UTSW 18 45693426 missense probably damaging 0.99
R0468:Kcnn2 UTSW 18 45692538 missense possibly damaging 0.96
R0485:Kcnn2 UTSW 18 45693215 missense probably benign 0.06
R0722:Kcnn2 UTSW 18 45692543 missense possibly damaging 0.73
R0898:Kcnn2 UTSW 18 45692543 missense possibly damaging 0.73
R1567:Kcnn2 UTSW 18 45803401 splice site probably null
R4543:Kcnn2 UTSW 18 45692715 missense probably benign 0.00
R4720:Kcnn2 UTSW 18 45816187 missense possibly damaging 0.78
R4732:Kcnn2 UTSW 18 45693416 missense possibly damaging 0.94
R4733:Kcnn2 UTSW 18 45693416 missense possibly damaging 0.94
R4801:Kcnn2 UTSW 18 45818334 splice site probably benign
R4844:Kcnn2 UTSW 18 45816187 missense possibly damaging 0.78
R4927:Kcnn2 UTSW 18 45692798 missense probably benign 0.01
R5011:Kcnn2 UTSW 18 45818352 missense possibly damaging 0.86
R5108:Kcnn2 UTSW 18 45725122 missense probably damaging 0.99
R5805:Kcnn2 UTSW 18 45816198 missense probably damaging 0.98
R5841:Kcnn2 UTSW 18 45692463 missense probably benign
R5888:Kcnn2 UTSW 18 45725412 missense probably damaging 0.98
R5926:Kcnn2 UTSW 18 45818351 missense probably benign 0.01
R6552:Kcnn2 UTSW 18 45693165 missense probably benign 0.00
R6882:Kcnn2 UTSW 18 45692505 missense possibly damaging 0.53
R6999:Kcnn2 UTSW 18 45725444 missense probably damaging 0.99
R7324:Kcnn2 UTSW 18 45693138 missense probably benign
R7509:Kcnn2 UTSW 18 45816187 missense probably benign 0.32
R7667:Kcnn2 UTSW 18 45692505 missense possibly damaging 0.53
R8064:Kcnn2 UTSW 18 45692426 start codon destroyed probably benign 0.01
R8122:Kcnn2 UTSW 18 45810005 missense probably damaging 0.99
R8730:Kcnn2 UTSW 18 45725139 missense possibly damaging 0.75
R8768:Kcnn2 UTSW 18 45692502 missense possibly damaging 0.53
R9183:Kcnn2 UTSW 18 45694379 missense probably damaging 0.99
R9278:Kcnn2 UTSW 18 45725446 missense probably damaging 0.96
R9597:Kcnn2 UTSW 18 45816149 missense probably benign 0.16
R9773:Kcnn2 UTSW 18 45788365 missense probably damaging 0.99
Mode of Inheritance Autosomal Recessive
Local Stock Embryos, Sperm, gDNA
MMRRC Submission 030543-UCD
Last Updated 2018-05-22 9:34 AM by Anne Murray
Record Created unknown
Record Posted 2008-07-29
Phenotypic Description
The jitter mutation was identified among G3 N-ethyl-N-nitrosourea (ENU)-mutagenized mice. Homozygous mice exhibit a tremor and a gait disorder.  The degree of tremor varies and is often accompanied by “stiff” and deliberate hind foot placement on movement, particularly in older animals.  The phenotype is apparent in mice three weeks of age, at which time they are significantly smaller than their littermates.  The mutants also exhibit a hunched posture and lack-luster coat seen in mice as young as three months of age.
 
Both heterozygous males and females are fertile, but male homozygotes do not breed.  Female homozygotes are able to breed.  Jitter mice display normal macrophage responses to Toll-like receptor ligands, double-stranded DNA, the adjuvant alum, and viral infections (TLR Signaling Screen, Double-stranded DNA Macrophage Screen, NALP3 Inflammasome Screen, Ex Vivo Macrophage Screen for Control of Viral Infections), normal proportions of immunological cell types, and normal natural killer (NK) and T cell cytotoxicity (In Vivo NK Cell and CD8+ Cell Cytotoxicity Screen).  They also display a normal humoral immune response to model antigens encoded by a recombinant suicide vector based on the Semliki Forest Virus (rSFV).
Nature of Mutation
The jitter mutation was mapped to Chromosome 18, and corresponds to a T to C transition at position 503 of the Kcnn2 gene, in exon 3 of 9 total exons.
 
487 TTAGCTCTGAAATGCCTTATCAGTCTCTCCACG
163 -L--A--L--K--C--L--I--S--L--S--T-
 
The mutated nucleotide is indicated in red lettering, and results in a leucine to proline change at amino acid 168 in the standard form of the SK2 protein and amino acid 443 in the long form of the SK2 protein.
Illustration of Mutations in
Gene & Protein
Protein Prediction
Figure 1. Domain and typography of the subunit structure of SK2. Cylinders represent a-helical transmembrane domains with green indicating the pore-lining segments. The C-terminal calmodulin binding domain is shown (CaMBD) in pink. Major sites of PKA phosphorylation are indicated by the yellow circles. Orange circles indicate amino acids critical for apamine sensitivity. The location of the jitter mutation is shown in red. Four SK subunits combine to form the full channel. 
KCNN2 or SK2 is a member of the small/intermediate conductance calcium (Ca2+)-activated potassium (K+) channel protein superfamily that includes SK1-4 (1).  SK2 is an integral membrane protein that forms a voltage-independent calcium-activated channel with three other SK subunits.  The resultant K+ channel is usually heteromeric (2-5), giving rise to structural and functional diversity amongst SK channels in various tissues.  The SK subunits have six transmembrane α helices (S1-S6) with cytoplasmic N- and C-terminal domains (Figure 1).  The loops between transmembrane domains 2 and 3 and 4 and 5 are also cytoplasmic.  A membrane-reentrant extracellular loop called the “pore loop” is located between the S5 and S6 helices in each of the four subunits.  Although SK channels are otherwise structurally dissimilar from voltage-gated K+ channels, the architecture of the pore is quite similar.  The pore loops line the outer entry to the pore and contain amino acids that serve as the ion selectivity filter (2).  The transmembrane domains among these proteins are highly conserved (1). 
 
Figure 2. Crystal structure of CaMBD/Ca2+/CaM complex. CaMD subunits are in orange and teal, CaM molecules are in blue and pink, and Ca2+ ions are in green. UCSF Chimera structure is based on PDB 1G4Y, Schumacher et al, Nature 410, 1120-1124 (2001). Click on each 3D structure to view it rotate.
Human SK2 (hSK2) is 97% identical to rat SK2 and 95% identical to the mouse protein, with most of the differences found in the N-terminus (1;6).  SK2 contains several consensus cAMP-dependent protein kinase (PKA), casein kinase II and protein kinase C phosphorylation sites at the N- and C-terminus.  The major sites of PKA phosphorylation occur at Ser568-570 (6;7).  Several SK2 isoforms have been identified; SK2-std (standard form) in the mouse is 49 kDa, SK2-L (long form) contains an N-terminal extension and is 78 kDa, and a newly identified SK2-Sh (short form) is alternatively spliced at exon 3 and therefore lacks 140 amino acids, which include transmembrane domains S3, S4 and S5, compared to SK2-Std (5;8).  The N-terminal extension of SK2-L is cysteine-rich and mediates disulfide bond formation between SK2-L subunits or with heterologous proteins (5).
 
The SK channels are sensitive to the bee venom peptide toxin, apamin, an 18-amino acid peptide with two internal disulfide bridges that hold the peptide in a tight tertiary conformation(1;9).  The amino acids that mediate apamin sensitivity are an aspartic acid D335 and an asparagine N362 that reside on opposite sides of the pore (2).  No other class of K+ channels is blocked by this drug, and among the cloned K+ channels, the residues that endow sensitivity are present at those positions only in SK2 and SK3 channels.  These same residues also mediate differential SK channel sensitivity to the nicotinic acetylcholine receptor antagonist D-tubocurarine, a member of the curare toxins (2), and are likely to be the determinants for block by other selective SK blockers.  In addition to these two amino acids, a single amino acid S239 situated in the extracellular loop between the transmembrane domains S3 and S4, also strongly affects apamin sensitivity (10).  SK2 is highly sensitive to apamin and D-tubocurarin, whereas SK1 channels are the least sensitive (2;11).  SK3 channels have intermediate sensitivity to these toxins.
 
The SK membrane channels are heteromeric complexes consisting of pore-forming α-subunits (generally SK1-3) and the Ca2+-binding protein calmodulin (CaM).  CaM binds constitutively to the SK channel through the CaM-binding domain (CaMBD), which is located in an intracellular region of the α-subunit immediately carboxy-terminal to the pore (amino acids 391-484) (12;13).  This region is the most conserved intracellular domain in SK channels (12).  Channel opening is triggered when Ca2+ binds the EF hands in the N-lobe of CaM (13).  An EF hand is a helix-turn-helix structural domain consisting of two roughly perpendicular α helices found in many calcium-binding proteins (14).  Upon Ca2+ binding to CaM, the CaMBDs of two SK2 molecules form an elongated dimer with a CaM molecule bound at each end; each CaM wraps around three α helices, two from one CaMBD subunit and one from the other.  In the complex, the CaMBD consists of two long α helices, α1 (residues 413–440 for rat, 406-436 for mouse) and α2 (residues 446–489 for rat, 440-483 for mouse), connected by a loop (residues 441–445 for rat, 435-439 for mouse).  Binding of Ca2+ to CaM molecules results in a conformational change that is propagated to the S6 pore helices in the gate region of the SK channel, causing channel opening and influx of potassium (15).
 
The jitter mutation results in a leucine to proline change within the second transmembrane helix of the SK2 potassium channel.  It is unknown whether this protein is expressed and localized normally.
Expression/Localization
SK2 is a transmembrane protein expressed throughout the central nervous system (CNS) as well as many peripheral tissues in both rodents and humans.  Western blot analysis of mouse hippocampal tissue revealed a 47 kDa protein product as predicted for SK2-Sh along with a 64 kDa band representing the standard SK2 isoform (8).  At the cellular level in the mouse brain, SK2 immunoreactivity was primarily localized to somatic and dendritic structures (16).  Immunohistochemistry revealed that in the mouse brain SK2-L and SK2-Std are expressed in similar but not identical patterns.  In contrast to the diffuse, uniform surface distribution of SK2-Std, SK2-L channels cluster into sharply defined, distinct puncta suggesting that the extended cysteine-rich N-terminal domain mediates this process (see Protein Prediction).  Outside of the brain, RTPCR and western blot studies show SK2 is expressed in the mouse heart in cardiac myocytes, with expression levels of SK2 higher in atrial versus ventral myocytes (17-19).  Both RT-PCR as well as immunohistochemistry showed that SK channels, including SK2, are expressed in pancreatic islets including the insulin-producing β-cells.  In islets, SK2 was present intracellularly in a punctate pattern, and was also present in the nuclear membrane or an area near the nuclear membrane (20).  SK2 was also demonstrated to be present in the smooth muscle of the bladder (21), and is transiently expressed in immature inner hair cells (22;23).  In guinea pig, SK2 is expressed in enteric neurons (24).
 
Northern analysis in rats found SK2 transcripts in the brain and adrenal glands (1).  In situ hybridization studies suggest SK2 is the most widely and strongly expressed SK channel in the rat brain, and is highest in the hippocampus with lower levels in the olfactory bulb and the anterior olfactory nucleus, the granular layer of the cerebellum, the reticular nucleus of the thalamus (Th), and the pontine nucleus (Pn) (1;25).  SK2 is also expressed in all vestibular neurons (26).  In rats, SK2 channels have also been identified in numerous other tissues including the retina (27), and the cochlear inner and outer hair cells (28;29). 
 
In human tissues, Northern blot analysis revealed a major 2.5 kb hSK2 transcript in leukemic Jurkat T cells, liver, kidney, and brain with the strongest signals in the liver and brain.  A higher molecular weight transcript of 4.4 kb was found in heart and skeletal muscle, while a 1.3 kb transcript was observed in brain and liver.  hSK2 transcripts were also found in melanocytes and fetal heart (6).  Quantitative RT-PCR suggests human SK2 is widely expressed with transcripts distributed across the CNS and periphery, and highest amounts found in the pituitary gland and the liver (30).   RT-PCR and Western blots show hSK2 is also expressed in cardiac myocytes (18).
Background
Figure 3. Four SK2 proteins, each bound to one CaM protein, form the voltage-independent calcium-activated SK2 channel.  CaM is constitutively bound to SK2, and calcium binding to CaM results in a conformational change in helix S6 of SK2, causing channel opening.  In hippocampal neurons, SK channels are tightly coupled to L-type voltage-dependent Ca2+ channels and N-methyl-D-aspartate receptors (NMDAR), and reduce NMDAR-dependent calcium influx.  Successful induction of LTP results in endocytosis of SK2 channels.
 
Calcium-activated potassium channels respond to changes in intracellular calcium concentration, and couple calcium metabolism to potassium flux and membrane excitability (Figure 3).  Based on their electrophysiological properties, calcium-activated potassium channels are classified as large conductance, calcium- and voltage-gated channels, intermediate conductance, voltage-independent channels (SK4), and small conductance, voltage-independent channels (SK1-3) (31).  Small-conductance calcium-activated K+ channels are voltage independent and activated solely by intracellular calcium (32). Functional SK channels are heteromeric complexes with constitutively bound calmodulin, and channel opening occurs in response to binding of calcium to calmodulin (4).  SK2 was first identified in 1996 when rat SK2 was cloned from rat brain (1).  Human SK2 was then isolated from a Jurkat T-cell cDNA library.  Functional analysis showed that KCNN2 supports a K+ current that is sensitive to apamin, scyllatoxin, and tubocurarine, and is insensitive to charybdotoxin (6).
 
In neurons, SK channels are activated by the transient elevation of intracellular Ca2+ that occurs during an action potential (AP).  Their activity contributes to a prolonged afterhyperpolarization (AHP) during which the return to baseline reflects the decay of intracellular Ca2+ levels.  The AHP may persist for several seconds and can modulate the firing pattern of the neuron.  The AHP has several components.  The fast component helps to repolarize the action potential and regulates spike intervals, whereas the slower components underlie spike-frequency adaptation.  The fast AHP component is predominantly attributable to voltage-dependent K+ channels, whereas SK channels are thought to contribute to the slow components of the AHP.  The increase in intracellular Ca2+ evoked by AP firing decays slowly, allowing SK channel activation to generate a long lasting hyperpolarization that protects the cell from the deleterious effects of continuous tetanic activity (32).  SK channels regulate neuronal firing in the hippocampus, substantia nigra, thalamus and the cerebellum (32-34).    
 
Intracerebroventricular injections of the specific SK channel blocker apamine in rats disturbed the circadian cycle and disrupted normal sleep patterns (35).  Similarly, SK2 knockout mice exhibit disrupted sleep due to abnormal modification of T-type Ca2+ channels (T channels) in thalamic dendrites resulting in lack of neuronal oscillations that are typical during sleep (34).  Apamine injections into rats also facilitated the induction of hippocampal synaptic plasticity and enhanced hippocampal learning (36), while transgenic mice overexpressing SK2 exhibit marked defects in hippocampal memory and synaptic plasticity at the encoding level (37;38).  These results suggest hippocampal-dependent synaptic plasticity and memory are modulated by SK2.  Through knockout studies of SK1-3 in mice, it was determined that only SK2 subunits are necessary for the apamin-sensitive currents in CA1 hippocampal neurons (39).  SK channels in CA1 neurons have been shown to be tightly coupled to L-type voltage-dependent Ca2+ channels (40).  Other studies have shown that SK channels in hippocampal neurons are coupled to calcium entry through N-methyl-D-aspartate (NMDA) receptors (41;42).  Activity-dependent changes in synaptic strength underlie the cellular mechanisms of learning and memory (43).  At Schaffer collateral-to CA1 synapses, protocols that induce long term potentiation (LTP) of synaptic strength affect the postsynaptic cell through a process that is dependent upon NMDA receptor activity (44).  SK2 channels expressed in dendritic spines are activated by synaptically driven Ca2+ influx through NMDA receptors (42).  The repolarizing effect of SK2 channel activity opposes the depolarizing effect of AMPA (an artificial glutamate analogue) receptors in the postsynaptic density (PSD) of the spine.  Increases in AMPA receptor number and biophysical properties have been shown to underlie the changes caused by LTP inducing protocols acting through PKA and calcium/calmodulin-dependent kinase II (45;46).  LTP induction in mouse hippocampus abolishes SK2 channel activity in the potentiated synapses due to SK2 channel internalization from the PSD.  SK2 endocytosis occurs upon phosphorylation of the SK2 C-terminal domain by PKA (47).
 
SK channels also play roles in the function of other tissues.  The atrioventricular node (AVN) is a highly specialized pacemaking tissue located at the junction of the right atrium and ventricle.  It is the only electrical connection between atria and ventricles and provides the critical delay between atrial and ventricular contraction allowing proper atrial emptying before the start of the ventricular contraction (48).  In the heart, SK2 is expressed in cardiac myocytes, especially atrial myocytes that are accordingly more sensitive to the effects of apamin.  In contrast to the hyperpolarization effects of SK channels in neurons, in the heart SK channels contribute markedly toward the late phase of the cardiac repolarization.  This late phase of the cardiac AP is susceptible to aberrant excitation (18).  Similar to CA1 hippocampal neurons, SK2 channels in cardiac myocytes integrate changes in intracellular calcium concentration with changes in potassium-conductance and membrane potential by associating with L-type Ca2+ channels.  Recent data suggests this occurs in cardiac myocytes through association of SK2 with the cytoskeletal protein α-actinin2.  The lack of the L-type Ca2+ channel Cav1.3 in mouse myocytes causes abnormal SK2 function resulting in prolongation of repolarization and atrial arrhythmias (49).  Overexpression of SK2 in transgenic mice shortened the spontaneous action potentials of the AVN cells and increased the firing frequency, while ablation of SK2 in the knockout mouse model resulted in the opposite effects (48).  SK2 also plays a key role in regulating the frequency and the shaping urinary bladder smooth muscle (UBSM) APs, thus modulating contractility of the UBSM.  SK2 has been shown to be critical in modulating the APs of immature inner hair cells (IHC) of the mammalian cochlea and enteric neurons via functional interactions with nicotinic acetylcholine receptors (nAChRs) (23;24;28).  Although SK2 is expressed in pancreatic islets, it does not play a major role in the modification of glucose-induced insulin secretion by apamin in mouse β-cells (20). 
 
In the immune system, SK channels play a role in T-lymphocyte activation by helping to maintain sustained Ca2+ influx that activates Ca2+-dependent signaling pathways and cytokine production in these cells (50).  SK2 was identified as being the major SK channel in the human T-lymphocyte cell line Jurkat, but SK4 is the SK channel expressed in activated primary human T-lymphocytes (6;50).  Additionally, granulysin-mediated apoptosis of mammalian cells is dependent on an increase in intracellular Ca2+ and a decrease in intracellular K+ in the target cell resulting from the function of Ca2+ and K+ channels, including apamin-sensitive SK channels.  Granulysin, a molecule present in the granules of activated T-lymphocytes and natural killer (NK) cells, is cytolytic against microbes and tumors (51).  These results suggest that SK channels, including SK2, contribute to the function of immune cells.
 
Transcriptional regulation of SK2 is not well understood, but examination of the SK2-Std promoter found a glucocorticoid response element (GRE) that binds to the glucocorticoid receptor (GR), as well as two functional nuclear factor-κB (NF-κB) response elements.  In vitro experiments suggested that the SK2 reporter is responsive to both GR and MR (mineralcorticoid receptor) and NF-κB stimulation (52).
Putative Mechanism
Recently, the mouse neurological mutant frissonant (fri) was discovered to carry a large deletion in the 5’ region of the Kcnn2 gene, which disrupts both the first and second coding exons (53).  Fri mice still express reduced levels of Kcnn2 transcripts, but these transcripts give rise to truncated proteins that are not likely to be functional.  The fri mutant phenotype is characterized by constant rapid tremor and locomotor instability, and also displays size and male fertility defects similar to jitter mice (53;54).  It is thought that the tremor and locomotive defects displayed by fri mice may be due to alterations of the firing properties of central vestibular nuclei neurons, which are known to control gaze, posture and locomotion through the vestibulo-oculomotor and vestibulospinal pathways.  In vivo applications of apamin modified the firing properties of some of these neurons (55), and resulted in high-frequency oscillations of the head, trunk, and limbs.  The central vestibular neurons of frissonant mice revealed permanent alterations of the AHP and firing behavior (53).
 
In addition to the apparent locomotor and tremor defect, fri mice have been reported to suffer a short-term memory deficit (54).  This is interesting considering the memory and learning defects exhibited by mice overexpressing SK2 that are caused by an increase in excitatory postsynaptic potentials and a strong reduction of synaptic plasticity (37).  Because they have motor and memory defects and display improvement upon treatment with dopamine, fri mice are suggested to be a mouse model of Parkinson disease (PD; OMIM #168600) (54). Impaired function of dopaminergic neurons (DA) is associated with PD and schizophrenia (OMIM #181500), and SK channels modulate the firing pattern of DA neurons.  However, immunohistochemistry and pharamacology profiles identify SK3 channels as the predominant mediators of SK effects in these neurons (32).   
 
The amino acid change in the SK2 protein in jitter mice occurs in a transmembrane helix of SK2, and results in the substitution of a leucine for a proline.  Proline residues are known to destabilize secondary structures including alpha-helixes (56).  Thus, the addition of a proline into a transmembrane helix of SK2 may disrupt the formation of the potassium channel and prevent its appropriate localization in the plasma membrane.  The similarity of the jitter phenotypes with frissonant mice, which carry a large deletion of the Kcnn2 gene and are not likely to express functional protein (53), suggests that the SK2 protein in jitter mice is also non-functional.  Interestingly, the phenotypic defects seen in fri and jitter mice have not been reported for the mouse SK2 knockout mouse (39).  This discrepancy suggests the possibility that the frissonant and jitter mutations somehow cause a novel defect or that genetic background may play a role.  However, it is also possible that these specific defects do exist in the SK2 knockout mice, but were not reported.
Primers Primers cannot be located by automatic search.
Genotyping
Jitter genotyping is performed by amplifying the region containing the mutation using PCR, followed by sequencing of the amplified region to detect the single nucleotide change.  
 
Primers for PCR amplification
Jitter(F): 5’- GAGCAACTTCCTCTAGGCTTTAGCG -3’
Jitter(R): 5’- GCAAGGCTACTCACTTCCTCTGAC -3’
 
PCR program
1) 94°C             2:00
2) 94°C             0:30
3) 56°C             0:30
4) 72°C             1:00
5) repeat steps (2-4) 29X
6) 72°C             7:00
7) 4°C               ∞
 
Primers for sequencing
Jitter_seq(F): 5’- CCTCTAGGCTTTAGCGAGTCAG -3'
Jitter_seq(R): 5’- AGAAAGATCTGCCTGTTGCC -3’
 
The following sequence of 1172 nucleotides (from Genbank genomic region NC_000084.5 for linear DNA sequence of Kcnn2) is amplified:
 
 795                gagcaa cttcctctag gctttagcga gtcaggtacc ttgtttcagt
 841 ccttggtggt gcgtagcccg cagccaaccc acgagttttc ccttgttcct ggctcctctc
 901 acggagcatt atggccaaat aacctgcatc ccagagccaa aacagattgc cccctcccga
 961 gtcccctacc ttgaattcag gtccacgtgc tcggaactga cttttatggc ctggaaagag
1021 attggaagtg cttctttctt aaagtgttcc atctaactgt gttgcaggcg tcgctgtatt
1081 ctttagctct gaaatgcctt atcagtctct ccacgatcat cctgcttggt ctgatcatcg
1141 tgtaccacgc cagggaaata caggtaacac aggctccact gttttctgaa taaccagaag
1201 ccatgcaggc agcataggag aaaagcaaga cagcaagggg cctttaccaa gcagctgtgt
1261 ccttgcttga ggttacagaa gacacatgca ctgttatctc agcacctgac ctgtccttcc
1321 agaaagctaa acaaacaaac aagtcaacac agcagggcaa caggcagatc tttctgagat
1381 atatttgata gaatcttaag attttcccca acttcttcag gctggtacac ttctaccaga
1441 caaatgtttt taaaggagcg gtacacaata tcctgaatct gtgcagcagt gtgtgttctt
1501 gtttaagaca cctttttaaa aggagtaagt cattagggga ggaggccttg ccaatctgga
1561 ttgcctataa ttataatata agaaaattgg ttcactgctt ctatcaacat gggaagagca
1621 cctcccctcc ccaaacttct aacgcatttt acaacagctt atttagttca taaagcctgt
1681 gtaggtatta gtgtagtccg agcattttaa atgtcacttg agagtatttg gagtgggtaa
1741 tgatagacga aagcacactt ggtcgaattt ttaatattag gacagtatat agattcttca
1801 gtgcagtcct cacgatggtg gcattttgag attcttccag aggtcctctg tggtcctctg
1861 ctgtgcttta agcctgggtc actttgactt gaagcctgga agatagagaa tgagtctttg
1921 acttcgtttt cagatggaaa cagtcagagg aagtgagtag ccttgc
 

 PCR primer binding sites are underlined; sequencing primer binding sites are highlighted in gray; the mutated T is shown in red text.

References
Science Writers Nora G. Smart
Illustrators Diantha La Vine
AuthorsAmanda L. Blasius, Xin Du, Bruce Beutler
Edit History
2011-09-12 5:04 PM (current)
2011-01-07 9:14 AM
2010-10-05 3:40 PM
2010-10-05 3:40 PM
2010-01-18 12:00 AM