Phenotypic Mutation 'Schlendrian' (pdf version)
AlleleSchlendrian
Mutation Type missense
Chromosome7
Coordinate141,281,925 bp (GRCm39)
Base Change G ⇒ T (forward strand)
Gene Muc2
Gene Name mucin 2
Synonym(s) 2010015E03Rik
Chromosomal Location 141,276,583-141,308,428 bp (+) (GRCm39)
MGI Phenotype FUNCTION: [Summary is not available for the mouse gene. This summary is for the human ortholog.] This gene encodes a member of the mucin protein family. Mucins are high molecular weight glycoproteins produced by many epithelial tissues. The protein encoded by this gene is secreted and forms an insoluble mucous barrier that protects the gut lumen. The protein polymerizes into a gel of which 80% is composed of oligosaccharide side chains by weight. The protein features a central domain containing tandem repeats rich in threonine and proline that varies between 50 and 115 copies in different individuals. Downregulation of this gene has been observed in patients with Crohn disease and ulcerative colitis. [provided by RefSeq, Oct 2016]
PHENOTYPE: Homozygotes for a point mutation have soft feces at weaning and develop diarrhea associated with malapsorption syndrome. Homozygous null mutants pass blood in their feces at 6 months, and 65% of null mutants have intestinal tumors at 1 year. [provided by MGI curators]
Accession Number

NCBI RefSeq: NM_023566, MGI: 1339364

MappedYes 
Amino Acid Change Cysteine changed to Phenylalanine
Institutional SourceBeutler Lab
Gene Model not available
AlphaFold no structure available at present
SMART Domains Protein: ENSMUSP00000128250
Gene: ENSMUSG00000025515

DomainStartEndE-ValueType
Pfam:VWD 3 72 2.3e-14 PFAM
C8 107 181 1.82e-31 SMART
Predicted Effect probably benign
SMART Domains Protein: ENSMUSP00000136692
Gene: ENSMUSG00000025515

DomainStartEndE-ValueType
C8 11 85 1.61e-32 SMART
Blast:VWD 102 128 5e-8 BLAST
Predicted Effect probably benign
SMART Domains Protein: ENSMUSP00000141040
Gene: ENSMUSG00000025515
AA Change: C561F

DomainStartEndE-ValueType
low complexity region 5 18 N/A INTRINSIC
VWD 20 183 1.5e-40 SMART
C8 216 290 3.9e-15 SMART
Pfam:TIL 293 349 5.4e-10 PFAM
VWC 351 411 7e-4 SMART
VWD 378 542 8.8e-44 SMART
C8 579 653 1.2e-36 SMART
SCOP:d1coua_ 654 728 4e-8 SMART
VWC_def 820 865 1.3e-2 SMART
Predicted Effect probably damaging

PolyPhen 2 Score 1.000 (Sensitivity: 0.00; Specificity: 1.00)
(Using ENSMUST00000185406)
SMART Domains Protein: ENSMUSP00000140855
Gene: ENSMUSG00000025515

DomainStartEndE-ValueType
Pfam:VWD 3 73 5.6e-14 PFAM
C8 108 182 1.4e-35 SMART
Predicted Effect probably benign
Meta Mutation Damage Score Not available question?
Is this an essential gene? Probably nonessential (E-score: 0.099) question?
Phenotypic Category Autosomal Semidominant
Candidate Explorer Status loading ...
Single pedigree
Linkage Analysis Data
Penetrance 100% 
Alleles Listed at MGI

All alleles(7) : Targeted, knock-out(1) Targeted, other(2) Chemically induced(4)

Lab Alleles
AlleleSourceChrCoordTypePredicted EffectPPH Score
Eeyore APN 7 141693356 missense probably benign 0.35
kenny APN 7 nonsense
Winnie APN 7 141286029 missense probably damaging 1.00
IGL01303:Muc2 APN 7 141306132 missense probably benign
IGL01482:Muc2 APN 7 141307797 missense probably damaging 0.96
IGL01875:Muc2 APN 7 141306477 missense probably damaging 0.99
IGL02088:Muc2 APN 7 141305241 missense probably damaging 1.00
IGL02415:Muc2 APN 7 141305609 nonsense probably null
IGL02548:Muc2 APN 7 141305594 missense probably damaging 1.00
IGL02836:Muc2 APN 7 141300450 unclassified probably benign
IGL03196:Muc2 APN 7 141301367 missense probably damaging 0.97
Muskatenwein UTSW 7 141307176 missense unknown
nomoco UTSW 7 141307456 missense probably damaging 1.00
Seco UTSW 7 141284976 missense probably damaging 1.00
BB001:Muc2 UTSW 7 141281631 missense probably damaging 1.00
BB011:Muc2 UTSW 7 141281631 missense probably damaging 1.00
E0370:Muc2 UTSW 7 141282598 missense probably damaging 1.00
R0127:Muc2 UTSW 7 141302691 missense probably benign 0.00
R0179:Muc2 UTSW 7 141302708 missense probably damaging 1.00
R0201:Muc2 UTSW 7 141699185 frame shift probably null
R0299:Muc2 UTSW 7 141306466 missense probably damaging 1.00
R0547:Muc2 UTSW 7 141699185 frame shift probably null
R0699:Muc2 UTSW 7 141306037 missense probably damaging 1.00
R0900:Muc2 UTSW 7 141699185 frame shift probably null
R1348:Muc2 UTSW 7 141699185 frame shift probably null
R1466:Muc2 UTSW 7 141302711 missense probably damaging 1.00
R1466:Muc2 UTSW 7 141302711 missense probably damaging 1.00
R1625:Muc2 UTSW 7 141283405 missense probably damaging 1.00
R2010:Muc2 UTSW 7 141287444 missense probably damaging 0.99
R2149:Muc2 UTSW 7 141699185 frame shift probably null
R2163:Muc2 UTSW 7 141699185 frame shift probably null
R3008:Muc2 UTSW 7 141281347 missense possibly damaging 0.93
R3110:Muc2 UTSW 7 141299225 unclassified probably benign
R3112:Muc2 UTSW 7 141299225 unclassified probably benign
R3424:Muc2 UTSW 7 141279595 missense probably damaging 0.99
R3786:Muc2 UTSW 7 141283590 missense probably benign 0.01
R3854:Muc2 UTSW 7 141308081 missense probably damaging 1.00
R3964:Muc2 UTSW 7 141286233 missense probably benign 0.17
R3965:Muc2 UTSW 7 141286233 missense probably benign 0.17
R3966:Muc2 UTSW 7 141286233 missense probably benign 0.17
R3973:Muc2 UTSW 7 141300541 unclassified probably benign
R3974:Muc2 UTSW 7 141300541 unclassified probably benign
R3976:Muc2 UTSW 7 141300541 unclassified probably benign
R4327:Muc2 UTSW 7 141281577 missense probably damaging 0.96
R4694:Muc2 UTSW 7 141306082 missense probably damaging 1.00
R4764:Muc2 UTSW 7 141299345 missense possibly damaging 0.88
R4769:Muc2 UTSW 7 141286260 critical splice donor site probably null
R4798:Muc2 UTSW 7 141307877 missense probably benign 0.01
R4900:Muc2 UTSW 7 141303280 missense probably benign 0.32
R5383:Muc2 UTSW 7 141307456 missense probably damaging 1.00
R5489:Muc2 UTSW 7 141305169 missense probably benign 0.00
R5615:Muc2 UTSW 7 141277446 missense probably damaging 1.00
R5856:Muc2 UTSW 7 141299381 unclassified probably benign
R5919:Muc2 UTSW 7 141281171 missense probably damaging 0.97
R5953:Muc2 UTSW 7 141287951 missense probably damaging 0.96
R5979:Muc2 UTSW 7 141305143 missense probably damaging 0.99
R5979:Muc2 UTSW 7 141283493 splice site probably null
R6175:Muc2 UTSW 7 141282875 missense probably damaging 1.00
R6213:Muc2 UTSW 7 141305151 missense probably damaging 1.00
R6281:Muc2 UTSW 7 141306140 missense probably damaging 1.00
R6321:Muc2 UTSW 7 141287397 missense probably benign 0.28
R6390:Muc2 UTSW 7 141305883 missense probably damaging 0.97
R6485:Muc2 UTSW 7 141300473 unclassified probably benign
R6582:Muc2 UTSW 7 141282941 missense probably benign 0.00
R6683:Muc2 UTSW 7 141305214 missense probably benign 0.38
R6896:Muc2 UTSW 7 141306432 missense possibly damaging 0.48
R6906:Muc2 UTSW 7 141284976 missense probably damaging 1.00
R6924:Muc2 UTSW 7 141284077 missense possibly damaging 0.87
R7040:Muc2 UTSW 7 141305194 missense unknown
R7222:Muc2 UTSW 7 141290758 missense
R7251:Muc2 UTSW 7 141278965 missense possibly damaging 0.91
R7282:Muc2 UTSW 7 141306481 missense
R7315:Muc2 UTSW 7 141276645 missense probably damaging 0.99
R7421:Muc2 UTSW 7 141301863 missense
R7556:Muc2 UTSW 7 141307439 missense
R7651:Muc2 UTSW 7 141290750 missense
R7710:Muc2 UTSW 7 141287452 missense possibly damaging 0.92
R7776:Muc2 UTSW 7 141290942 missense
R7813:Muc2 UTSW 7 141282543 splice site probably null
R7843:Muc2 UTSW 7 141281662 missense probably benign 0.03
R7869:Muc2 UTSW 7 141303471 missense
R7924:Muc2 UTSW 7 141281631 missense probably damaging 1.00
R7993:Muc2 UTSW 7 141308173 missense
R8053:Muc2 UTSW 7 141284575 missense probably benign 0.01
R8068:Muc2 UTSW 7 141298422 missense
R8099:Muc2 UTSW 7 141299175 splice site probably null
R8192:Muc2 UTSW 7 141305215 missense
R8194:Muc2 UTSW 7 141290801 missense
R8545:Muc2 UTSW 7 141306130 missense unknown
R8701:Muc2 UTSW 7 141281850 missense probably damaging 1.00
R8883:Muc2 UTSW 7 141287469 missense probably damaging 0.98
R8894:Muc2 UTSW 7 141280758 missense probably damaging 1.00
R8905:Muc2 UTSW 7 141279643 missense probably benign 0.00
R9024:Muc2 UTSW 7 141287936 missense probably damaging 0.98
R9032:Muc2 UTSW 7 141287058 missense probably damaging 1.00
R9085:Muc2 UTSW 7 141287058 missense probably damaging 1.00
R9091:Muc2 UTSW 7 141290816 missense
R9104:Muc2 UTSW 7 141286224 missense probably damaging 1.00
R9114:Muc2 UTSW 7 141287983 nonsense probably null
R9270:Muc2 UTSW 7 141290816 missense
R9297:Muc2 UTSW 7 141302759 missense
R9325:Muc2 UTSW 7 141298559 missense
R9354:Muc2 UTSW 7 141307157 missense
R9386:Muc2 UTSW 7 141279389 missense probably damaging 1.00
R9529:Muc2 UTSW 7 141287453 missense possibly damaging 0.55
R9550:Muc2 UTSW 7 141308242 missense probably damaging 1.00
R9583:Muc2 UTSW 7 141300559 missense
R9607:Muc2 UTSW 7 141305190 missense
R9646:Muc2 UTSW 7 141276643 missense probably benign
R9651:Muc2 UTSW 7 141288014 missense probably damaging 0.99
R9774:Muc2 UTSW 7 141285811 missense probably benign
R9784:Muc2 UTSW 7 141280785 nonsense probably null
Z1176:Muc2 UTSW 7 141300451 missense
Z1177:Muc2 UTSW 7 141298531 missense
Mode of Inheritance Autosomal Semidominant
Local Stock Live Mice, Sperm, gDNA
MMRRC Submission 031706-UCD
Last Updated 2017-09-13 3:34 PM by Diantha La Vine
Record Created unknown
Record Posted 2009-07-01
Phenotypic Description
Figure 1. Increased susceptibility to DSS-induced colitis in Schlendrian mice. Percent initial weight was examined on the indicated days after administration of 1% DSS. Schlendrian mice exhibited increased weight loss relative to wild type mice beginning 5 days after initiation of DSS treatment.
The semidominant Schlendrian phenotype was identified among ENU-mutagenized G3 mice in a screen for mutants with susceptibility to dextran sulfate sodium (DSS)-induced colitis (DSS-induced Colitis Screen).  When challenged with a low dose of DSS in their drinking water (1%), Schlendrian homozygotes exhibit increased weight loss relative to wild type mice five days after initiation of treatment.  Both Schlendrian homozygous and heterozygous mice were treated with 1% DSS, and weight loss was compared to wild type mice (Figure 1). Two of these mice died on day 7 of treatment.  
Nature of Mutation

The Schlendrian mutation was mapped to Chromosome 7 by outcrossing to C3H/HeN mice, and crossing the F1 hybrids to the C3H/HeN strain (as a dominant phenotype), and corresponds to a G to T transversion at position 1689 of the Muc2 transcript in exon 13 of 47 total exons (1)

 
 
1673 AAGGCCCAATCAAGCTGCCACGACAAGCTGGAC
556  -K--A--Q--S--S--C--H--D--K--L--D-
 
The mutated nucleotide is indicated in red lettering, and causes a cysteine to phenylalanine change at amino acid 561 of the MUC2 protein.
Illustration of Mutations in
Gene & Protein
Protein Prediction
Figure 2.  Domain structure of Mucin2. The Schlendrian mutation (red) causes a cysteine to phenylalanine change in the D2 domain of the MUC2 protein. S=Signal sequence; D=D domains (homology to VWF mediates trimerization); CR=Cystein-rich domain; TR= Tandem repeat domain (heavily O glycosylated); GDPH=GDPH autocatalytic proteolytic site; B=B domain (homology to VWF); C= C domain (homology to VWF); CK= Cysteine-knot domain (homology to VWF mediates dimerization). This image is interactive. Click on the image to view other mutations found in Mucin2 (red). Click on the mutations for more specific information.
The Muc2 gene encodes a secreted member of the mucin family of proteins, which are characterized by their large mass, complex biochemical composition (they are highly glycosylated), an extensive number of variable tandem repeats, and tendency to form higher-order structures through polymerization. Some mucins are integral membrane proteins (2;3)
 
The structural feature that is common to all mucins is the tandem-repeat domain, which contains tandem repeats of identical or highly similar sequences that are rich in serine, threonine and proline residues. The specific sequence and number of tandem repeats is highly variable among different mucins and among orthologous mucins from different species (2;3). These domains are O-glycosylated on the serine and threonine residues by the addition of N-acetylgalactosamine (GalNAc). Each O-glycan is then elongated by adding various hexoses such as galactose, N-acetylglucosamine (GlcNAc), fucose, sialic acid, and N-acetylneuraminic acid (3). The composition of mucin oligosaccharides is highly variable, tissue-dependent, and can confer negative charges or hydrophobicity depending on the moiety used or on post-translational modification such as sulfation (2-4)
 
MUC2 contains two tandem repeat domains that are located in the middle of the protein (Figure 2), and shows extensive polymorphism due to the variable number of tandem repeats that can be present (5-9). For human MUC2, the first tandem repeat domain is invariant and consists of 21 repeats of a 23 amino acid sequence, while the second domain contains between 51-115 repeats of a 16 amino acid sequence (5;10). Thus, the size of the MUC2 protein varies widely between individuals and ethnicities with the most common allelic form containing over 5100 amino acids (6). In mouse, the central repetitive region of MUC2 contains two distinct repetitive regions consisting of 8 and 10 amino acid tandem repeats, respectively (1). The characteristics of the tandem-repeat domains of mucins determine the extent of mucin glycosylation, size, and biochemical characteristics. MUC2, for instance, has a rigid structure and is considered to be insoluble (11).  
 
Unlike the tandem repeat domains, the other domains typically present in mucins tend to be highly conserved (1;7;12). The majority of these motifs in MUC2 are cysteine-rich (Figure 2), and many have high homology with von Willebrand platelet aggregating factor (VWF) (13). These include the five D domains known as D1, D2, D’, D3 and D4, as well as the B, C and cysteine-knot (CK) domains. The D1-D3 domains are located in the N-terminus of the protein, and the D4, B, C and CK domains are located in the C-terminus. The D’ domain is not always considered to be a separate domain, and the B domain is sometimes labeled as C1 (2;3;9). The CK domain is also conserved with a motif found in TGF-β and mediates the dimerization of mucin molecules through disulfide bond formation (14;15). Similarly, the N-terminal D-domains mediate mucin trimerization through disulfide bond formation between cysteines present in the D3 domains (16). The B and C domains of mucins have been shown to associate with trefoil factors (TFF), which play important roles in mucus formation and integrity (17-19). MUC2 also contains two cysteine-rich regions located before and after the first tandem repeat.     
 
In addition to disulfide bonds, MUC2 polymers are held together by other intermolecular bonds, although the nature of these remains unclear (11). Located near the N-terminus of the D4 domain is a GDPH autocatalytic cleavage site with cleavage occurring between the D and P residues.  The reaction is not enzyme-mediated and occurs at the low pH of the late secretory pathway (20). It has been suggested that this cleavage leads to the formation of a unique covalent bond between the carboxy-terminal D residue of one MUC2 subunit and an oligosaccharide side chain present on another subunit. 
 
Collagen and heparin binding sites are also present in the MUC2 sequence. The heparin site is near the C-terminal end and consists of clusters of basic residues. In addition, MUC2 contains multiple potential N-glycosylation sites (6). At the very N-terminus is a signal sequence motif.
 
The Schlendrian mutation alters a conserved cysteine residue located in the second VWFD domain (Figure 2). Expression and localization of the altered protein is being examined. 
Expression/Localization
Using real-time RT-PCR, human MUC2 was found to be highly expressed in adult small intestine and colon. Expression was lower in fetal lung and adult trachea and stomach, with weak expression in skeletal muscle, testis, and prostate. No expression was detected in other tissues examined (21). These results were similar to studies localizing MUC2 mRNA expression primarily to the intestine, with some expression in the airways and the gallbladder (22;23). MUC2 gene expression in the intestine is initiated early during embryonic development (24). MUC2 protein is highly expressed in the intestinal mucus layers, and localizes to the secretory vesicles of intestinal goblet cells (25;26). Very low levels of MUC2 are present in bronchial mucus (27;28). The expression of Muc2 mRNA and protein in rodents and other mammals is similar to humans (7;12;26).
 

Many epithelial-based tumors from multiple tissues express increased levels of MUC2 (29;30).

Background
Mucins are expressed by many epithelial tissues that exist in relatively harsh environments including the stomach, intestinal tract, respiratory tract, cervix and specialized organs such as the liver, pancreas, gall bladder, kidney, mammary gland, salivary gland, lacrimal gland and eye. The layer of mucus produced by these epithelial tissues provides a protective barrier against fluctuations in molecular composition, pH, ionic concentration, pathogens, and toxins. Mucins, with their high molecular weight and complex glycosylation, are major components of epithelial mucus and have a central role in maintaining homeostasis and promoting cell survival under variable conditions. Furthermore, the specific molecular composition and higher-order structures of various mucins contribute to the specialized functions of the different epithelial tissues (2;3). For instance, colonic mucins are reported to be strongly negatively charged due to sialic acid moieties and sulfation and their carbohydrate chains display a characteristic structure, while mucins from colon cancer cell lines display short carbohydrate side chains (31). Mucus gels have been shown to contribute to the immune defense by sequestering multiple cytokines including TNF-α that mediate critical inflammatory responses (2). The immunoglobin (Ig)A antibody is secreted into mucus layers of many epithelial tissues where it provides important antimicrobial activity against pathogens (32). The IgG Fc-binding protein, FcgammaBP, is also localized to the mucus layers of many epithelial tissues, and likely plays a role in immune defense (33). Other bioactive molecules found in mucus layers include trefoil factors (18), epithelial growth factor (EGF), and TGF-α (2).
 
Figure 3. A, Goblet cells are located in the glandular epithelium of the intestinal mucosa and release mucin from its apical surface in response to cholinergic stimulation. MUC2 is the major molecular component of the inner and outer mucosal layers of the intestinal tract. The inner layer is denser and devoid of bacteria, while the outer layer is looser and is colonized by commensal bacteria. B, Before being secreted, MUC2 is assembled in the endoplasmic reticulum (ER) with dimerization and N-glycosylation. MUC2 is then transferred to the Golgi where it is O-glycosylated. Oligomerization occurs late in the secretory pathway and may occur concomitantly with secretion. MUC2 is stored in secretory granules of intestinal goblet cells until released.
MUC2 is the major molecular component of the inner and outer mucosal layers of the intestinal tract (34). The mammalian intestinal mucosa undergoes constant and rapid renewal throughout life. Intestinal epithelial cells begintheir existence as the daughter cells of a minority stem cell population located approximately four cell positions from the base of the intestinal crypts. These cells differentiate into enterocytes,Paneth cells, enteroendocrine cells, and the mucus-producing goblet cells. The mucosal and epithelial layers of the intestinal tract aid in absorption of food and water, protect against intestinal pathogens (35), and prevent an inappropriate immune response against commensal bacteria (36). In intestinal goblet cells, MUC2 assembly begins in the endoplasmic reticulum (ER) with dimerization of MUC2 subunits and N-glycosylation (14). Subsequently, MUC2 is transferred to the Golgi where it is O-glycosylated (see Protein Prediction)(FIgure 3). Further oligomerization appears to occur late in the secretory pathway and may occur concomitantly with secretion (16). MUC2 is stored in secretory granules in intestinal goblet cells and rapidly released at the apical surface in response to mucin secretagogues such as cholinergic stimulation (37). Unregulated MUC2 secretion also occurs and depends upon continuous transport of mucin granules from Golgi vesicles to the cell surface (38). Although both intestinal mucus layers contain mucin as the primary component, the inner layer is denser and devoid of bacteria. The outer layer is looser, has an expanded volume due to MUC2 proteolytic cleavages, and is colonized by commensal bacteria (34).
 
Because the intestinal mucosal layer plays a critical role in immune defense and protection against commensal bacteria, the disruption of the intestinal mucus layer and epithelium can result in intestinal bowel disease (IBD; OMIM #266600). IBD is a chronically recurring inflammatory disorder of the intestine, and results from excessive and sustained inflammatory host immune responses against antigens of commensal intestinal microbes. The clinical appearance of IBD is heterogeneous, and can include diarrhea, abdominal pain, rectal bleeding, fever, weight loss, and signs of malnutrition. Crohn’s disease (CD) and ulcerative colitis (UC) are the two major forms of IBD. Crohn’s disease can affect any part of the gastrointestinal tract, most frequently the terminal ileum and colon. In contrast, UC exclusively affects the mucosal lining of the colon and rectum (36). MUC2 polymorphisms are associated with the development of CD (21). Moreover, IBD patients often show alterations in mucin composition, including decreases in MUC2 expression, abnormal expression of other mucins, as well as differences in the glycosylation and sulfation of MUC2 (18;21;39;40). The excessive inflammation that occurs in IBD may lead to upregulation of MUC2 as MUC2 is regulated in vitro by a variety of inflammatory mediators including NF-κB, an important effector of the immune system (3;21)
 
Although not a major component of bronchial mucus (27;28), MUC2 may also play a role in the development of chest diseases such as cystic fibrosis (CF; OMIM #219700), and asthma (OMIM #600807) as upregulation of MUC2 gene transcription occurs in these diseases (41;42).  However, the presence of MUC2 protein remains very low in the bronchial secretions of patients with disease (27;28), although this could be due to the insolubility of the MUC2 glycosylated protein.   
 
Targeted inactivation of the murine Muc2 gene resulted in the spontaneous development of intestinal tumors (43), and on certain genetic backgrounds, the development of chronic inflammation and colitis (44). In humans, inflammation due to chronic ulcerative colitis is correlated with a significantly increased incidence of colon tumors (2)Muc2-/- mice lacked morphologically distinguishable goblet cells, although the goblet cell lineage remained intact. Muc2 knockout mice also exhibited increased proliferation, decreased apoptosis and increased migration of epithelial cells along the intestinal crypts. Two missense mutations in murine Muc2 also resulted in the development of ulcerative colitis in mice, although the mechanism behind the development of disease in these animals appears to be somewhat different than complete lack of the protective mucus layer (26) (see Putative Mechanism). In addition, mice lacking the enzyme responsible for appropriately glycosylating MUC2, and mice lacking an enzyme catalyzing the formation of MUC2 disulfide bonds lacked MUC2 protein and were susceptible to DSS-induced colitis (45;46).
 
The role of MUC2 as a potential tumor suppressor contrasts with the high expression of MUC2 in many epithelial cancers (29). Subsequent studies suggest that the expression of MUC2 in certain cancers is associated with a lack of invasiveness (30). Furthermore, MUC2 expression is decreased in some types of colon cancer (31).
Putative Mechanism
The Schlendrian mutation alters a cysteine in the N-terminal D2 domain of MUC2. The susceptibility of Schlendrian mutant mice to low doses of DSS-induced colitis suggests that this residue may affect MUC2 biosynthesis and assembly, perhaps by disrupting the formation of an important disulfide bond. MUC2 trimerization does occur through disulfide bond formation in the D3 domain of MUC2 (16), but a similar role for D2 has not been demonstrated. 
 
In mice with missense mutations in Muc2, the development of colitis resulted from the aberrant oligomerization and subsequent accumulation of MUC2 in the ER, which lead to ER stress, triggering of the unfolded protein response (UPR), subsequent inflammation and goblet cell apoptosis (26). These mutations resulted in amino acid changes in either the MUC2 D3 domain or the C-terminal D4 domain, further demonstrating the importance of the D domains in MUC2 function and assembly. Several recent reports provide evidence for a causal role for ER stress in IBD. Mice lacking IRE1β, an ER stress sensor expressed in intestinal epithelial cells, are more susceptible to DSS-induced colitis relative to wild type mice (47).  These mice exhibit increased levels of the ER chaperone GRP78 in the colonic mucosa, indicative of ER stress.  Mice lacking XBP1, a UPR response protein activated by IRE1, in intestinal epithelial cells display a loss of secretory Paneth cells and goblet cells in the intestinal epithelia, as well as spontaneous inflammation in the ileum (48). Elevated levels of GRP78 and CHOP, and IRE1 hyperactivation in the small intestine were also detected in these mice.  In addition, single nucleotide polymorphisms (SNPs) in the XBP1 locus have been correlated with IBD in humans (48). Finally, mice with a missense mutation in Mbtps1 encoding the Site I protease (S1P), also demonstrate increased susceptibility to DSS-induced colitis (49) (see the record for woodrat). In response to ER stress, S1P cleaves the ATF6 transcription factor, which then activates transcription of UPR target genes such as XBP1 and GRP78 (50).
 
We have not demonstrated that the Schlendrian mutation results in MUC2 accumulation in the ER. It is also possible that the Schlendrian mutation results in complete lack of MUC2 protein, which can also result in the development of colitis (44). However, unlike Muc2-/- mice, the Schlendrian mutation is semidominant, suggesting the presence of aberrant protein. It is also possible that secretion of MUC2 in Schlendrian animals will result in alterations of the intestinal mucus layer. Changes in mucus formation may result in inability to bind to molecules such as trefoil factors or sequester important bioactive molecules. Mice with defects in TFF3, TGF-α and the EGF receptor (see the record for Velvet) all develop severe colitis after exposure to DSS (17;51;52).
Primers Primers cannot be located by automatic search.
Genotyping
Schlendrian 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
Schlen(F): 5’- TCCTGAACTGCTGCCAGTCAAC -3’
Schlen(R): 5’- TGGACCAGGCTCCCTTTCACAAAC -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
Schlen_seq(F): 5’- CTCTGTGGAAACTTCAATGGC -3’
Schlen_seq(R): 5’- TGTCCTTGACAAGCCAGTG -3’
 
The following sequence of 1107 nucleotides (from Genbank genomic region NC_000073 for linear DNA sequence of Muc2) is amplified:
 

 
			4800                                                                 t
4801 cctgaactgc tgccagtcaa cagagccagc tgagattcgg acagcctaag agtctgggca
4861 aggagaggcc ttgtgtcctc aggcagactc tattcttggg tccctgctag tggaaggggg
4921 tggtgggcat gtcaccccat agtatggtgg aaccaaggag ccctgcagcc tttcaccatg
4981 tccttccttg tcttatagcc agcttctcca tcttccaacc ctcctcctac cacattgttg
5041 tgaacacgaa gttcgggctg cggctgcaga tccagttgct tccagtcatg cagctttttg
5101 tgactctgga ccaggctgcc cagggacagg tgcagggtga gtggctctct cctgtcttgt
5161 ctctgaaaaa tccccatgag ggtcctattt ttttccccca cccccaggtt cttcctaatc
5221 ctgtcctggc cctttaggtc tctgtggaaa cttcaatggc ctagagagtg atgacttcat
5281 gacgtctggt ggaatggtgg aggccaccgg tgctggcttc gccaatacct ggaaggccca
5341 atcaagctgc cacgacaagc tggactggct agatgacccc tgctccctca acattgagag
5401 tggtaaggct caggagaagc tggttgctgt ccactggctt gtcaaggaca cacaatcctg
5461 acagtccagc ctcagagcag atggggctcc tgatgaagac ataggatgtg ggtgaggagt
5521 gggtgtaggt cacatggcct atggtgctgg gatcagcaca tttacctgct gtttcagttg
5581 acagtggccc catggtggca gcattccagg tgacaaagta aatggactgg gcaggctaac
5641 tgctgggtgg tggctctcat ctcggcctgg cttaatgcta ggatgacatg cccttctatc
5701 catttctcca tcatatctgt ggatttctag ccccttgggg tcgaaaaagg gagaggtggg
5761 tgttatgcag aaaggtctca tcttgttcat agctgcctgg agttatgaag aaaggggtct
5821 ggctttggtc acccaggaga ccatgtcacc tccatcctgg gtgatcagac tttaggctca
5881 gggtttgtga aagggagcct ggtcca 
			PCR primer binding sites are underlined; sequencing primer binding sites are highlighted in gray; the mutated G is shown in red text.
References
Science Writers Nora G. Smart
Illustrators Diantha La Vine
AuthorsKatharina Brandl, Bruce Beutler
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