¶
* Department of Cell Biology, Department of Dermatology, and § Department of Anatomy, Faculty of Medicine, Kyoto
University, Sakyo-ku, Kyoto 606, Japan;
Laboratory of Cell Biology, KAN Research Institute Inc., Minami-Kaneda, Suita,
Osaka 564, Japan; and ¶ Department of Molecular Cell Biology, Institute of DNA Medicine, Jikei University School of Medicine,
Nishi-Shinbashi, Minato-ku, Tokyo 105, Japan
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Abstract |
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Members of the newly identified claudin gene family constitute tight junction (TJ) strands, which play a pivotal role in compartmentalization in multicellular organisms. We identified oligodendrocyte-specific protein (OSP) as claudin-11, a new claudin family member, due to its sequence similarity to claudins as well as its ability to form TJ strands in transfected fibroblasts. Claudin-11/OSP mRNA was expressed in the brain and testis. Immunofluorescence microscopy with anti-claudin-11/OSP polyclonal antibody (pAb) and anti-neurofilament mAb revealed that in the brain claudin-11/OSP-positive linear structures run in a gentle spiral around neurofilament-positive axons. At the electron microscopic level, these linear structures were identified as the so-called interlamellar strands in myelin sheaths of oligodendrocytes. In testis, well-developed TJ strands of Sertoli cells were specifically labeled with anti-claudin-11/OSP pAb both at immunofluorescence and electron microscopic levels. These findings indicated that the interlamellar strands of oligodendrocyte myelin sheaths can be regarded as a variant of TJ strands found in many other epithelial cells, and that these strands share a specific claudin species, claudin-11/OSP, with those in Sertoli cells to create and maintain the repeated compartments around axons by oligodendrocytes.
Key words: oligodendrocyte; myelin sheath; tight junction; Sertoli cell; claudin-11; oligodendrocyte-specific protein ![]() |
Introduction |
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TIGHT junctions (TJs)1 are located at the most apical
region of lateral membranes of epithelial cells, and
are thought to function as a primary barrier to the
diffusion of solutes through the paracellular pathway (for
reviews see Schneeberger and Lynch, 1992; Gumbiner, 1987
, 1993
; Anderson and van Itallie, 1995). On thin-section electron microscopy, TJ appears as a series of discrete
sites of apparent fusion, involving the outer leaflet of the
plasma membrane of adjacent cells (Farquhar and Palade,
1963
). On freeze-fracture electron microscopy, TJ appears
as a set of continuous, anastomosing intramembranous
strands or fibrils in the protoplasmic face (P-face; the outwardly facing cytoplasmic leaflet) with complementary
grooves in the extracellular face (E-face; the inwardly facing extracytoplasmic leaflet; Staehelin, 1973
, 1974
). Recent technical progress has enabled the identification of
several TJ-associated peripheral membrane proteins such
as ZO-1 (Stevenson et al., 1986
), ZO-2 (Gumbiner et al.,
1991
), ZO-3 (Balda et al., 1993
; Haskins et al., 1998
), cingulin (Citi et al., 1988
), 7H6 antigen (Zhong et al., 1993
),
and symplekin (Keon et al., 1996
), but the TJ-specific integral membrane protein, i.e., the component of TJ strands, had not been identified until recently.
Occludin, a 65-kD integral membrane protein bearing
four transmembrane domains, is the first identified component of TJ strands (Furuse et al., 1993; Ando-Akatsuka
et al., 1996
). Occludin was shown to be a component of the
TJ strand itself (Fujimoto, 1995
; Furuse et al., 1996
) and to
be directly involved in the barrier functions of TJs (McCarthy et al., 1996
; Balda et al., 1996
; Chen et al., 1997
;
Wong and Gumbiner et al., 1997). Recently, occludin gene
knockout was successfully performed, but unexpectedly
occludin-deficient epithelial cells still demonstrated a well-developed network of TJ strands, suggesting the existence
of as yet unidentified TJ-specific integral membrane proteins (Saitou et al., 1998
).
As the second and third components of TJ strands, two
22-kD integral membrane proteins each with four transmembrane domains were identified from the isolated junctional fraction of the liver (Furuse et al., 1998a). Since
these two proteins showed sequence similarity to each
other (~38% identical at the amino acid sequence level)
but not to occludin, they were designated as claudin-1 and
-2. Both proteins were targeted to and incorporated into
preexisting TJ strands when expressed in cultured epithelial cells. Furthermore, when they were introduced singly
into cultured L fibroblasts lacking TJs, they induced the
formation of a well-developed network of TJ strands between stable transfectants (Furuse et al., 1998b
). Furthermore, similarity searches in data bases identified many sequences similar to claudin-1 and -2, pointing to the existence of a new gene family, the claudin family (Morita et al.,
1999
). To date, we have identified eight members of this
family (claudin-1 to -8), which were concentrated at TJs
when introduced into cultured MDCK cells. However,
Northern blotting showed that none of these molecules
were expressed in large amounts in the central nervous system.
In the brain of vertebrates, two types of cells are known
to bear TJ or TJ-like structures; vascular endothelial cells
and oligodendrocytes. In endothelial cells in the brain, a
typical TJ strand network is well developed, which is
thought to be responsible for the blood-brain barrier (Rubin, 1991). In myelinated nerve fibers of central nervous
system, each internodal segment between two consecutive
nodes of Ranvier is composed of a cellular process of an
oligodendrocyte with its myelin lamellae. For saltatory conduction along these myelinated axons, the intercellular
spaces between axons and surrounding myelin sheaths
must be electrically isolated. In the paranodal region, numerous rows of glial-axonal (septate-like) junctions bridge
between the terminal loops of the ensheathing cell and the
underlying axonal membrane, and these junctions were
thought to be responsible for electrical sealing (Raine,
1984). Linear strands ~10 nm thick were observed between lamellae of myelin sheaths by freeze-fracture electron microscopy (Dermietzel et al., 1974, 1980; Reale et al.,
1975
; Schnapp and Mugnaini, 1978
; Tabira et al., 1978
).
These strands run parallel to the axon axis and radially
through the myelin sheath, consisting of the so-called radial component of myelin (Peters, 1961
, 1964
; Dermietzel,
1974
). Since these strands showed very similar morphological characteristics to TJ strands in epithelial and endothelial cells, the radial component was also supposed to be directly involved in isolating the extracellular compartment
within myelin sheaths (Mugnaini and Schnapp, 1974
;
Gumbiner and Louvard, 1985
). However, since any TJ-specific proteins, especially occludin or claudins, have not
yet been detected in these strands, it remains unclear whether these strands can be regarded as TJ strands not
only morphologically but also physiologically.
In this study, we analyzed the expression and subcellular
distribution of oligodendrocyte-specific protein (OSP),
partly because it shows sequence similarity to claudin-1 to
-8, and partly because it is expressed in large amounts in
the brain. The OSP cDNA was first identified as a cDNA
expressed in oligodendrocytes by subtraction cloning, but
its product has not been characterized in detail (Bronstein
et al., 1996). Here, we showed that OSP should be regarded as a member of the claudin family, and that this
molecule is a specific component of TJ strands in myelin
sheaths of oligodendrocytes, and interestingly, also in Sertoli cells of the testis.
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Materials and Methods |
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Antibodies and Cells
Rat anti-mouse occludin mAb (MOC37) was raised and characterized
as described previously (Saitou et al., 1997). Mouse anti-neurofilament 200-kD mAb and rat anti-FLAG mAb were purchased from Boehringer Mannheim Biochemicals and Eastman Kodak Co., respectively. Mouse L
cells and their transfectants were grown in DME supplemented with 10%
fetal calf serum.
cDNA Cloning and Sequencing
Kidney total RNA was isolated according the method described by Chomczynski and Sacchi (1987). Poly(A)+ was prepared from the total RNA using oligo-dT cellulose (New England Biolabs, Inc.). First strand cDNA
was prepared from this poly(A)+ RNA with SuperscriptTM II reverse transcriptase (GIBCO BRL) and used for PCR. Claudin-11/OSP cDNA was
amplified from mouse kidney first strand DNA by PCR using the previously reported sequence of mouse OSP (Bronstein et al., 1996
). The amplified cDNA was subcloned into pGEM-T Easy Vector (Promega). The
lack of sequence errors was confirmed by DNA sequence analysis using a
Dye Terminator Cycle Sequence Kit (Applied Biosystems, Inc.).
Mammalian Expression Vectors and Transfection
Mouse claudin-11/OSP was tagged with FLAG-peptide at its COOH terminus. To construct FLAG-tagged claudin-11/OSP-expression vectors,
EcoRI site was introduced at the 3'-end of claudin-11/OSP cDNA by
PCR, and amplified fragments were subcloned into pBluescript SK()-
Flag-tag. The insert was excised by SalI-XbaI digestion followed by blunting with T4-polymerase, and then introduced into pCAGGSneodelEcoRI
(Niwa et al., 1991
), which was provided by Dr. J. Miyazaki (Osaka University). Mouse L cells were used for transfection as described previously
(Furuse et al., 1998b
), and the clones stably expressing tagged protein
were screened by fluorescence microscopy with anti-FLAG mAb.
Northern Blotting
The expression of claudin-11/OSP in various mouse tissues was examined by Northern blotting using a Mouse Multiple Tissue Northern Blot (Clontech). The DNA fragment of mouse claudin-11/OSP (entire ORF) was radiolabeled with [32P]dCTP and used as a probe for Northern blotting. Hybridization was performed in ExpressHybTM Hybridization Solution (Clontech) at 68°C for 12 h. The membranes were washed with 2× SSC containing 0.1% SDS at room temperature for 30 min and then with 0.1× SSC containing 0.1% SDS at 50°C for 30 min. The membranes were exposed to imaging plates for 12 h, and the signals were visualized using a BAS2000 Bio-Imaging Analyzer (Fuji Photo Film Co. Ltd.).
Polyclonal Antibody Production
A polypeptide, CNRFYYSSGSSSPTHAKSAHV, corresponding to the COOH-terminal cytoplasmic domain of mouse claudin-11/OSP was synthesized, and coupled via cysteine to keyhole limpet hemocyanin. This conjugated peptide was used as an antigen to generate polyclonal antibodies (pAb) in rabbits. The antiserum was affinity-purified with glutathione- S-transferase (GST) fusion protein with the COOH-terminal cytoplasmic domain of claudin-11/OSP.
SDS-PAGE and Immunoblotting
Lysates of E. coli expressing GST/claudin fusion proteins were subjected
to one-dimensional SDS-PAGE (12.5%), according to the method of
Laemmli (1970), and gels were stained with Coomassie brilliant blue
R-250. For immunoblotting, proteins were electrophoretically transferred
from gels onto nitrocellulose membranes, which were then incubated with
the first antibody. Bound antibodies were detected with biotinylated second antibodies and streptavidin-conjugated alkaline phosphatase (Amersham Corp.). Nitroblue tetrazolium and bromochloroindolyl phosphate
were used as substrates for detection of alkaline phosphatase.
Immunofluorescence Microscopy
L transfectants plated on glass coverslips were fixed with 1% formaldehyde in PBS for 10 min at room temperature. Mouse brain and testis were
frozen using liquid nitrogen, and frozen sections ~10-20 µm thick were
cut on a cryostat, mounted on glass slides, air-dried, and fixed in 95% ethanol at 4°C for 30 min followed by 100% acetone at room temperature for
1 min. These samples were processed for immunofluorescence microscopy
as described previously (Furuse et al., 1998b; Morita et al., 1999
). Specimens were observed using a fluorescence microscope, Zeiss Axiophot
photomicroscope (Carl Zeiss, Inc.), or a Bio-Rad MRC 1024 confocal fluorescence microscope (Bio-Rad Laboratories) equipped with a Zeiss Axiophot photomicroscope. For each stereoscopic image (see Fig. 5), 30 optical sections (0.3-0.4-µm interval) were accumulated in the computer.
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Freeze-Fracture Electron Microscopy
For conventional freeze-fracture analysis, tissues or cultured L fibroblasts
were fixed in 2% glutaraldehyde in 0.1 M sodium cacodylate buffer (pH
7.3) for 3 h at room temperature, washed with 0.1 M sodium cacodylate
buffer three times, immersed in 30% glycerol in 0.1 M sodium cacodylate
buffer for 2 h, and then frozen in liquid nitrogen. Frozen samples were
fractured at 100°C and platinum-shadowed unidirectionally at an angle
of 45° in Balzers Freeze Etching System (BAF060; Bal-Tec). The samples
were then immersed in household bleach, and replicas floating off the
samples were washed with distilled water. Replicas were picked up on
formvar-filmed grids, and examined with a JEOL 1200EX electron microscope (JEOL) at an acceleration voltage of 100 kV.
Immunoelectron Microscopy
The immunoelectron microscopic technique for examining freeze-fracture
replicas was described in detail previously (Fujimoto, 1995; Moroi et al.,
1998
), except that samples were frozen in a high-pressure freezer (Baltec
HPM010; Bal-Tec). Immunoelectron microscopy using ultrathin cryo-sections was performed essentially according to the method developed by
Tokuyasu (Tokuyasu, 1980
; Fujimoto et al., 1992
). Samples were examined with a JEOL 1200EX electron microscope (JEOL) at an acceleration
voltage of 80 kV.
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Results |
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Characterization of OSP as a Claudin Family Member, Claudin-11
Using the previously reported nucleotide sequence of
mouse OSP (Bronstein et al., 1996), we amplified a full-length cDNA encoding mouse OSP by PCR, and confirmed that its open reading frame encoded a protein of
207 amino acids with a calculated molecular mass of 22.1 kD.
OSP showed rather weak sequence similarity to claudins: it was almost equidistantly related to previously identified
members of the claudin family (claudin-1 to -8; ~30%
identity at the amino acid sequence level to each member).
As shown in Fig. 1, comparison between OSP and claudin-1
revealed that identical amino acids were almost evenly distributed throughout these molecules.
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Next, we introduced cDNA encoding OSP with a FLAG-
sequence at its COOH terminus into cultured L fibroblasts
which lacked TJs or the expression of claudins (Furuse et
al., 1998b). Immunofluorescence microscopy of the stable
transfectants with anti-FLAG mAb showed that expressed
FLAG-OSP was concentrated at cell-cell borders as planes
or on thin cellular protrusions (Fig. 2, a-d). This mAb
gave no signal from parent L fibroblasts. Then, these stable L transfectants expressing FLAG-OSP were fixed with
glutaraldehyde and examined by conventional freeze-fracture electron microscopy (Fig. 2 e). In these cells, TJ
strand/groove-like structures were frequently observed to
be arranged in a parallel manner, whereas in parent L cells
these structures were not detected. These strands were associated with the P-face, and were mostly discontinuous with intervening spaces of various widths (Fig. 2 e, inset).
On the E-face, complementary continuous grooves were
identified, containing scattered particles (Fig. 2 e, inset).
The OSP-induced strands did not bifurcate frequently and
showed a tendency to run parallel to each other.
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These characteristics of OSP, i.e., sequence similarity to claudins and ability to induce TJ strand/groove-like structures in L fibroblasts, led us to regard OSP as a member of the claudin family, and we tentatively designated it as claudin-11 after consulting the human gene nomenclature committee (http://www.gene.ucl.ac.uk/nomenclature/). (In the updated human gene database, at least 15 members of the claudin family were found, all of which were already assigned to claudin-1 to -15.)
Expression and Distribution of Claudin-11/OSP in Brain
We next examined the expression of claudin-11/OSP in various tissues by Northern blotting. As shown in Fig. 3 A, claudin-11/OSP mRNA was detected as a 2.3-kb band in large amounts in the brain and testis and in only a trace amount in the kidney, suggesting that this type of claudin is involved in the TJ formation specifically in the brain and testis. Then, to examine the subcellular distribution of claudin-11/OSP, we generated polyclonal antibodies (pAbs) in rabbits using a synthesized peptide corresponding to COOH-terminal 20 amino acids of claudin-11/ OSP as an antigen. By immunoblotting, one affinity-purified pAb (pAb CL11-2) specifically recognized the GST fusion protein with COOH-terminal cytoplasmic domain of claudin-11/OSP, but not that of claudin-1 to -8, which were produced in E. coli (Fig. 3 B). Using this pAb, we first examined the subcellular distribution of claudin-11/OSP in the brain. When frozen sections of mouse brain were immunofluorescently stained with anti-claudin-11/OSP pAb, a large number of intensely stained linear structures were seen scattered in random directions in the cortex (Fig. 4 a). In deeper regions, these linear structures were occasionally arranged in a parallel manner to form thick bundles (Fig. 4 b). In the brain, TJs are known to be developed in vascular endothelial cells. Since these TJs were stained positively with anti-occludin antibody, we then stained frozen sections of brain doubly with anti-claudin-11/OSP pAb and anti-occludin mAb. However, as shown in Fig. 4, c and d, the claudin-11-positive linear structures did not overlap with occludin-positive endothelial TJs.
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Then, frozen sections of the brain cortex were doubly stained with anti-claudin-11/OSP pAb and anti-neurofilament mAb, examined by confocal microscopy, and stereoscopic images were generated by computer (Fig. 5). At higher magnification, each claudin-11/OSP-positive linear structure was seen to run in a gentle spiral around a neurofilament-positive axon. These images suggested that these claudin-11/OSP signals were derived from myelin sheaths surrounding individual axons.
As reported previously (Dermietzel et al., 1974, 1980;
Reale et al., 1975; Schnapp and Mugnaini, 1978
; Tabira et al.,
1978
), conventional freeze-fracture electron microscopy of
glutaraldehyde-fixed mouse brain revealed that so-called
interlamellar strands of oligodendrocytes were arranged in
a gentle spiral around axons (Fig. 6 a). Similarly to TJ
strands in L transfectants expressing claudin-11/OSP (see Fig. 2), these interlamellar strands were associated with
the P-face, and were mostly discontinuous with intervening spaces of various widths (Fig. 6 a, inset). When freeze-fracture replicas from unfixed brains or optic nerves were
immunolabeled with anti-claudin-11/OSP pAb, these interlamellar strands were specifically labeled (Fig. 6, b and
c). Furthermore, as shown in Fig. 7, when ultrathin cryo-sections of the brain were incubated with the same pAb,
transverse sections of myelin sheaths were labeled radially, which may correspond to the so-called radial component of myelin (Peters, 1961
, 1964
; Dermietzel, 1974
).
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Distribution of Claudin-11/OSP in Testis
Finally, frozen sections of mouse testis were doubly stained with anti-claudin-11/OSP pAb and anti-occludin mAb. As shown in Fig. 8, a and b, both claudin-11/OSP and occludin were concentrated and precisely colocalized in a linear fashion at the most basal region of lateral membranes of adjacent Sertoli cells where TJs were reported to be well developed. Endothelial cells of microvessels were occludin-positive, but claudin-11/OSP-negative (Fig. 8, a and b). Immunofreeze-fracture electron microscopy revealed that claudin-11/OSP was exclusively localized on well-developed TJ strands of Sertoli cells (Fig. 8 c).
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Discussion |
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Interlamellar strands (radial components) of myelin sheaths
are of great interest in terms of the physiological functions of oligodendrocytes (see Schnapp and Mugnaini, 1978).
Although their appearance on freeze-fracture images is
similar to those of epithelial and/or endothelial TJs, TJ-specific proteins, especially occludin, have not been shown
to be localized at these interlamellar strands. On the other
hand, we recently identified novel gene family members,
claudin-1 to -8, which are major constituents of TJ strands,
and found that single or several claudins are copolymerized to form TJ strands in various tissues (Furuse et al.,
1998a
,b; Morita et al., 1999
). However, Northern blotting
revealed that they were not expressed in large amounts in
the brain as compared with non-neuronal tissues (Furuse
et al., 1998a
; Morita et al., 1999
). In this study, we found
that OSP (oligodendrocyte-specific protein) shows a
sequence similarity to claudins, although the degree of
identity was at most ~30% (see Fig. 1). OSP was first identified as a protein specifically expressing in oligodendrocytes, but it has not been characterized in detail (Bronstein et al., 1996
). We have demonstrated that OSP has the
ability to form TJ strand-like structures in L fibroblasts,
and that it is exclusively localized at interlamellar strands.
Based on these observations, we concluded that interlamellar strands can be regarded as a variant of TJ strands
composed of a new claudin, claudin-11/OSP.
As previously reported, when claudin-1 or -2 was singly
expressed in L fibroblasts, TJ strands were induced, and
through their ramification a huge network of strands was
formed (Furuse et al., 1998b). In contrast, the claudin-11/
OSP-induced strands scarcely branched in L fibroblasts,
and showed a tendency to run parallel to each other. Interestingly, interlamellar strands (and also TJ strands in Sertoli cells [Gilula et al., 1976
]) run parallel without branching (see Figs. 6 and 8), while typical TJ strands in epithelial
cells frequently ramify to form networks (Staehelin, 1973
,
1974
). These findings favored the notion that claudin-11/ OSP is a major constituent of interlamellar strands (and
also TJ strands in Sertoli cells) and that the frequency of
ramification of strands depends on the intrinsic nature of
each claudin species.
It is intriguing that TJ strands in oligodendrocytes (interlamellar strands) share a specific claudin species, claudin-11/OSP, with those in Sertoli cells. In the testis, well-developed TJ strands in Sertoli cells (so-called Sertoli
junctions) closely protect spermatogenic cells from the external environment, which is known as the blood-testis
barrier (Dym and Fawcett, 1970; Russell and Peterson,
1985
). Similarly to the brain, Northern blotting analysis indicated that the testis does not express claudin-1 to -8 in
large amounts (Furuse et al., 1998a
; Morita et al., 1999
). Therefore, it is likely that in the testis claudin-11/OSP is a major component of TJ strands, which function as a tight
barrier, and that in the brain interlamellar strands of oligodendrocytes also function as a barrier to closely isolate the
extracellular compartment within myelin sheaths. In the
central nervous system, neurons are also closely protected
from the external environment, but this blood-brain barrier is known to be established by TJ strands in vascular
endothelial cells in vertebrates (Rubin, 1991
). However, in
invertebrates such as insects, TJs of the perineurial sheath
in the central nervous system (Lane et al., 1994
) and/or pleated septate junctions (possible invertebrate equivalent
of TJs) of glia cells were reported to be directly involved in
the blood-nerve barrier (Lane et al., 1977
; Juang and Carlson, 1992
; Baumgartner et al., 1996
). It is still premature to
discuss this issue further, but it would be interesting to examine the phylogenetical relationship between claudin-11/
OSP and the other claudins in future studies.
Sertoli junctions were initially called "the junctional
specializations of Sertoli cells" (Flickinger and Fawcett,
1967), and thought to be different from typical TJs in other
epithelial cells (Gilula et al., 1976
). These Sertoli junctions
were characterized by (a) discrete bundles of filaments
running parallel to the junction membranes, (b) cisternae
of the endoplasmic reticulum located deeper to the layer
of filaments, and (c) the parallelly arranged strands that
did not anastomose extensively. However, recent findings on the localization of ZO-1 (Byers et al., 1991
; Balda and
Anderson, 1993
), symplekin (Keon et al., 1996
), and occludin (Moroi et al., 1998
) in Sertoli junctions indicated that
this specialization is a variant of TJs found in many other
epithelia. This study, i.e., the occurrence of claudin-11/
OSP in Sertoli junctions, conclusively supported this notion.
Another issue that we should discuss here is the sequence differences in the cytoplasmic tail between claudin-11/OSP and the other claudins. All of claudin-1 to -8 end in -Y-V at their COOH termini (Furuse et al., 1998a;
Morita et al., 1999
), whereas only claudin-11/OSP ends in
-H-V. In this sense, claudin-11/OSP is rather distantly related to the other claudins. The COOH-terminal -E-S/T-D-V motif in the Shaker K+ channel (-ETDV)/NMDA R2
subunit (-ESDV) and -E-Y-Y-V motif in neurexins were
shown to be responsible for their binding to PDZ domains
of Dlg/PSD-95 family proteins and LIN-2/CASK, respectively (Kim et al., 1995
; Komau et al., 1995
; Hata et al.,
1996
; Niethammer et al., 1996
). Considering that three
PDZ-containing MAGUK family proteins, ZO-1, ZO-2,
and ZO-3, are exclusively concentrated at the cytoplasmic
surface of TJ strands in epithelial and endothelial cells
(Stevenson et al., 1986
; Gumbiner et al., 1991
; Balda et al.,
1993
; Itoh et al., 1993
; Willott et al., 1993
; Jesaitis and Goodenough, 1994
; Haskins et al., 1998
), it is expected
that the COOH-terminal -Y-V in claudin-1 to -8 binds to
some of the PDZ domains of the MAGUK family proteins
to recruit them to TJ strands. So far, occludin has been regarded as a membrane binding partner for ZO-1 and ZO-2
(Furuse et al., 1994
; Itoh et al., 1999
), but it was shown that
even in occludin-deficient TJ strands ZO-1 (and also ZO-2;
unpublished data) was still recruited (Saitou et al., 1998
).
These findings are consistent with the above expectation, and led to the further speculation that the COOH-terminal -H-V of claudin-11/OSP shows distinct affinity to ZO-1,
ZO-2, and/or ZO-3 from the other claudins. Actually, ZO-1
and ZO-2 were not concentrated at the interlamellar
strands of oligodendrocytes (data not shown; see Saitou et al.,
1997
).
In this study, we found that although the amino acid sequence of claudin-11/OSP is fairly diversified from the eight previously identified claudins, it has the ability to induce TJ strands in L fibroblasts and constitutes the interlamellar strands in oligodendrocytes as well as TJ strands of Sertoli cells in the testis. Molecular manipulation of claudin-11/OSP including targeted gene disruption will more directly unravel not only the physiological functions of this unique claudin family member in the brain and testis, but also the etiologies of some myelin-related as well as spermatogenesis-related disorders.
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Footnotes |
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Address correspondence to Shoichiro Tsukita, Department of Cell Biology, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan. Tel.: 81 75 753 4372. Fax: 81 75 753 4660. E-mail: htsukita{at}mfour.med.kyoto-u.ac.jp
Received for publication 15 January 1999 and in revised form 16 March 1999.
The first two authors contributed equally to this work.
We thank all the members of our laboratory (Department of Cell Biology, Faculty of Medicine, Kyoto University) for helpful discussions. Our thanks are also due to Ms. K. Furuse for her excellent technical assistance.
This study was supported in part by a Grant-in-Aid for Cancer Research and a Grant-in-Aid for Scientific Research (A) from the Ministry of Education, Science and Culture of Japan to Sh. Tsukita.
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Abbreviations used in this paper |
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E-face, extracellular face; GST, glutathione-S-transferase; OSP, oligodendrocyte-specific protein; P-face, protoplasmic face; pAb, polyclonal antibody; TJ, tight junction.
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References |
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---|
1. |
Anderson, J.M., and
C.M. Van Itallie.
1995.
Tight junctions and the molecular
basis for regulation of paracellular permeability.
Am. J. Physiol.
269:
G467-G475
|
2. | Ando-Akatsuka, Y., M. Saitou, T. Hirase, M. Kishi, A. Sakakibara, M. Itoh, S. Yonemura, M. Furuse, and Sh. Tsukita. 1996. Interspecies diversity of the occludin sequence: cDNA cloning of human, mouse, dog, and rat-kangaroo homologues. J. Cell Biol. 133: 43-47 [Abstract]. |
3. |
Balda, M.S., and
J.M. Anderson.
1993.
Two classes of tight junctions are revealed by ZO-1 isoforms.
Am. J. Physiol.
264:
C918-C924
|
4. | Balda, M.S., L. González-Mariscal, K. Matter, M. Cereijido, and J.M. Anderson. 1993. Assembly of the tight junction: the role of diacylglycerol. J. Cell Biol. 123: 293-302 [Abstract]. |
5. | Balda, M.S., J.A. Whitney, C. Flores, S. González, M. Cereijido, and K. Matter. 1996. Functional dissociation of paracellular permeability and transepithelial electrical resistance and disruption of the apical-basolateral intramembrane diffusion barrier by expression of a mutant tight junction membrane protein. J. Cell Biol. 134: 1031-1049 [Abstract]. |
6. | Baumgartner, S., J.T. Littleton, K. Broadie, M.A. Bhat, R. Harbecke, J.A. Lengyel, R. Chiquet-Ehrismann, A. Prokop, and H.J. Bellen. 1996. A Drosophila neurexin is required for septate junction and blood-nerve barrier formation and function. Cell. 87: 1059-1068 |
7. | Bronstein, J.M., P. Popper, P.E. Micevych, and D.B. Farber. 1996. Isolation and characterization of a novel oligodendrocyte-specific protein. Neurology. 47: 772-778 [Abstract]. |
8. | Byers, S., R. Graham, H.N. Dai, and B. Hoxter. 1991. Development of Sertoli cell junctional specializations and the distribution of the tight-junction-associated protein ZO-1 in the mouse testis. Am. J. Anat. 191: 35-47 |
9. | Chomczynski, P., and N. Sacchi. 1987. Single-step method of RNA isolation by acid guanidinium thiocyanate-phenol-chloroform extraction. Anal. Biochem. 162: 156-159 |
10. |
Chen, Y.-H.,
C. Merzdorf,
D.L. Paul, and
D.A. Goodenough.
1997.
COOH terminus of occludin is required for tight junction barrier function in early Xenopus embryos.
J. Cell Biol.
138:
891-899
|
11. | Citi, S., H. Sabanay, R. Jakes, B. Geiger, and J. Kendrick-Jones. 1988. Cingulin, a new peripheral component of tight junctions. Nature. 333: 272-276 |
12. | Dermietzel, R.. 1974. Junctions in the central nervous system of the cat. I. Membrane fusion in central myelin. Cell Tissue Res. 148: 565-576 |
13. | Dermietzel, R., A.G. Leibstein, and D. Schunke. 1980. Interlamellar tight junctions of central myelin: II. A freeze-fracture and cytochemical study on their arrangement and composition. Cell Tissue Res. 213: 95-108 |
14. | Dym, M., and D.W. Fawcett. 1970. The blood-testis barrier in the rat and the physiological compartmentation of the seminiferous epithelium. Biol. Reprod. 3: 308-326 |
15. |
Farquhar, M.G., and
G.E. Palade.
1963.
Junctional complexes in various epithelia.
J. Cell Biol.
17:
375-412
|
16. | Flickinger, C., and D.W. Fawcett. 1967. The junctional specializations of Sertoli cells in the seminiferous epithelium. Anat. Rec. 158: 207-222 |
17. |
Fujimoto, K..
1995.
Freeze-fracture replica electron microscopy combined with
SDS digestion for cytochemical labeling of integral membrane proteins. Application to the immunogold labeling of intercellular junctional complexes.
J. Cell Sci.
108:
3443-3449
|
18. | Fujimoto, T., S. Nakade, A. Miyawaki, K. Mikoshiba, and K. Ogawa. 1992. Localization of inositol 1,4,5-trisphosphate receptor-like protein in plasmalemmal caveolae. J. Cell Biol. 119: 1507-1513 [Abstract]. |
19. |
Furuse, M.,
K. Fujimoto,
N. Sato,
T. Hirase,
Sa. Tsukita, and
Sh. Tsukita.
1996.
Overexpression of occludin, a tight junction-associated integral membrane
protein, induces the formation of intracellular multilamellar bodies bearing
tight junction-like structures.
J. Cell Sci.
109:
429-435
|
20. | Furuse, M., T. Hirase, M. Itoh, A. Nagafuchi, S. Yonemura, Sa. Tsukita, and Sh. Tsukita. 1993. Occludin: a novel integral membrane protein localizing at tight junctions. J. Cell Biol. 123: 1777-1788 [Abstract]. |
21. | Furuse, M., M. Itoh, T. Hirase, A. Nagafuchi, S. Yonemura, Sa. Tsukita, and Sh. Tsukita. 1994. Direct association of occludin with ZO-1 and its possible involvement in the localization of occludin at tight junctions. J. Cell Biol. 127: 1617-1626 [Abstract]. |
22. |
Furuse, M.,
K. Fujita,
T. Hiiragi,
K. Fujimoto, and
Sh. Tsukita.
1998a.
Claudin-1
and -2: novel integral membrane proteins localizing at tight junctions with
no sequence similarity to occludin.
J. Cell Biol.
141:
1539-1550
|
23. |
Furuse, M.,
H. Sasaki,
K. Fujimoto, and
Sh. Tsukita.
1998b.
A single gene product, claudin-1 or -2, reconstitutes tight junction strands and recruits occludin
in fibroblasts.
J. Cell Biol.
143:
391-401
|
24. | Gilula, N.B., D.W. Fawcett, and A. Aoki. 1976. The Sertoli cell occluding junctions and gap junctions in mature and developing mammalian testis. Dev. Biol. 50: 142-168 |
25. |
Gumbiner, B..
1987.
Structure, biochemistry, and assembly of epithelial tight
junctions.
Am. J. Physiol.
253:
C749-C758
|
26. | Gumbiner, B.. 1993. Breaking through the tight junction barrier. J. Cell Biol. 123: 1631-1633 |
27. | Gumbiner, B., and D. Louvard. 1985. Localized barriers in the plasma membrane: a common way to form domains. Trends Biochem. Sci. 10: 435-438 . |
28. | Gumbiner, B., T. Lowenkopf, and D. Apatira. 1991. Identification of a 160 kDa polypeptide that binds to the tight junction protein ZO-1. Proc. Natl. Acad. Sci. USA. 88: 3460-3464 [Abstract]. |
29. |
Haskins, J.,
L. Gu,
E.S. Wittchen,
J. Hibbard, and
B.R. Stevenson.
1998.
ZO-3,
a novel member of the MAGUK protein family found at the tight junction,
interacts with ZO-1 and occludin.
J. Cell Biol.
141:
199-208
|
30. | Hata, Y., S. Butz, and T.C. Sudhof. 1996. CASK: a novel dlg/PSD95 homolog with an N-terminal calmodulin-dependent protein kinase domain identified by interaction with neurexins. J. Neurosci. 16: 2488-2494 [Abstract]. |
31. | Itoh, M., A. Nagafuchi, S. Yonemura, T. Kitani-Yasuda, Sa. Tsukita, and Sh. Tsukita. 1993. The 220-kD protein colocalizing with cadherins in non-epithelial cells is identical to ZO-1, a tight junction-associated protein in epithelial cells: cDNA cloning and immunoelectron microscopy. J. Cell Biol. 121: 491-502 [Abstract]. |
32. |
Itoh, M.,
K. Morita, and
Sh. Tsukita.
1999.
Characterization of ZO-2 as a
MAGUK family member associated with tight and adherens junctions with
a binding affinity to occludin and ![]() |
33. | Jesaitis, L.A., and D.A. Goodenough. 1994. Molecular characterization and tissue distribution of ZO-2, a tight junction protein homologous to ZO-1 and the Drosophila discs-large tumor suppresser protein. J. Cell Biol. 124: 949-961 [Abstract]. |
34. | Juang, J.-L., and S.D. Carlson. 1992. A blood-brain barrier without tight junctions in the fly central nervous system in the early postembryonic stage. Cell Tissue Res. 270: 95-103 . |
35. | Keon, B.H., S. Schäfer, C. Kuhn, C. Grund, and W.W. Franke. 1996. Symplekin, a novel type of tight junction plaque protein. J. Cell Biol 134: 1003-1018 [Abstract]. |
36. | Kim, E., M. Niethammer, A. Rothschild, Y.N. Jan, and M. Sheng. 1995. Clustering of Shaker-type K+ channels by interaction with a family of membrane-associated guanylate kinases. Nature. 378: 85-88 |
37. | Komau, H.-C., L.T. Schenker, M.B. Kennedy, and P.H. Seeburg. 1995. Domain interaction between NMDA receptor subunits and the postsynaptic density protein PSD-95. Science. 269: 1737-1740 |
38. | Laemmli, U.K.. 1970. Cleavage of structural proteins during the assembly of the head of bacteriophage T4. Nature. 227: 680-685 |
39. | Lane, N.J., H.I. Skaer, and L.S. Swales. 1977. Intercellular junctions in the central nervous system of insects. J. Cell Sci. 26: 175-199 [Abstract]. |
40. | Lane, N.J., R. Dallai, G. Martinucci, and P. Burigbel. 1994. Electron microscopic structure and evolution of epithelial junctions. In Molecular Mechanisms of Epithelial Cell Junctions: From Development to Disease. S. Citi, editor. R.G. Landes, Austin, TX. 23-44. |
41. |
McCarthy, K.M.,
I.B. Skare,
M.C. Stankewich,
M. Furuse,
Sh. Tsukita,
R.A. Rogers,
R.D. Lynch, and
E.E. Schneeberger.
1996.
Occludin is a functional
component of the tight junction.
J. Cell Sci.
109:
2287-2298
|
42. |
Morita, K.,
M. Furuse,
K. Fujimoto, and
Sh. Tsukita.
1999.
Claudin multigene
family encoding four-transmembrane domain protein components of tight
junction strands.
Proc. Natl. Acad. Sci. USA.
96:
511-516
|
43. |
Moroi, S.,
M. Saitou,
K. Fujimoto,
A. Sakakibara,
M. Furuse,
O. Yoshida, and
Sh. Tsukita.
1998.
Occludin is concentrated at tight junctions of mouse/rat
but not human/guinea pig Sertoli cells in testes.
Am. J. Physiol.
274:
C1708-C1717
|
44. | Mugnaini, E., and B. Schnapp. 1974. Possible role of zonula occludens of the myelin sheath in demyelination condition. Nature. 251: 725-727 |
45. | Niethammer, M., E. Kim, and M. Sheng. 1996. Interaction between the C terminus of NMDA receptor subunits and multiple members of the PSD-95 family of membrane-associated guanylate kinases. J. Neurosci. 16: 2157-2163 [Abstract]. |
46. | Niwa, H., K. Yamamura, and J. Miyazaki. 1991. Efficient selection for high-expression transfectants with a novel eukaryotic vector. Gene. 108: 193-200 |
47. |
Peters, A..
1961.
A radial component of central myelin sheaths.
J. Biophys. Biochem. Cytol.
11:
733-735
.
|
48. |
Peters, A..
1964.
Further observations on the structure of myelin sheaths in the
central nervous system.
J. Cell Biol.
20:
281-296
|
49. | Rane, C.S. 1984. Morphology of myelin and myelination. In Myelin. P. Morell, editor. 2nd edition. Plenum Press, New York. 1-50. |
50. | Reale, E., L. Luciano, and M. Spitznas. 1975. Zonulae occludentes of the myelin lamellae in the nerve fibre layer of the retina and in the optic nerve of the rabbit: a demonstration by the freeze-fracture method. J. Neurocytol. 4: 131-140 |
51. | Rubin, L.L.. 1991. The blood-brain barrier in and out of cell culture. Curr. Opin. Neurobiol. 1: 360-363 |
52. | Russell, L.D., and R.N. Peterson. 1985. Sertoli cell junctions: morphological and functional correlates. Int. Rev. Cytol 94: 177-211 |
53. | Saitou, M., Y. Ando-Akatsuka, M. Itoh, M. Furuse, J. Inazawa, K. Fujimoto, and Sh. Tsukita. 1997. Mammalian occludin in epithelial cells: its expression and subcellular distribution. Eur. J. Cell Biol. 73: 222-231 |
54. |
Saitou, M.,
K. Fujimoto,
Y. Doi,
M. Itoh,
T. Fujimoto,
M. Furuse,
H. Takano,
T. Noda, and
Sh. Tsukita.
1998.
Occludin-deficient embryonic stem cells can
differentiate into polarized epithelial cells bearing tight junctions.
J. Cell
Biol.
141:
397-408
|
55. | Schnapp, B., and E. Mugnaini. 1978. Membrane architecture of myelinated fibers as seen by freeze-fracture. In Physiology and Pathology of Axons. S.G. Waxman, editor. Raven Press, New York. 83-123. |
56. |
Schneeberger, E.E., and
R.D. Lynch.
1992.
Structure, function, and regulation
of cellular tight junctions.
Am. J. Physiol.
262:
L647-L661
|
57. | Staehelin, L.A.. 1973. Further observations on the fine structure of freeze-cleaved tight junctions. J. Cell Sci. 13: 763-786 |
58. | Staehelin, L.A.. 1974. Structure and function of intercellular junctions. Int. Rev. Cytol. 39: 191-283 |
59. | Stevenson, B.R., J.D. Siliciano, M.S. Mooseker, and D.A. Goodenough. 1986. Identification of ZO-1: a high molecular mass polypeptide associated with the tight junction (zonula occludens) in a variety of epithelia. J. Cell Biol. 103: 755-766 [Abstract]. |
60. | Tabira, T., M.J. Cullen, P.J. Reier, and H.F. de Webster. 1978. An experimental analysis of interlamellar tight junctions in amphibian and mammalian C.N.S. myelin. J. Neurocytol. 7: 489-503 |
61. | Tokuyasu, K.T.. 1980. Immunochemistry on ultrathin frozen sections. Histochem. J. 12: 381-403 |
62. |
Willott, E.,
M.S. Balda,
A.S. Fanning,
B. Jameson,
C. Van Itallie, and
J.M. Anderson.
1993.
The tight junction protein ZO-1 is homologous to the
Drosophila discs-large tumor suppresser protein of septate junctions.
Proc.
Natl. Acad. Sci. USA.
90:
7834-7838
|
63. |
Wong, V., and
B.M. Gumbiner.
1997.
A synthetic peptide corresponding to the
extracellular domain of occludin perturbs the tight junction permeability
barrier.
J. Cell Biol.
136:
399-409
|
64. | Zhong, Y., T. Saitoh, T. Minase, N. Sawada, K. Enomoto, and M. Mori. 1993. Monoclonal antibody 7H6 reacts with a novel tight junction-associated protein distinct from ZO-1, cingulin, and ZO-2. J. Cell Biol. 120: 477-483 [Abstract]. |