Schwann cells require laminin-2 throughout nerve development, because mutations in the ?2 chain in dystrophic mice interfere with
their expression and roles in development are poorly understood. Therefore, we correlated the onset of myelination in nerve and
synchronized myelinating cultures to the appearance of integrins and dystroglycan in Schwann cells. Only ?6?1 integrin is expressed
other laminin receptors, whereas coexpression of both dystroglycan and ?4 integrin is likely required for ?1-null Schwann cells to
myelinate after birth. Finally, both ?1-null and dystrophic nerves contain bundles of unsorted axons, but they are predominant in
but not laminin receptors may partially explain this. These data suggest that the action of laminin is mediated by ?1 integrins during
Schwann cells (SCs) myelinate axons in the peripheral nervous
system (PNS). SC precursors originate from neural crest at em-
bryonic day (E) 12–E13 in mouse, migrate along neurites, and
become embryonic SCs between E15 and E16 (for review, see
Jessen and Mirsky, 1999). Later, SCs segregate large axons from
axon bundles and establish a one-to-one relationship with them
(promyelinating SCs). After birth, SCs wrap axons to form mye-
lin (Webster et al., 1973), whereas non-myelin-forming SCs dif-
ferentiate after postnatal day (P) 15 (Jessen and Mirsky, 1999).
These events involve changes in cell shape and cytoskeletal orga-
nization that require adhesion to the basal lamina (BL) (Bunge,
1993) or laminin deposition (Podratz et al., 2001).
laminin-8 (?4/?1/?1) are present in the endoneurium, whereas
laminin-1 (?1/?1/?1), -9 (?4/?2/?1), and -11 (?5/?2/?1) are in
the perineurium (Sanes et al., 1990; Patton et al., 1997). Muta-
tions of the laminin ?2 chain cause congenital muscular dystro-
phy and a dysmyelinating neuropathy (Xu et al., 1994; Shorer et
consists of impaired axonal sorting, mainly in the proximal PNS
paranodal abnormalities mainly in distal nerves (Bradley et al.,
1977; Jaros and Bradley, 1979). The alterations in axonal sorting
The different timing and location of these abnormalities may
result from differential expression of laminin receptors in devel-
oping nerves. Alternatively, other laminins, or their receptors,
could differentially compensate for loss of laminin function.
In keeping with the first possibility, several laminin receptors
are present in mature SCs, mainly integrins ?6?1 and ?6?4 and
dystroglycan (DG). Integrins include ? and ? transmembrane
subunits, which form receptors for different matrix components
(for review, see Previtali et al., 2001). DG includes an ? subunit
and a trans-membrane ? subunit (Ervasti and Campbell, 1993).
Neural crest cells and SCs synthesize ?6?1 (Hsiao et al., 1991;
Bronner-Fraser et al., 1992; Einheber et al., 1993). Experiments
with blocking antibody suggest a role for ?1 in myelination
(Fernandez-Valle et al., 1994), whereas selective inactivation of
?1 in SCs impairs axonal sorting (Feltri et al., 2002). ?4 integrin
National Institutes of Health Grants NS 41319 (L.W.) and NS45630 (M.L.F.), and Amici Centro Sclerosi Multipla
(S.C.P., A.Q.). We thank C. Ferri and M. Fasolini for excellent technical assistance, Dr. G. Zanazzi for help with
5520 • TheJournalofNeuroscience,July2,2003 • 23(13):5520–5530
al., 1994; Quattrini et al., 1996), and their expression is regulated
axonally (Einheber et al., 1993; Feltri et al., 1994; Masaki et al.,
2000). ?-DG binds to laminin-2 in SC BL (Yamada et al., 1994)
and forms a complex with periaxin and dystrophic-related pro-
tein (DRP)-2 (Sherman et al., 2001). Genetic alterations of peri-
axin cause a demyelinating neuropathy (Gillespie et al., 2000;
integrin and DG in myelination has been proposed. The onset of
?6?4 and DG expression is not known.
We describe the sequential expression of laminin receptors
from embryonic nerves to the mature PNS. Precursors and im-
mature SCs expressed only ?6?1. DG expression immediately
preceded myelination, whereas ?6?4 appeared polarized after
myelination. In the absence of ?1 integrin, no compensatory
expression of ?6?4 and DG occurs prenatally, explaining the
severe prenatal defect. Dystrophic nerves, but not roots, show
upregulation of laminin-1 that may compensate for laminin-2
type of laminin and receptor mutants reflects both differences in
receptor expression and differential compensation by laminins.
Mice and genotyping
phic dy2Jmice (B6.WK-Lama2dy-2J) were from The Jackson Laboratory
have been described (Feltri et al., 1999a, 2002) and were maintained by
SCs were produced by crossing P0Cre mice with ?1 heterozygous null
mice and ?1-floxed homozygous mice as described (Graus-Porta et al.,
that were N2–N5 generations congenic for C57BL6. Mouse genotyping
was performed by Southern blot and PCR analysis of tail genomic DNA
as described previously (Kuang et al., 1998; Feltri et al., 1999a; Graus-
Porta et al., 2001). All experiments involving animals were performed
according to the Institutional Animal Care and Use Committee.
In situ hybridization
cDNAs for mouse dystroglycan, ?1, ?4, and ?6 integrins were reverse
transcribed from RNA extracted from mouse sciatic nerves as described
(Feltri et al., 1999b) using the following primers: DAG sense: 5?-GCT
CTA GAA CCC TTG AGG ACC AGG CCA C-3?; antisense: 5?-CAG
AAG CTT AAC AGT GCT TCA GAG CCA TC-3?; ?6 sense: 5?-GCT
GAA GGT GTC GTC AGT CTG AAA TC-3?; ?1 sense: 5?-GCT CTA
GCT TGA TTC CAA TGG TCC AG-3?; ?4 sense: 5?-GCT CTA GAC
into pBluescript SKII (Stratagene, La Jolla, CA), and sequenced. Gener-
ation of RNA probes and in situ hybridization was performed as de-
scribed (Previtali et al., 1999).
Antibodies and immunohistochemistry
The antibodies used are listed in Table 1. Secondary antibodies included
the following: fluorescein isothiocyanate (FITC)- or tetramethylrho-
damine isothiocyanate (TRITC)-conjugated goat anti-mouse or rat IgG
(1:50) and FITC- or TRITC-conjugated goat anti-rabbit IgG (1:100)
(Southern Biotechnology, Birmingham, AL). Peroxidase-conjugated
stain mouse tissues with mouse antibodies. Immunohistochemistry was
described in Miner et al. (1997). For immunocytochemistry, cells were
fixed 10 min in paraformaldehyde and 15 min in cold methanol. Slides
were examined with confocal (Bio-Rad MRC 1024) or fluorescence mi-
croscopy (Olympus AX and BX).
Northern blot analysis
Total RNA was extracted from sciatic nerves and analyzed by Northern
blot as described (Feltri et al., 1994), using the following cDNAs as
in situ hybridization, (2) a full-length cDNA of rat P0 (Lemke and Axel,
1985), and (3) a full-length cDNA of rat glyceraldehyde-3-phosphate
dehydrogenase (GAPDH) (Fort et al., 1985).
Previtalietal.•LamininReceptorsinPNSDevelopmentJ.Neurosci.,July2,2003 • 23(13):5520–5530 • 5521
Semiquantitative RT-PCR analysis
al., 1999b), using the following primers: laminin
?1: 5?-CACCCTGGACTTACGGCAGG-3? and
et al., 2001); GAPDH: 5?-GTATGACTCTACC-
CACGG-3? and 5?-GTTCAGCTCTGGGAT-
GAC-3?). Placentas from mouse embryos were
Western blot analysis
Sciatic nerves were dissected from 2- to
3-month-old dy2Jhomozygous or dy2Jhet-
erozygous littermates and used for Western
with the following modifications: 60 ?g of
nerve homogenates was loaded on 5% SDS-
affinity-purified rabbit anti-laminin ?1 (E3
fragment) antibodies (Durbeej et al., 1996).
Homogenates from mouse kidneys were used
as control, and equal loading of nerve homog-
enates was verified
neurofilament-M antibodies (Chemicon In-
ternational, Temecula, CA).
Preparation of purified cell cultures
Neuronal cultures. Purified dorsal root gan-
glion (DRG) neurons were dissociated from
E15.5 Sprague Dawley rats (Charles River) as
ter excision, DRG neurons were trypsinized
(0.25%; Invitrogen, San Giuliano Milanese, It-
sion (approximately three DRG neurons) was
plated as a drop onto 12 mm glass coverslips
(Greiner) coated with rat collagen (0.2 mg/ml;
Biomedical Technologies) in CB10media, con-
sisting of Eagle’s Minimal Essential Medium
(EMEM; Invitrogen) supplemented with 10%
fetal calf serum (FCS) (Biological Industries
Kibbutz), 5 mg/ml glucose (Sigma), and 50
?g/ml crude nerve growth factor (NGF) (Har-
lan or Calbiochem). To remove non-neuronal
E2F media contained EMEM supplemented with 4 mg/ml glucose, 5
?g/ml insulin (Sigma), 10 ?g/ml rat transferrin (Jackson ImmunoRe-
(Sigma), 30 nM sodium selenite (Sigma), 10 ?M 5-fluorodeoxyuridine
(Sigma), 10 ?M uridine (Sigma), and 50 ng/ml NGF.
(Feltri et al., 1992).
NGF for 1 week. To initiate myelination, cocultures were treated with
Transgenic mice and age-matched controls were killed at P28 and 6
al., 1996; Wrabetz et al., 2000).
Micrographs were digitalized using an AGFA Arcus 2 scanner, and fig-
ures were prepared using Adobe Photoshop Version 5.0.
To study laminin receptors in the SC lineage, we examined the ex-
pression of ?6, ?1, ?4 integrin subunits and DG by in situ hybrid-
E12.5. Anti-neurofilament antibodies were used to identify nerves.
Identical results were observed at E15.5 for ?6 and ?1 (Fig. 1B–
(NF) and a marker for SCs or their precursors (p75NTRreceptor)
cells (Fig. 1B–D,F–H) (and data not shown). ?4 integrin and DG
5522 • J.Neurosci.,July2,2003 • 23(13):5520–5530Previtalietal.•LamininReceptorsinPNSDevelopment
At E18.5, along with ?6 and ?1 message and protein (data not
shown), we observed the onset of ?4 integrin and DG mRNA
however, we could not yet detect ?4 and DG protein (Fig.
2C) stained for DG and blood vessels stained for ?4 (Fig. 2G).
detectable at P1 in motor but not sensory roots (Baron et al.,
1994; Forghani et al., 2001). Thus, to correlate the onset of DG
roots at P1. As expected, motor roots were positive and sensory
roots were mostly negative for MBP (Fig. 3B,D,G,I). Interest-
ingly, DG staining was also stronger in motor than sensory roots
(Fig. 3A,C,F,H). Analysis of the merged staining in the roots,
and of single fibers by cross section in the nerve, showed that
some fibers stained for both DG and MBP. The staining for DG
cross sections (Fig. 3M), indicating that DG was immediately
polarized at the ab-axonal surface of SCs. Other fibers were DG
positive, with the same ring appearance, but MBP negative (Fig.
3M, arrowhead). This indicates that DG
becomes polarized to the external SC sur-
face (facing the basal lamina), just before
the appearance of MBP. Because MBP
et al., 1987), these data suggest that DG
appears and is polarized just before wrap-
ping, in promyelinating SCs. At P5 and
P15, expression of MBP and DG progres-
sively increased in sensory roots and pe-
ripheral nerves to levels comparable with
motor roots (data not shown).
To further test the hypothesis that DG
peripheral nerves at P1 for both NF and
DG. As shown in Figure 4B, only SCs that
surrounded a single axon (arrows) ex-
pressed DG. By the same logic, we stained
mutant animals in which the absence of
either laminin ?2 or integrin ?1 causes a
subset of SCs to arrest at the stage of ax-
onal sorting. We asked whether the SCs
“frozen” at this developmental stage ex-
pressed DG. Indeed, SCs around bundles
of unsorted axons (Fig. 8E) did not show
any DG staining (Fig. 4C–E, arrowhead),
pressed DG (Fig. 4C–E). To directly visu-
alize ensheathing, DG-negative SCs, we
and p75NTRreceptor. As shown in Figure
4F–I, axon bundles are surrounded by
DG-negative, p75NTR-positive SCs (ar-
rowhead), whereas some single axon are
surrounded by a DG-positive SC (arrow),
To determine whether the levels of DG
expression were regulated during postnatal
development, we performed Northern blot
4A shows that the steady-state levels of DG mRNA increased be-
tween P10 and P15, in parallel with the increase of myelin mRNAs,
such as P0 (Fig. 4). Thus, the perinatal appearance and rise of DG
synchronized system, we stained rat SC–neuron cocultures (for
review, see Bunge, 1993) in which the onset of myelination is
triggered by the addition of ascorbic acid (Bunge, 1993). No DG
tured with DRG neurons in non-myelinating medium (Fig. 5A–
C). Only ?6 and ?1 integrins were detectable on SCs (data not
shown). Staining for DG appeared in SCs 3 d after addition of
ascorbic acid, when a minority of fibers also stained for MBP.
(Fig. 5D–F, F?–F???, arrow). As we observed in vivo, DG was
polarized even in MBP-negative fibers (F??, arrowhead). DG
staining extended longitudinally in the paranodal region (F??–
F???). The in vivo and in vitro data indicate that DG expression
immediately precedes myelination in single fibers.
Previtalietal.•LamininReceptorsinPNSDevelopment J.Neurosci.,July2,2003 • 23(13):5520–5530 • 5523
observed a faint and diffuse expression of ?4 protein in spinal
roots and peripheral nerves (Fig. 6). The diffuse staining of ?4
preceded myelination but did not correlate with its onset, be-
and motor roots (Fig. 6A,D). ?4 staining became stronger only
after MBP appeared in a single fiber and polarized outside the
compact myelin sheath, resembling its mature ab-axonal distri-
bution [Fig. 6G–I, compare left (?) with right (??) magnified
myelinating conditions expressed negligible amounts of ?4 (Fig.
5J–L). After adding myelin-promoting medium, ?4 integrin
staining was low in MBP-negative fibers but stronger and polar-
not shown), in agreement with the findings of Einheber and co-
workers (1993). Thus, these data confirm the in vivo observation
that both DG and ?4 integrin are expressed just before myelina-
tion, but ?4, in contrast to DG, is not polarized until myelin
So far we focused on pure laminin receptors, but other laminin
receptors expressed by SCs include ?1?1 integrin, a dual collag-
en–laminin receptor expressed by non-myelin-forming SCs in
mature nerves (Stewart et al., 1997), ?2?1 integrin (Hsiao et al.,
1991; Milner et al., 1997), which binds collagen, laminin, or te-
nascin depending on the cell type (Santoro, 1986; Elices and
Hemler, 1989; Languino et al., 1989), and ?7?1 integrin. We
therefore looked at the expression of ?2, ?3, and ?7 integrin
during nerve development. We found that SCs expressed very
low levels of ?2 and ?3 integrin subunits, and their expression
did not change during development (Fig. 7). ?7 integrin instead
is synthesized by SCs in mature nerves (Fig. 7I) but not in fetal
postnatal nerves (Previtali et al., 2003).
In adult ?1-null sciatic nerves, most axons are grouped in large
unsorted bundles, resembling the bundles normally found in fe-
and in roots of dystrophic mice (Bradley and Jenkison, 1973).
Interestingly, ?1-null roots are less affected than nerves (Feltri et
The differential expression of laminin-2 receptors could explain
why laminin-2 alterations produce variable effects across devel-
opment. However, diverse receptor function cannot account for
the varying topography of the phenotypes within laminin-2 and
?1 integrin mutants (roots ? nerves) and between them (roots
worse in dystrophic; nerves worse in ?1-null). To investigate this
question, we searched for compensatory expression of laminins
or their receptors in dystrophic or ?1-null roots and nerves.
?1-null nerves manifest more axonal sorting defects in nerves
than spinal roots; however, the expression of neither DG nor ?4
occurs. Not surprisingly, expression of ?2, ?3, and ?7 integrin,
which normally pair only with ?1, is similarly not upregulated
before birth in ?1-null nerves (data not shown). Thus, compen-
sation by these laminin receptors does not explain the difference
between ?1-null nerves and roots.
are indicated at the bottom of each lane, relative to the P2 value arbitrarily indicated as 1. B–E,
5524 • J.Neurosci.,July2,2003 • 23(13):5520–5530 Previtalietal.•LamininReceptorsinPNSDevelopment
After birth in ?1-null nerves, a few SCs achieve a one-to-one
relationship with axons and proceed to form myelin, albeit with
delay. The few SCs that myelinated axons were clearly ?1-
negative (Fig. 8F) (Feltri et al., 2002). To explore the expression
of DG and ?4 integrin in promyelinating versus myelinating ?1-
null Schwann cells, we first stained cross sections of ?1-null
nerves with neurofilament and then asked whether single axons
were surrounded by DG, ?4 integrin, or MBP-positive SCs. Al-
(378 fibers double stained with DG and NF out of 540 NF-
positive fibers; data not shown). Using serial sections in which
the DG-positive fibers, 30% were MBP positive and 70% were
?4 positive (Fig. 8F, 1–6), whereas MBP-negative fibers were
almost always ?4 negative (Fig. 8F, arrow). Only 1–2% of fibers
DG positive and MBP negative were faintly ?4 positive (data not
shown). These data suggest that all three receptors cooperate in
possible but delayed, and the presence of both ?6?4 and DG
correlates with myelination in ?1-null SCs.
Because ?1 integrin, in association with DG, has been proposed
to play a role in BL organization in other tissues (Henry et al.,
letion on laminins. Normally, the endo-
neurium contains laminin chains ?2, low
levels of ?4, ?1, and ?1, and the peri-
neurium contains ?1, ?4, ?5, ?1, ?2, and
?1. Laminin chains ?2, low levels of ?4,
and ?1 were present in the endoneurium
around bundles of nonsorted axons (Fig.
8H,I) (and data not shown). Instead, ?1
and ?2 laminin chains were present in the
primarily around bundles of unsorted ax-
ons (Fig. 8G) (and data not shown) where
present (Feltri et al., 2002). No laminins
sorted axons (Fig. 8G–I) (and data not
zation of normal endoneurial laminins
was detectable at this resolution, other
than the presence of perineurial laminins.
In spinal roots, laminin chains were
present similarly to controls. Laminin
chains ?2, ?4, and ?1 were detected
around SCs, whereas ?1, ?4, and ?2
chains were detected in meninges (Fig.
8J–L, compare Fig. 9A–C) (and data not
Dystrophic mice show failure of axonal
sorting that is more severe in the spinal
ference in severity could be attributable to
a differential function of laminin-2 in
roots versus nerves, e.g., via interaction
with different receptors in the two locations. To address this, we
asked whether the expression of laminin receptors was different
in roots versus nerves of normal and dystrophic animals. We
dy2Jmice (Fig. 9G–J,Q–T) (and data not shown). Although the
activation state of the receptors, particularly in dy2Jmice, cannot
be evaluated by this technique, our data do not support the hy-
pothesis that laminin has a different function in roots versus
An alternative explanation for the regional differences observed
in dystrophic mice is that another laminin compensates for the
peripheral nerves of normal and dy2Jmice.
In the spinal roots and sciatic nerves of wild-type mice, we
found expression of laminin ?2, with low levels of ?4 in the
endoneurium (Fig. 9B,C,M,N). Laminin ?1 was restricted to the
perineurium and meninges (Figs. 9A,L). In dy2Jmice, immuno-
et al., 1995). Interestingly, ?1 laminin chain was upregulated in
the endoneurium of sciatic nerves but not in roots of dy2Jmice
(Fig. 9, compare A with D, L with O). This upregulation was
Previtalietal.•LamininReceptorsinPNSDevelopmentJ.Neurosci.,July2,2003 • 23(13):5520–5530 • 5525
confirmed by semiquantitative RT-PCR
laminin chain were detectable in dy2Jho-
mozygous but not dy2Jheterozygous sci-
atic nerves. Thus, compensation by lami-
nin receptors does not explain the
difference between roots and nerves in
?1-null animals, but compensation by
laminins may well explain this difference
in dystrophic mice.
tors in SCs. We show that laminin
receptors have a hierarchy of expression,
effectors of laminin-2 at different times.
Also, we show that laminin-1 may com-
pensate for the deficiency of laminin-2 in
distal nerves but not roots of dystrophic
mice. In contrast, redundancy and com-
pensation of laminin receptors play no
operation among receptors may allow
myelination postnatally. These data are
necessary to interpret the results of gene
inactivation experiments and to produce
working hypotheses that such experi-
ments can test.
We show that ?6?1 is the major laminin receptor expressed by
expression of ?1 integrins prenatally explains why SCs are inca-
pable of sorting axons in fetal ?1-null nerves. Because this phe-
notype strongly resembles the proximal PNS of dystrophic mice,
binding of laminin-2 is likely required in early SC–axon interac-
tions. Loss-of-function experiments have not shown an obvious
role for ?1 and ?7 integrins in PNS and were not informative
because of early lethality for integrin ?2 (De Arcangelis and
Georges-Laboeusse, 2000; Previtali et al., 2003). Thus, ?6?1 in-
tegrin is likely the receptor involved in this process; however,
because many other ? partners such as ?4 and ?5 dimerize with
?1 in SCs, we cannot exclude the possibility that receptors for
inactivation of ?6 integrin in SCs will test this hypothesis.
Myelination requires cytoskeletal rearrangements in SCs as they
advance the mesaxon, eliminate cytoplasm from spirals, and
initiation of myelination. Similarly to myelin proteins, DG was
detected first in motor and then in sensory fibers (Fig. 3) (Baron
et al., 1994; Forghani et al., 2001). The polarized pattern of DG
expression, with a single axon within the DG ring, suggested that
SCs express DG at the promyelinating stage. Also, we show that
data extend previous reports on DG expression in mature SCs
et al. (2002) who reported continuous DG staining by immuno-
electron microscopy beginning in SCs in a one-to-one relation-
ship with axons. It is possible that DG is important for the onset
et al., 1999), DRP-2, and periaxin, and both periaxin mutations
neuropathy (Saito et al., 2003).
?6?4 integrin is required for the assembly of hemidesmosomes
in epithelial cells to stabilize a link between the cytoskeleton and
the BL (Nievers et al., 1999). Several authors suggested a correla-
the ab-axonal surface of SCs, parallels myelination in vivo and in
vitro, and is induced by axonal contact in development and re-
generation (Einheber et al., 1993; Feltri et al., 1994; Quattrini et
al., 1996). ?4-negative SCs from null mice form rudimental my-
elin in SC–neuron cocultures (Frei et al., 1999), however, sug-
gesting that ?6?4 is not strictly required for the onset of myeli-
it was stronger and polarized. Thus, ?6?4 may stabilize the link-
age of the BL to SCs by participating in a specialized adhesion
system similar to hemidesmosomes for epithelia. The generation
of mice null for ?4 in SCs will address this.
Expression of ?4 integrin protein in the PNS of normal P1 mice. Cryosections of motor roots (A–C), sensory roots
5526 • J.Neurosci.,July2,2003 • 23(13):5520–5530 Previtalietal.•LamininReceptorsinPNSDevelopment
Redundancy, the presence of molecules with similar function, or
compensation, the new expression of such molecules, may ex-
plain why inactivation of genes for extracellular matrix and their
receptors often produces phenotypes less severe than expected
(Hynes, 1996). We investigated redundancy and compensation
in loss-of-function of laminin-2 and one of its receptors. In the
receptor mutant, ?1-null, we previously described defects in late
fetal development. Here we show that only ?6?1 integrin was
normally present in SCs before birth, and there was no compen-
the severe defect. In contrast, we show that DG, ?6?4, and ?7?1
are coexpressed with ?6?1 at various points after a normal SC
reaches the promyelinating stage and that ?1-null SCs can my-
elinate (with delay) when they express both DG and ?6?4. Thus
DG, ?6?4, and possibly ?6?1 and ?7?1 probably cooperate in
the formation of a myelin sheath, even if their function in myeli-
nation is partially redundant. Conditional inactivation of multi-
ple receptors will be necessary to test these hypotheses.
Second, we investigated the expression of laminins and lami-
nin receptors in dystrophic mice. Interestingly, we observed ec-
topic expression of laminin chain ?1 in the endoneurium of dys-
trophic nerves but not in roots. This may explain the more severe
sorting defect seen in roots and proximal nerves of dy2Jmice
when compared with their distal nerves, because new expression
of laminin-1 may compensate for the function of laminin-2 in
axonal sorting. Our data on ?4 laminin agrees with those re-
ported on roots but differs from data reported in nerves (Patton
et al., 1997; Nakagawa et al., 2001), in that we found a similar
dystrophic mice. Possibly this difference is attributable to the dif-
ants of dystrophic mice (dy2J/dy2Jin our study vs dy/dy and dy3k/
dy3kin their studies).
naling (Colognato et al., 1999). Interac-
tion between laminin and its receptors
Yurchenco, 2000), and specific receptors,
such as DG and ?1 integrins, facilitate BL
assembly, either directly (DiPersio et al.,
1997; Henry and Campbell, 1998; Sasaki
the induction of laminin itself (Li et al.,
2002). Tsiper and Yurchenko (2002) re-
ported that DG is reorganized with lami-
nin during assembly of BL of SCs in vitro,
whereas ?1 integrin mediates the forma-
tinct from a BL and before real BL assem-
bly. Although the SCs used in their study
are removed from the physiological state
of SCs in nerves (high passage number,
ilies” of SCs that surround bundles of ax-
ons (Ziskind-Conhaim, 1988; Masaki et
al., 2002), whereas a continuous basal
lamina appears only at birth (Webster et
al., 1973). We show that only ?1 integrins
that they participate in the deposition of
the immature BL at the time of axonal
Previtalietal.•LamininReceptorsinPNSDevelopment J.Neurosci.,July2,2003 • 23(13):5520–5530 • 5527
sorting. Consistent with this, sorting is im-
null SCs that generate myelin form an ap-
parently normal BL. Therefore, ?1 is not
cruitment of ?6?4, at P1 may facilitate the
formation of the mature BL during myeli-
and ?6?4 onset coincide with the appear-
ance of a mature basal lamina, that DG is
first polarized to the outer surface of single
DG and MBP. In conclusion, we postulate
that ?1 favors the deposition of the imma-
ture BL in families of premyelinating SCs,
whereas DG organizes, and recruitment of
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