Genetic regulation of MUC1 alternative splicing in human tissues.

Abstract

The membrane mucin MUC1 is aberrantly expressed in a variety of cancers, and in stomach, it is a ligand for Helicobacter pylori where it plays a role in gastric carcinogenesis. Splicing variation, leading to a 9-amino acid insertion in the signal peptide region, was proposed to be because of a single-nucleotide polymorphism (rs4072037) at the 5' end of exon 2, but is also reported to be cancer-associated. However, the effect of rs4072037 on this splicing event in healthy non-cancer tissues and on the additional spliceoforms ofMUC1, including those lacking the polymorphic tandem repeat (TR) domain, has never been investigated. Here we show that in both foetal and adult tissues of known genotype, there is clear evidence for the role of rs4072037 in controlling alternative splicing of the 5' exon 2 region of both full-length transcripts and those lacking the TR domain. Although there is some evidence for additional genetic and epigenetic influences, there is no indication of an effect of the TR domain on the proportions of the spliceoforms. In conclusion, over-representation of certain transcripts in tumour material cannot be evaluated without information on the SNP genotype as well.

Full text

Page 1

Genetic regulation of MUC1 alternative splicing in human tissues
W Ng1,3, AXW Loh1,4, AS Teixeira1,5, SP Pereira2and DM Swallow*,1
1Research Department of Genetics, Evolution and Environment, University College London, Wolfson House, 4 Stephenson Way, London NW1 2HE, UK;
2Division of Medicine, Institute of Hepatology, Royal Free & University College London Medical School, London, UK;3University Department of Paediatrics,
John Radcliffe Hospital, Oxford, UK
The membrane mucin MUC1 is aberrantly expressed in a variety of cancers, and in stomach, it is a ligand for Helicobacter pylori where
it plays a role in gastric carcinogenesis. Splicing variation, leading to a 9-amino acid insertion in the signal peptide region, was proposed
to be because of a single-nucleotide polymorphism (rs4072037) at the 50end of exon 2, but is also reported to be cancer-associated.
However, the effect of rs4072037 on this splicing event in healthy non-cancer tissues and on the additional spliceoforms of MUC1,
including those lacking the polymorphic tandem repeat (TR) domain, has never been investigated. Here we show that in both foetal
and adult tissues of known genotype, there is clear evidence for the role of rs4072037 in controlling alternative splicing of the 50exon
2 region of both full-length transcripts and those lacking the TR domain. Although there is some evidence for additional genetic and
epigenetic influences, there is no indication of an effect of the TR domain on the proportions of the spliceoforms. In conclusion, over-
representation of certain transcripts in tumour material cannot be evaluated without information on the SNP genotype as well.
British Journal of Cancer (2008) 99, 978–985. doi:10.1038/sj.bjc.6604617
Published online 26 August 2008
& 2008 Cancer Research UK
www.bjcancer.com
Keywords: MUC1; splicing; polymorphism; transcript; gene regulation
? ???????????????????????????????????????????
MUC1 is a highly polymorphic membrane-associated mucin that is
often aberrantly expressed in cancer (Taylor-Papadimitriou et al,
2002). It has a centrally located tandem repeat (TR) domain (Lan
et al, 1985; Gendler et al, 1987, 1988, 1990; Swallow et al, 1987;
Hareuveni et al, 1990) comprised of 20–120 or more repeat units
of 60 nucleotides, which encode 20 amino acids. The repeating
units include several serine and threonine residues, which carry
most of the glycosylation, and this glycosylation, as well as
the general pattern of expression, is altered in cancerous cells
(Taylor-Papadimitriou et al, 2002). Susceptibility to Helicobacter
pylori gastritis and to gastric cancer appears to be associated with
MUC1 allele length (Carvalho et al, 1997; Silva et al, 2001, 2003;
Vinall et al, 2002). MUC1 binds to H. pylori (Linden et al, 2004;
McGuckin et al, 2007), Muc1 knockout mice are susceptible to
H. pylori gastritis (McGuckin et al, 2007) and there is an altered
pattern of expression of MUC1 in H. pylori gastritis (Vinall et al,
2002). The observations that MUC1 plays a role in the progression
to gastric cancer highlight the importance of understanding all the
aspects of the normal variation of this gene.
During the course of various cancer-related studies, several
variant MUC1 transcripts were reported. Early cloning experi-
ments revealed the presence of transcripts (a and b) with an
alternative 27bp intron retention event at the start of exon 2
(Ligtenberg et al, 1990). Although a genetic basis for this
variable splicing event was first suggested by Ligtenberg et al
(1991), who used cancer cell lines, the longer a transcript was
also reported to be more abundant in cancer tissues (Weiss et al,
1996; Obermair et al, 2001, 2002; Schmid et al, 2002, 2003) and to
have potential prognostic value. Therefore, the function of the
genetic polymorphism implicated (rs4072037 G/A, located at
nucleotide position 8 of exon 2 of the b variant) was left in some
doubt. An additional alternative splicing event is known to occur
at the 50end of exon 2, which generates two minor transcripts
denoted as c and d, and was first reported by Obermair et al
(2001). Variants c and d, respectively, have 9 and 27 fewer
nucleotides, at the start of exon 2, than the b transcript. The splice
variants observed in breast (Schmid et al, 2002, 2003), cervical
(Obermair et al, 2001) and ovarian tumours (Obermair et al, 2002)
were suggested to be associated with transcripts b and a, respec-
tively, and thus are possibly also under the influence of rs4072037.
These alternative splicing events lie within the signal peptide
domain and are very close to two signal peptide cleavage sites that
have been observed experimentally in b variant (Parry et al, 2001).
MUC1 is also known to have alternative spliceoforms that lack
the TR domain (Zrihan-Licht et al, 1994a,b; Baruch et al, 1997,
1999; Obermair et al, 2001, 2002). Each of these transcripts is
generated through the use of one additional 50splice site and one
of three different 30splice sites in the sequence, which flank the TR
domain in exon 2. MUC1/Z is the longest transcript, followed by
MUC1/Y, which is 54 bases shorter, followed by MUC1/X, which is
a further 19 bases shorter, using the nomenclature adopted by
Obermair et al (2002). The three transcripts and an additional
form called MUC1/Y alt, some of which are likely to be functional
(Levitin et al, 2005), have been detected in breast tumours (Baruch
et al, 1997, 1999; Hartman et al, 1999; Obermair et al, 2001),
Received 30 May 2008; revised 24 July 2008; accepted 28 July 2008;
published online 26 August 2008
*Correspondence: Dr DM Swallow; E-mail: d.swallow@ucl.ac.uk
4Current addresses: School of Biological Sciences, Nanyang Technological
University, 60 Nanyang Drive, Singapore 637551, Republic of Singapore
5Current addresses: Molecular and Population Genetics Laboratory,
Cancer Research UK – London Research Institute, 44 Lincoln’s Inn Fields,
London WC2A 3PX, UK
British Journal of Cancer (2008) 99, 978–985
& 2008 Cancer Research UKAll rights reserved 0007– 0920/08$32.00
www.bjcancer.com
Genetics and Genomics

Page 2

cervical tumours (Obermair et al, 2001) and ovarian tumours
(Obermair et al, 2002).
The aim of this study was to investigate the role of rs4072037 in
relation to the alternative splicing events of MUC1, in both TR-
containing and TR-negative transcripts, for a range of normal non-
cancer tissues, to help evaluate published results and as a platform
for future cancer studies. Foetal samples were used to obtain
several tissues from a single individual as well as the same tissue
from many individuals. In addition, a number of adult gastric and
duodenal samples and cancer cell lines were examined. As the TR
domain makes up a significant proportion of the transcript for
MUC1 and is known to show considerable length variation in
different individuals, this might affect the rate of transcript
synthesis or transcript stability. The TR lengths of MUC1 were
therefore examined in the same set of foetal samples.
MATERIALS AND METHODS
Samples
Foetal tissues were obtained from the MRC Tissue Bank and from
the adult tissues from patients undergoing clinically indicated
gastroscopy at University College London Hospitals NHS Founda-
tion Trust (Joint UCL/UCLH Committees on the Ethics of Human
Research approvals 04/0011 and 01/0237). Genomic DNA and RNA
from nine cancer cell lines were also tested: lung cancer cell lines
A427, A549, NCI-H522, NCI-H358, NCI-H441, NCI-H23, NCI-
H460, laryngeal carcinoma and HEP-2, and were kindly supplied
by Dr Jeremy Hull, University Department of Paediatrics, John
Radcliffe Hospital, Oxford.
RNA preparation
Tissues were stored at ?701C. Frozen tissue (25–50mg) was
crushed into a fine powder with a pestle and mortar, followed by
RNA extraction using RNA-Beet Biogenesis Ltd, Poole, UK,
according to the manufacturer’s protocol. The total RNA was
re-suspended in RNase-free water, quantified using a spectro-
photometer and the quality checked on 1% agarose gels.
Southern blot analyses were performed as previously described
(Fowler et al, 2003).
DNA preparation
For PCR-based genotyping, genomic DNA was retrieved from the
residue and organic phase of the RNA extraction mixture, after
removal of the aqueous phase, by adding a back extraction buffer
(4 M guanidine thiocyanate, 50mM Na citrate, 1 M Tris, pH 10.5),
followed by DNA precipitation using isopropanol, as described in
the manufacturer’s instructions. Higher quality tissue DNA, used
for Southern blotting, was prepared using the PuregenesDNA
Purification Kit (Gentra Systems, Minneapolis, MN, USA): 10–
20mg tissue was crushed in liquid nitrogen with a pestle and
mortar and the DNA extracted according to the manufacturer’s
instructions.
cDNA synthesis
Complementary DNA was synthesised with M-MLV Reverse
Transcriptase (Invitrogen, Paisley, Scotland) using 200 or 400ng
of total RNA, 0.2mM of each dNTP, 0.25mg random hexamers and
20U of RNAase inhibitor (RNaseOUTt, Invitrogen) in 20ml. For
PCRs, a 1/10 dilution of the cDNA was used. In each case, control
transcriptions were run with no reverse transcriptase; no-template
blanks were also included in the PCRs as negative controls.
Primers from a non-polymorphic region of MUC1 and from the
ribosomal S14 gene (RPS14) were used as controls for template
quality.
Oligonucleotide primers were purchased from Sigma-Genosys,
Haverhill, UK. Thermocycling was conducted on an MJ Research
PTC-200 Peltier Thermal Cycler (Genetic Research Instrumentation,
Braintree, UK). Primer sequences and cycling conditions are shown in
Supplementary Table 1.
For rs4072037 typing, the primers 1946 AGS and Cy5-labelled
Exon2AS (see Supplementary Table 1) were used to generate a
260bp product, followed by restriction enzyme digestion using
AlwN1, for which the sequence cuts when there is an A allele and
fails to cut if there is a G allele, as was done earlier (Fowler et al,
2003). Samples with no uncut product were interpreted as AA and
no cut product, as GG, assuming no silent alleles.
Electrophoresis was conducted on 4.8% acrylamide (19:1)
UltraPuret Sequagel gels using an ALF expresst sequencer
(Amersham Pharmacia, Little Chalfont, UK). PCR products were
run with molecular size markers mixed with the PCR product and
loading buffer. The same technique was used for transcript
analyses. The relative peak heights were also recorded to semi-
quantify the relative amount of a and b transcripts.
PHASE (version 2.1), which uses a Bayesian statistical method
for haplotype construction (Stephens et al, 2001), was downloaded
from http://stephenslab.uchicago.edu/software.html.
RESULTS
Relationship of splicing with genotype: variable exon 2
spliceoforms
All the samples were first typed for rs4072037. Corresponding cDNA
from 68 foetuses (total of 120 tissue samples), 36 adults (21 gastric
and 15 duodenal samples of which 13 and 9, respectively, had normal
histology and the rest had various degrees of inflammation) as well
as the nine cancer cell lines were amplified using primers to detect
the variable splicing at the 50end of exon 2 (Figure 1A).
Up to four possible transcripts, a, b, c and d, could be detected
in a single sample. Figure 1B shows PCR products from three
representative individuals of AA, AG and GG genotypes. The
results are summarised in Table 1.
There was a clear correlation between the transcripts observed
and the rs4072037 genotype. In all cases where the rs4072037 G
allele was present, a transcripts were present in the RNA, and when
the rs4072037 A allele was present, there were b transcripts. In the
AA homozygotes, there was no a transcript, and in most GG
homozygotes, there was no b transcript, although in two GG foetal
lungs and one GG foetal stomach, one GG adult stomach and one
GG adult duodenum, a trace amount of the b variant was detected.
In the AG heterozygotes, both b and a transcripts were observed,
though b was usually more prominent and the proportions of a
and b were variable (Figure 1C).
Expression of the two minor transcripts, c and d, was also
associated with the rs4072037 allele. When detected, the smallest
transcript d was always associated with G allele, which also
produces the a transcript. The c transcript on the other hand was
found with the A allele, which also generates the b transcript.
Spliceoforms lacking the TR domain
The expression of the ‘non-TR’ transcripts was examined using the
foetal tissues and with the same protocol with the same exon 1
primer and a reverse primer located at the 30end of exon 2
(Figure 1), except that two extra rounds of PCR amplification and
double the cDNA concentration were usually required to detect
these components. Up to seven different transcripts were detected
(Figure 2). A summary of the results is shown in Table 2. On
the basis of their sizes, the non-TR transcripts were identified as
the previously reported MUC1/X, MUC1/Y, MUC1/Z, as well as
MUC1/Y alt (Obermair et al, 2001), the non-TR transcript
MUC1 alternative splicing in human tissues
W Ng et al
979
British Journal of Cancer (2008) 99(6), 978–985
& 2008 Cancer Research UK
Genetics and Genomics

Page 3

analogous to a. Two additional components were 27 bases larger
than MUC1/X and MUC1/Z, respectively, and thus are expected to
be alt or a-like variants of transcripts X and Z, respectively, and
were thus named MUC1/X alt and MUC1/Z alt. MUC1Yc was so
named because it is 9 bases shorter than the MUC1/Y variant and
thus likely to correspond to a non-TR version of c.
A clear genotype-associated pattern of expression for these
variants was observed (Table 2). In rs40723037 AA homozygotes,
only the non-alt variants were present, whereas in rs40723037 GG
homozygotes, only the alt variants were observed. In the AG
heterozygotes, both the alt and non-alt forms were detected.
Variability of proportions of the major transcripts a and b
The fact that in the rs4072037 heterozygotes, the peak heights of
the a transcript were almost always lower than the b transcript
(Figure 1B and C) is probably partly a reflection of the relative
signal detection by the ALF Expresst machine and may also reflect
the PCR of the different sized fragments (a being 27 nucleotides
longer than b). However, the relative levels of the two transcripts
(Figure 1C), though variable, were reproducible for a particular
sample. Although measurements using the ALF Express could at
best be considered semi-quantitative, peak heights were recorded
to evaluate this variability in relation to tissue source and
individual.
Tissue differences
Consideration of all heterozygous samples of a particular tissue
showed that the a/b ratios were not normally distributed,
particularly in the case of the liver and trachea. The median
values obtained for each of the tissues were 0.47 (range 0.06–0.82)
for lung, 0.49 (range 0.12–0.64) for stomach, 0.7 (range 0.08–1.33)
for liver and 0.26 (range 0.04–0.35) for trachea, and the data sets
were compared using the non-parametric Mann–Whitney test.
There was a significant difference in transcript ratio between the
liver and trachea (P¼0.0128) and between each of these and the
lung (P¼0.011) (P¼0.0047) or stomach (P¼0.0053) (P¼0.0016).
There was no significant correlation of transcript proportions with
gestational age, although only a relatively small range of
gestational ages was represented within the sample set (11–20.4
weeks).
Inter-individual differences: allelic origin of the transcripts
The a/b transcript ratio in three of the heterozygotes was
particularly imbalanced (Figure 1C, individual 2). In one of these
three cases, two tissues were available from the same individual,
and both had a very low expression of a. To interpret the source of
this asymmetry, we determined the allelic origin of the a and b
transcripts for this individual, by digesting the cDNA with AlwNI,
the enzyme used for rs4072037 genotyping in genomic DNA. The
enzyme cuts the rs4072037 A allele, which is expected to be present
in the b transcript, whereas the a transcript is expected to have the
rs4072037 G allele and would not be cut. Samples from both the
trachea and lung were tested. A ‘typical’ rs4072037 AG hetero-
zygote and an rs4072037 AA and rs4072037 GG homozygote were
used as controls. The results (Supplementary Figure 1) show that
the G allele is completely cut by the enzyme and thus does not
contribute to the b transcript in either heterozygote, and implies
AG-2
cba
Transcript positions
abc
Transcript positions
AG-1
Marker
100120 140160
c
180 200 220240 260280 300
Marker
dba
Transcript positions
GG
AG
AA
32
1
∗
Figure 1
exon 2 is shown in white. Tandem repeat domain is shown in dark grey. The positions of the single-sense primer and two antisense primers are shown with
arrows. The antisense primer downstream of the TR domain is used for amplifying the components lacking the TR domain. (B) ALF Express trace of the
RT–PCR from three individuals with different rs4072037 genotypes, using the primer in exon 1 in combination with the primer upstream of the TR domain.
The positions of the four transcripts, a, b, c and d, as well as the 100 and 300bp markers are indicated. (C) ALF Express traces from two AG heterozygous
individuals, one of whom shows very little a transcript. Samples from foetal lung; complete traces are shown in Supplementary Figure 1.
(A) Diagram of the start of MUC1 showing the positions of the PCR primers in relation to rs4072037 (asterisked). The variable extension of
MUC1 alternative splicing in human tissues
W Ng et al
980
British Journal of Cancer (2008) 99(6), 978–985
& 2008 Cancer Research UK
Genetics and Genomics

Page 4

that the G allele is less stable or poorly transcribed in the
individual with very low amounts of a transcript.
Possible genetic origin of inter-individual differences
The detection of dramatically lower amounts of a transcript in two
tissues from the same individual and the non-normal distributions
of the a/b transcript ratios suggested the possibility of a genetic
origin for some of the differences in transcript ratio. In support of
this, ratios obtained from the lung and stomach from the same
individuals showed a significant correlation (P¼0.05, data not
shown).
The possibility that the rate of transcript synthesis or transcript
stability is affected by the variable lengths of the TR domains of
MUC1 was therefore examined by testing the TR polymorphism in
the same set of foetal samples and comparing allele length ratios
with transcript ratios for the lung and stomach, the two tissues
for which the most samples were tested. Figure 3A shows an
autoradiograph of a typical Southern blot.
The haplotypes comprised of rs4072037 (G or A) and the TR
length, binned as long (L) and short (S) intronic, were inferred
using PHASE. Approximately 90% of the chromosomes have non-
recombinant haplotypes, namely, A-S (58%) or G-L (33%) with
only 5% AL and 4% GS, consistent with what was found previously
in Europeans (Fowler et al, 2003; Teixeira, 2005). Thus, one can
infer that in the majority of rs4072037 AG heterozygotes, the b
transcript encoded by the A allele carries a short TR array,
whilereas the a transcript encoded by the G allele carries a long
array. Less than 0.2% double heterozygotes (5%?4%) are
expected to have the converse arrangement.
Figure 3B shows the TR length ratios (length of the long TR
domain, typically rs4072037 G allele carrying haplotype over the
short TR domain, typically the rs4072037 A allele carrying
haplotype, see above) plotted against the a/b transcript ratios
present in the lung. There was no statistically significant
correlation for either the lung or the stomach. There was also no
significant correlation when differences in absolute length were
plotted against the transcript ratio (data not shown).
Data mining
All human exon 1 and exon 2 boundary containing MUC1
transcripts, annotated on the UCSC Browser as of June 2007, were
retrieved from the GenEMBL database. Where available, all
original literature references were examined to confirm that the
full sequence was taken from the clones reported and checked to
determine whether any composite sequences were included in the
list. For 15 of 37 annotated MUC1 sequences, literature references
were available. In 14 of the 15 referenced sequences, appropriate
sequencing appeared to have been done. In one case, the transcript
submitted was declared as a composite sequence (Ligtenberg et al,
1990).
Sequences upstream of the TR domain in exon 2 were aligned
with ClustalW. Four classes of transcripts were observed, which
were named for convenience as a, b, c and d. As most were either
short transcripts or incomplete sequences, it was not formally
possible to determine how many came from transcripts that
contain a full TR domain. The a variant is represented by
eight transcripts and the b transcripts by 26 sequences (see
Supplementary information for list), 13 of which were from HeLa
cells submitted from one laboratory (Zhang and Lu, 2003, database
submission only).
All 26 b transcripts have the rs4072037 A allele. Although five
of eight annotated a transcripts have the rs4072037 G allele, the
other three transcripts carried the A allele. All three (M32738,
AY327587 and S81781) were from cancer-derived material, but it is
noteworthy that one was from the composite sequence (Ligtenberg
et al, 1990), and one has no associated literature reference. Two c
transcripts (AF125525 and Z17325) and one d transcript (Z17325)
were also identified but the rs4072037 A/G SNP is not included
within the shorter exonic sequence of c and d so that genotype
information cannot be obtained.
Splice-prediction programs
A number of bioinformatic prediction tools (SplicePredictor:
http://deepc2.psi.iastate.edu/cgi-bin/sp.cgi, GeneSplicer: http://www.
tigr.org/tdb/GeneSplicer/gene_spl.html, Berkeley Drosophila Genome
Table 1
adult tissues and cell line samples from individuals of different genotypes for
rs4072037
Summary of splice variants a, b, c and d observed in foetal and
Genotypes AA AGGG
Splice variants present
Foetal lung
Total no.
a/d
b/c
a/b/c/d
a/trace-b
22 235
3
21
23
2a
Foetal stomach
Total no.
a/d
b/c
a/b/c/d
a/trace-b
19 185
4
19
18
1a
Foetal liver
Total no.
b/c
a/b/c/d
a/b/c
a/b/d
2
2
6
5
1
Foetal trachea
Total no.
a/d
b/c
a/b/c/d
a/b/c
371
1
3
4
3
Adult stomach
Total no.
a/d
b/c
b
a/b
a/trace-b
a/b/c/d
611 4
3
3
2
1
1a
10
Adult duodenum
Total no.
a/d
a
b
a/b/c/d
a/b/c
a/trace-b
186
3
2
1
6
2
1a
Cell lines
Total no.
a/d
b/c
a/b/c/d
342
2
3
4
aSamples that contain low amounts of transcripts not usually associated with their
genotype.
MUC1 alternative splicing in human tissues
W Ng et al
981
British Journal of Cancer (2008) 99(6), 978–985
& 2008 Cancer Research UK
Genetics and Genomics

Page 5

Project: http://www.fruitfly.org/ and NetGene2: http://www.cbs.dtu.
dk/services/NetGene2/) were also used to examine which if any of the
alternative 30splice sites was predicted by the programs. The 30splice
site for the b transcript was not predicted by any of these four
programs. SplicePredictor, however, predicted the 30splice site that is
used for the a transcript (regardless of nucleotide at rs4072037). This
is consistent with the calculated strength of the splice sites based
on the algorithm of Shapiro and Senapathy (1987), which suggested
that the strength of the 30splice site used by the a transcript is
significantly stronger than the site used for the b transcript.
The results of the analysis using the program Splice Sequences
Finder version 2.2 (http://www.umd.be/SSF), which predicts exonic
motifs, showed that three exonic splicing enhancer motifs and one
exonic splicing silencer motif overlap the rs4072037 SNP in the
300290 280 270260 250240 230220 210200190 180 170 160150
MarkerZ altZ Y alt X altY YcX Marker
Transcript positions
Figure 2
Y alt, Z, Z alt, and the 150 and 300bp markers are indicated. Samples from AA, AG and GG individuals.
Variant transcripts lacking the TR domain, detected using primers Cy5 M1ProF4 and MUC1X2R. The positions of the transcripts X, Yc, X alt,
Table 2 MUC1 ‘non-TR’ transcripts observed in the foetal sample series, subdivided according to genotype, and tissue
Genotype rs4072037 AA AGGG
Total individuals25 317
Total tissues 424810
Spliceoforms
X YcYZX alt Y alt Z altLung StomachLiver Lung StomachLiverLung Stomach
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
10 81
1
O
O
3
3
2
2
3
3
O
O
4
1
O
1
O
1
2
1
111
2
2
2
3
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
OO
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
2
1
1
1
O
O
1
3
1
O
OO
O
O
1
O
O
O
O
1
O
O
1
3
1
1
3
1
1
O
O
O
2
O
O
O
O
O
O
O
11
1
O
OO
O
O
O
O
31
O
O
O
3
1
1
1
6
1
O
3
Total2615126 1664
Presence of the ‘alt’ splice variants is correlated with the presence of the rs4072037 G, and that of X, Y and Z transcripts is correlated with the A allele.
MUC1 alternative splicing in human tissues
W Ng et al
982
British Journal of Cancer (2008) 99(6), 978–985
& 2008 Cancer Research UK
Genetics and Genomics