Phenotypic Mutation 'Roomba' (pdf version)
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AlleleRoomba
Mutation Type critical splice donor site
Chromosome3
Coordinate135,612,412 bp (GRCm38)
Base Change A ⇒ T (forward strand)
Gene Nfkb1
Gene Name nuclear factor of kappa light polypeptide gene enhancer in B cells 1, p105
Synonym(s) p50 subunit of NF kappaB, nuclear factor kappaB p50, NF-kappaB, NF-kappaB p50, p50, p50/p105, NF kappaB1
Chromosomal Location 135,584,655-135,691,547 bp (-)
MGI Phenotype Strain: 1857225
FUNCTION: [Summary is not available for the mouse gene. This summary is for the human ortholog.] This gene encodes a 105 kD protein which can undergo cotranslational processing by the 26S proteasome to produce a 50 kD protein. The 105 kD protein is a Rel protein-specific transcription inhibitor and the 50 kD protein is a DNA binding subunit of the NF-kappa-B (NFKB) protein complex. NFKB is a transcription regulator that is activated by various intra- and extra-cellular stimuli such as cytokines, oxidant-free radicals, ultraviolet irradiation, and bacterial or viral products. Activated NFKB translocates into the nucleus and stimulates the expression of genes involved in a wide variety of biological functions. Inappropriate activation of NFKB has been associated with a number of inflammatory diseases while persistent inhibition of NFKB leads to inappropriate immune cell development or delayed cell growth. Alternative splicing results in multiple transcript variants encoding different isoforms, at least one of which is proteolytically processed. [provided by RefSeq, Feb 2016]
PHENOTYPE: Homozygous null mice have a decreased survivor rate, abnormal T cell development and decreased number of peripheral T cells, abnormal humoral responses with decreased immunoglobulin class switching, exhibit mild organ inflammation, and are susceptible toboth bacterial infections and hearing loss. [provided by MGI curators]
Accession Number

NCBI RefSeq: NM_008689; MGI:97312

Mapped Yes 
Amino Acid Change
Institutional SourceBeutler Lab
Gene Model predicted gene model for protein(s): [ENSMUSP00000029812] [ENSMUSP00000128345] [ENSMUSP00000143601]
SMART Domains Protein: ENSMUSP00000029812
Gene: ENSMUSG00000028163

DomainStartEndE-ValueType
Pfam:RHD 42 240 2.9e-75 PFAM
IPT 247 348 1.14e-22 SMART
low complexity region 368 414 N/A INTRINSIC
ANK 538 568 2.27e1 SMART
ANK 577 606 1.11e-2 SMART
ANK 610 640 2.47e0 SMART
ANK 646 675 5.53e-3 SMART
ANK 680 710 1.9e-1 SMART
ANK 714 743 2.18e-1 SMART
DEATH 801 888 1.9e-19 SMART
low complexity region 890 902 N/A INTRINSIC
Predicted Effect probably null
SMART Domains Protein: ENSMUSP00000114798
Gene: ENSMUSG00000028163

DomainStartEndE-ValueType
low complexity region 8 54 N/A INTRINSIC
Blast:IPT 55 156 4e-22 BLAST
ANK 178 208 2.27e1 SMART
ANK 217 246 1.11e-2 SMART
ANK 250 280 2.47e0 SMART
ANK 286 315 5.53e-3 SMART
ANK 320 350 1.9e-1 SMART
ANK 354 383 2.18e-1 SMART
Blast:DEATH 441 505 1e-34 BLAST
PDB:2DBF|A 442 505 5e-32 PDB
Predicted Effect probably benign
SMART Domains Protein: ENSMUSP00000128345
Gene: ENSMUSG00000028163

DomainStartEndE-ValueType
Pfam:RHD_DNA_bind 42 240 2.9e-75 PFAM
IPT 247 348 1.14e-22 SMART
low complexity region 368 414 N/A INTRINSIC
ANK 538 568 2.27e1 SMART
ANK 577 606 1.11e-2 SMART
ANK 610 640 2.47e0 SMART
ANK 646 675 5.53e-3 SMART
ANK 680 710 1.9e-1 SMART
ANK 714 743 2.18e-1 SMART
DEATH 801 888 1.9e-19 SMART
low complexity region 890 902 N/A INTRINSIC
Predicted Effect probably null
SMART Domains Protein: ENSMUSP00000143601
Gene: ENSMUSG00000028163

DomainStartEndE-ValueType
Pfam:RHD_DNA_bind 42 90 2.5e-19 PFAM
Predicted Effect probably benign
Phenotypic Category
Phenotypequestion? Literature verified References
DSS: sensitive day 10
FACS central memory CD8 T cells in CD8 T cells - increased
T-dependent humoral response defect- decreased antibody response to rSFV
Total IgE After 2nd OVA/Alum Challenge (day 7) - decreased 7834752
Penetrance  
Alleles Listed at MGI

All alleles(83) : Chemically induced (ENU)(1) Chemically induced (other)(1) Gene trapped(74) Radiation induced(1) Targeted(6)

Lab Alleles
AlleleSourceChrCoordTypePredicted EffectPPH Score
IGL01293:Nfkb1 APN 3 135590839 missense probably damaging 1.00
IGL01345:Nfkb1 APN 3 135594981 missense probably damaging 1.00
IGL01629:Nfkb1 APN 3 135601467 missense probably benign
IGL02216:Nfkb1 APN 3 135594963 missense probably damaging 0.98
IGL02273:Nfkb1 APN 3 135605207 missense probably benign 0.01
IGL02508:Nfkb1 APN 3 135590818 missense probably damaging 0.99
IGL03095:Nfkb1 APN 3 135618830 missense possibly damaging 0.48
Finlay UTSW 3 135595053 nonsense probably null
kookaburra UTSW 3 135626611 nonsense probably null
Murgatroyd UTSW 3 135626710 missense
puff UTSW 3 135595053 nonsense
R0026:Nfkb1 UTSW 3 135591573 missense probably damaging 1.00
R0047:Nfkb1 UTSW 3 135595053 nonsense probably null
R0989:Nfkb1 UTSW 3 135589396 missense probably benign 0.00
R1210:Nfkb1 UTSW 3 135594927 missense probably benign 0.03
R1661:Nfkb1 UTSW 3 135594957 missense probably damaging 1.00
R1665:Nfkb1 UTSW 3 135594957 missense probably damaging 1.00
R1725:Nfkb1 UTSW 3 135667758 missense probably damaging 1.00
R1984:Nfkb1 UTSW 3 135615349 missense possibly damaging 0.81
R1985:Nfkb1 UTSW 3 135615349 missense possibly damaging 0.81
R2154:Nfkb1 UTSW 3 135601479 missense probably benign 0.44
R2281:Nfkb1 UTSW 3 135601521 missense probably damaging 1.00
R2409:Nfkb1 UTSW 3 135613943 missense possibly damaging 0.93
R2504:Nfkb1 UTSW 3 135589329 missense possibly damaging 0.51
R4032:Nfkb1 UTSW 3 135594349 missense possibly damaging 0.63
R4232:Nfkb1 UTSW 3 135603770 missense probably damaging 1.00
R4936:Nfkb1 UTSW 3 135613982 missense probably damaging 0.97
R5085:Nfkb1 UTSW 3 135603807 missense probably benign 0.36
R5262:Nfkb1 UTSW 3 135612412 critical splice donor site probably null
R5384:Nfkb1 UTSW 3 135612542 missense possibly damaging 0.95
R5385:Nfkb1 UTSW 3 135612542 missense possibly damaging 0.95
R5434:Nfkb1 UTSW 3 135626611 nonsense probably null
R5663:Nfkb1 UTSW 3 135603851 missense possibly damaging 0.88
R5865:Nfkb1 UTSW 3 135603780 missense probably damaging 1.00
R6006:Nfkb1 UTSW 3 135603761 nonsense probably null
R6013:Nfkb1 UTSW 3 135626684 missense possibly damaging 0.86
R6234:Nfkb1 UTSW 3 135626710 missense possibly damaging 0.72
R6785:Nfkb1 UTSW 3 135615303 missense probably benign
X0050:Nfkb1 UTSW 3 135606623 missense probably damaging 1.00
Mode of Inheritance Autosomal Semidominant
Local Stock
Repository
Last Updated 2018-07-20 12:08 PM by Diantha La Vine
Record Created 2017-07-06 2:21 PM by Bruce Beutler
Record Posted 2017-08-18
Phenotypic Description

Figure 1. Roomba mice exhibit diminished T-dependent IgG responses to recombinant Semliki Forest virus (rSFV)-encoded β-galactosidase (rSFV-β-gal). IgG levels were determined by ELISA. Normalized data are shown. Abbreviations: WT, wild-type; REF, homozygous reference mice; HET, heterozygous variant mice; VAR, homozygous variant mice. Mean (μ) and standard deviation (σ) are indicated.

Figure 2. Roomba mice exhibited reduced total IgE levels in the serum. IgE levels were determined by ELISA. Normalized log data are shown. Abbreviations: WT, wild-type; REF, homozygous reference mice; HET, heterozygous variant mice; VAR, homozygous variant mice. Mean (μ) and standard deviation (σ) are indicated.

Figure 3. Roomba mice exhibit decreased frequencies of peripheral central memory CD8 T cells in CD8 T cells. Flow cytometric analysis of peripheral blood was utilized to determine T cell frequency. Normalized data are shown. Abbreviations: WT, wild-type; REF, homozygous reference mice; HET, heterozygous variant mice; VAR, homozygous variant mice. Mean (μ) and standard deviation (σ) are indicated.

The Roomba phenotype was identified among N-Nitroso-N-ethylurea (ENU)-mutagenized G3 mice of the pedigree R5262, some of which exhibited a diminished T-dependent IgG response to recombinant Semliki Forest virus (rSFV)-encoded β-galactosidase (rSFV-β-gal; Figure 1). Some mice exhibited reduced total IgE levels in the serum (Figure 2) as well as reduced frequencies of central memory CD8 T cells in CD8 T cells in the peripheral blood (Figure 3).

Nature of Mutation

Figure 4. Linkage mapping of the reduced total IgE in the serum using an additive model of inheritance. Manhattan plot shows -log10 P values (Y-axis) plotted against the chromosome positions of 61 mutations (X-axis) identified in the G1 male of pedigree R5262. Log phenotype data are shown for single locus linkage analysis without consideration of G2 dam identity. Horizontal pink and red lines represent thresholds of P = 0.05, and the threshold for P = 0.05 after applying Bonferroni correction, respectively.

Whole exome HiSeq sequencing of the G1 grandsire identified 61 mutations. All of the above phenotypes were linked by continuous variable mapping to a mutation in Nfkb1: T to A transversion at base pair 135,612,412 (v38) on chromosome 3, corresponding to base pair 79,571 in the GenBank genomic region NC_000069 within the donor splice site of intron 12. The strongest association was found with an additive model of inheritance to the total IgE phenotype (P = 5.979 x 10-8), wherein two affected variant homozygotes departed phenotypically from 10 homozygous reference mice and 11 heterozygous mice (Figure 4).

 

The effect of the mutation at the cDNA and protein levels has not been examined, but the mutation is predicted to result in skipping of the 139-nucleotide exon 12 (out of 25 total exons), resulting in a frame-shifted protein product beginning after amino acid 306 of the protein and premature termination after the inclusion of 80 aberrant amino acids.

 

          <--exon 11      <--exon 12 intron 12-->       exon 13-->      <--exon 15

78321 ……GTTCATAGACAG ……CCTGAAATCAAAG gtacctgggtggttta…… ACAAAGAGGAAG…… ……GCACCATAA…… 86746 
303   ……-V--H--R--Q- ……-P--E--I--K--                    -T--K--R--K-…… ……-A--P--*-
         correct        deleted                               aberrant

 

Genomic sequence and numbering corresponds to NC_000069. The donor splice site of intron 12, which is destroyed by the Roomba mutation, is indicated in blue lettering and the mutated nucleotide is indicated in red. 

Protein Prediction
Figure 5. The NF-κB and IκB families. The nuclear-κB family consists of five members: REL (c-Rel), RelA (p65), RelB, p105/p50 (NF-κB1), and p100/p52 (NF-κB2; see the record for xander).  They share a conserved N-terminal Rel-homology domain (RHD), which contains the dimerization, nuclear translocation, and DNA binding motifs. c-Rel, RelA, and RelB also have non-homologous C-terminal transactivation domains, and RelB contains an additional leucine zipper (shown in orange). These factors dimerized in various combinations to form NF-κB transcription factor complexes. The inhibitor of NF-κB (IκB) family contains the classical IκBs (IκBαIκBβ, and IκBε), the NF-κB precursors (p105 and p100), as well as B-cell lymphoma 3 (BCL-3), IκBζ, and IκBNS. These proteins are characterized by an ankyrin domain that contains five to seven ankyrin repeats and are able to bind to and inhibit the NF-κB RHDs. Exceptions are BCL-3 and IκBζ, which are able to bind p50 and p52 homodimers and induce transcription. Cleavage of p105 and p100 generates the p50 and p52 NF-κB, respectively. p105 also generates IκBγ (not shown).
Figure 6. Domain organization of NF-κB1. The p105 precursor and p50 are both shown. The protein has an N-terminal Rel homology domain (RHD), a glycine rich region (GRR), an ankyrin repeat domain (ARD), a death domain (DD), and a PEST motif. The location of the Roomba mutation is indicated in red. The image is interactive; click to view additional mutations in Nfkb1.

NF-κB1 (alternatively, p50/p105) is a member of the NF-κB protein family that are characterized by an N-terminal Rel homology domain (RHD), a glycine rich region (GRR), an ankyrin repeat domain (ARD), a death domain (DD), and a PEST motif [Figure 5 & 6; reviewed in (1)]. The p105 precursor protein can be proteolytically processed to generate p50 (i.e., amino acids 1-430 of p105). The RHD (amino acids 42-240, SMART) is comprised of the N-terminal domain, the dimerization domain (DimD), and a nuclear localization sequence that mediate DNA binding, nuclear localization, and subunit dimerization [reviewed in (1)]. The p50 RHD mediates co-translational dimerization with p105 and this dimerization is necessary for efficient p50 production (2;3). The GRR (amino acids 400-475 (4); 370-392, UniProt) is essential for the constitutive processing of p105 to p50 as well as for stabilization of the p50 subunit (2;5;6). Cohen et al. described a processing inhibitory domain (PID; aa 474-544) downstream of the GRR and upstream of the ARD that functions to regulate the constitutive processing of p105 (7). The ARD is at the C-terminus of p105 (amino acids 507-743, SMART) and has seven ankyrin motifs [reviewed in (1)]. The DD of p105 (aa 801-888, UniProt) is essential for IKK1 and IKK2-mediated phosphorylation of the p105 PEST motif by acting as a docking site for IKK (8;9). The PEST motif contains a conserved motif (Asp-Ser927-Gly-Val-Gly-Thr-Ser932) homologous to the IKK target sequence in IκBα [reviewed in (10)]. The Roomba mutation results in skipping of exon 12, followed by a frame-shifted protein after amino acid 306 and premature termination after the inclusion of 80 aberrant amino acids.

 

For more information about Nfkb1, please see the record for Finlay.

Putative Mechanism

NF-κB1 (p50 and p105) can form homodimers or heterodimers with c-Rel, RelA (p65), NF-κB2 (p52 and its precursor p100; see the record for xander), or RelB (11). The p105 precursor can act as an inhibitor of NF-κB dimers through both a direct dimerization to the NF-κB polypeptides as well as through interactions with preformed dimers (12). After agonist stimulation, p105 is degraded, facilitating the release of associated Rel subunits (i.e., RelA, c-Rel, and p50) and the translocation of the Rel subunits from the cytoplasm into the nucleus; RelB is not retained in the cytoplasm by p105 (13-16). In addition, p105 and IκBγ can associate with NF-κB dimers and prevent them from translocating to the nucleus (17). The p50 homodimer can bind to both nucleosomal DNA as well as naked DNA, facilitating the regulation of genes at sites of transcriptionally repressed chromatin as well as genes found in transcriptionally active chromatin (18). Depending on the cell type, the p50 homodimer can act as either a transcriptional activator or a repressor [reviewed in (10)]. The p50 homodimer typically binds DNA in unstimulated cells to repress NF-κB-dependent gene transcription (19). After stimulation, p50 homodimers can also function as transcriptional activators by an association of the homodimer with transcriptional co-activators.

 

 A variety of stimuli (e.g., cytokines, ultraviolet irradiation, and viral products) activate NF-κB complexes and the translocation of the activated complexes to the nucleus. In the nucleus, NF-κB acts as a transcription factor that regulates the expression of genes encoding a variety of immune response genes including pro-inflammatory cytokines (e.g., TNFα (see the record for PanR1), IL-1, and IL-6), chemokines [e.g., MIP-1α (macrophage inflammatory protein-1α) and RANTES (regulated upon activation, normal T-cell expressed and secreted)], cell adhesion molecules [e.g., E-selectin and VCAM-1 (vascular cell adhesion molecule-1)], effector molecules [e.g., defensins], enzymes [e.g., inducible nitric oxide synthase], and growth factors to regulate the recruitment of immune cells to the site of infection [(20;21); reviewed in (10)]. Inhibition of NF-κB leads to apoptosis [through the misregulation of anti-apoptotic proteins (e.g., c-IAP-1/2, AI, Bcl-2 and Bcl-XL)], delayed cell growth, reduced cell proliferation [through negative regulation of cell cycle regulator cyclin D1 (22)] and incorrect immune cell development [reviewed in (23-25)]. Please see the record for xander for additional details about NF-κB signaling.

  

T-cell mediated activation of B cells is required for extra-follicular and follicular responses to alum-precipitated proteins that are often used in vaccine formulations (26). Alum-precipitated OVA (alumOVA) stimulates follicular helper T (TFh) cells in germinal centers as well as the subsequent induction of B cells to differentiate into plasma cells, memory B cells, or centroblasts (26).  OVA-specific CD4+ T cells develop into Th2 cells that can subsequently induce extrafollicular plasmablasts. NF-κB1-deficient CD4+ T cells primed with alum-precipitated protein were unable to upregulate Th2-cytokines IL-4 and IL-13 (26).  In addition, Nfkb1-/- TFh cells have impaired CXCR5 expression, leading to reduced germinal center responses (26).  The loss of a T-dependent IgG response to rSFV-β-gal indicates that the Roomba mutation results in loss of functional p50/p105.

Primers PCR Primer
Roomba(F):5'- GTCTAAGTCTCATATAAGTTTGGCAGC -3'
Roomba(R):5'- CTGATGCTCACCGACACTAG -3'

Sequencing Primer
Roomba_seq(F):5'- CCTAACACTATGCAGCGT -3'
Roomba_seq(R):5'- CAAATGTCCTACACTAATGTTTGGG -3'
References

div>  22. Nakamura, Y., Grumont, R. J., and Gerondakis, S. (2002) NF-kappaB1 can Inhibit v-Abl-Induced Lymphoid Transformation by Functioning as a Negative Regulator of Cyclin D1 Expression. Mol Cell Biol22, 5563-5574.

Science Writers Anne Murray
AuthorsJin Huk Choi, Tao Yue, Xue Zhong, and Bruce Beutler
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