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Molecular, Cellular and Developmental Biology Program (J.T.F., M.N.-H.) and the Departments of Zoology and Genetics (J.T.F.) and Biochemistry, Biophysics, and Molecular Biology (M.N.-H.), Iowa State University, Ames, Iowa 50011
Address all correspondence and requests for reprints to: Dr. Marit Nilsen-Hamilton, Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, 3206 Molecular Biology Building, Ames, Iowa 50011-3260. E-mail: marit{at}iastate.edu
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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. Transgenic mice, expressing
lacZ under the combined control of the cytomegalovirus
immediate early enhancer and the Mrp3 flanking
sequences, demonstrate wound- and hair cycle-induced transgene
expression. These results show that elements within the flanking
regulatory sequences of the Mrp3 gene are involved in
the activation of Mrp3 in response to these events. The
results reported here suggest that MRP3 may participate in wound
healing and hair follicle cycle as a growth factor and/or angiogenesis
factor. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Growth factors, including FGF5, FGF7, epidermal growth factor (EGF),
and transforming growth factor- (TGF) are also involved in hair
follicle morphogenesis, as evidenced by the hair-associated
abnormalities linked to mutations or introduced knockouts of these
genes or their receptors (7, 8). The hair follicle
contains stem cells that probably contribute to cutaneous wound healing
by providing a source of the keratinocytes that migrate and proliferate
to repair the wound (9).
The mitogen-regulated protein/proliferins (MRP/PLFs) are a group of highly homologous, well characterized, growth factor-inducible secondary response genes and members of the PRL/GH family. In immortalized mesenchymal cells derived from mouse embryos (3T3 cells), Mrp/Plf expression is increased in response to bFGF and other growth factors (10). Expression of Mrp/Plf is greater in growing than in quiescent cells (11). This may be explained in part by the fact that TGFß inhibits Mrp/Plf expression in quiescent, but not in growing, cells (12).
There are between four and six Mrp/Plf genes (13), and the four cloned complementary DNAs (cDNAs; Plf1, Plf2, Mrp3, and Mrp4) are highly identical to one another (14, 15). Although some nonplacental cell lines express Mrp/Plfs in vitro, the only tissue identified in the mouse in which Mrp/Plf expression was identified until recently is the placenta (16). Mrp/Plf expression is localized to the trophoblastic giant cells, which secrete high levels of MRP/PLFs during midgestation (17, 18). Placental MRP/PLFs are believed to be angiogenesis factors in the fetal placenta. PLF1 stimulates angiogenesis by interacting with the mannose 6-phosphate receptor (19). It is also a growth factor for uterine cells acting through a separate receptor in the uterus that does not recognize mannose-6-phosphate (20, 21). Thus, the MRP/PLFs are believed to coordinate aspects of fetal and maternal development during pregnancy through their ability to regulate cell proliferation and angiogenesis.
Because growth factors are expressed at high levels during wound healing, and the Mrp/Plfs are highly up-regulated by growth factors in 3T3 cells, we investigated the possibility that Mrp/Plf expression might also be increased during wound repair. Here we demonstrate that Mrp3 is expressed specifically in suprabasal keratinocytes at the wound site, and its expression is regulated temporally during cutaneous wound healing. MRP/PLF protein and RNA expression are also regulated during the hair follicle cycle, during which immunohistochemistry reveals the protein predominantly in the outer root sheath. The same distribution and regulation of expression were found in transgenic mice expressing a lacZ transgene under combined control of the cytomegalovirus immediate early (CMV-IE) enhancer and the Mrp3 flanking sequences. We also show that Mrp3 expression is induced by keratinocyte growth factor (KGF; FGF 7) in primary cultures of keratinocytes. These data suggest that MRP3 plays a role during cutaneous wound repair and in the hair follicle cycle. A likely regulator of Mrp3 gene expression in the skin is KGF.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Polyclonal anti-MRP/PLF rabbit serum and preimmune serum were prepared as described previously (22). Plasmid vector pckt17–2, a modified pSP73 (Promega Corp., Madison, WI), was a gift from Christopher Tuggle (Iowa State University). KGF was purchased from R & D Systems, Inc. (Minneapolis, MN).
Wound healing experiments
FVB mice (Charles River Laboratories, Inc.) were
used for most wound healing experiments, except for experiments
performed on transgenic animals, which were either FVB or FVB/CF-1
crosses. To produce wounds, adult mice were anesthetized using
Avertin, prepared as previously described (23), and
scissors were used to make 0.5- to 1-cm full thickness skin wounds
laterally along the back. Two equally spaced nylon sutures (5–0
ethilon, Ethicon, Somerville, NJ) were used to close each 1-cm wound in
the back. In some cases the tip of the tail was cut off to produce a
wound and for use in identifying transgenic offspring. At various times
after wounding, the wound tissue was removed and either fixed for
immunohistochemistry or frozen in liquid nitrogen and stored at -70 C
until used for RNA isolation.
Depilation experiments
For depilation experiments, adult mice C57/BL6xCF-1 (6–8
weeks) were anesthetized with Avertin, and the hair was removed using a
mixture of bees wax and rosin (ZIP, Lee Pharmaceuticals, South El
Monte, CA). The day of depilation was designated day 0. On the
specified days after depilation, mice were killed, and each sample of
depilated skin was cut in half for analysis by immunohistochemistry and
RT-PCR, respectively. The stage of hair follicle growth was established
by the morphology of the hair follicles (24).
Immunohistochemistry
Animals were killed on days 0–10 after wounding or days
2.5–17.5 after depilation. Tissues were immediately fixed in 4%
paraformaldehyde in PBS (0.14 M NaCl, 2.7 mM
KCl, 4 mM
Na2HPO4, and 14.7
mM KH2PO4, pH
7.4) for 1–2 h at 4 C. Samples were then rinsed in PBS and stored in
70% ethanol until sectioned. For immunodetection of MRP/PLFs, 6-µm
sections were rehydrated and stained as previously described
(25) using a polyclonal rabbit anti-MRP/PLF serum
(89rb13a) or a preimmune serum from the same animal, each at a dilution
of 1:500. Primary antibody was detected using biotinylated goat
antirabbit IgG and horseradish peroxidase conjugated to avidin and was
visualized by a peroxidase substrate, diaminobenzidine
tetrahydrochloride (ABC kit, Vectastain, Vector Laboratories, Inc., Burlingame, CA). Samples were counterstained
with hematoxylin and eosin, dehydrated, and mounted with Permount
(Fisher Scientific, Pittsburgh, PA) with a coverslip on
top.
RNA isolation, RT-PCR, and diagnostic RT-PCR
Frozen tissue was pulverized in liquid nitrogen using a mortar
and pestle, and total RNA was isolated by using Tri-Reagent (Life Technologies, Inc., Gaithersburg, MD) according to the
manufacturer’s instructions. RT and RT-PCR were performed as
previously described (15, 21). For PCR of
Mrp/Plf cDNAs, the following primers were used: DE1;
5'-taagcctgggtaggactctgca-3' (+42 to +63); and UEV,
5'-catgatatttcagaagcagagcac-3' (+776 to +754). For G3pdh,
the primers used were 5'-tgtggatggcccctctggaaa-3' (+601 to +621) for
the upstream primer and 5'-gtttcttactccttggaggc-3' (+1053 to +1034) for
the downstream primer.
The diagnostic RT-PCR assay for the Mrp/Plfs is based on minor differences in the cDNA sequences of these closely related gene products that result in the presence or absence of restriction sites within the cDNA (15, 21). Amplified, radiolabeled fragments were digested with 1 U each of BsoFI and BstXI (New England Biolabs, Inc., Beverly, MA) at 55 C overnight in 50 mM NaCl, 10 mM MgCl2, 1 mM dithiothreitol, 100 µg/ml BSA, 10 mM Tris-HCl (pH 7.9 at 22 C). The radiolabeled and digested products were resolved by electrophoresis through 10% nondenaturing polyacrylamide gels. The gels were dried and exposed to film. Positive controls for identification of specific Mrp/Plfs were Plf1, Plf2, Mrp3, and Mrp4 cDNAs.
Keratinocyte isolation and culture
Newborn mouse keratinocytes were isolated as previously
described (26) with some minor modifications. Briefly,
newborn (days 3–4) mouse skin was removed and incubated overnight in
0.25% trypsin in HBSS without Ca2+ or
Mg2+ (Life Technologies, Inc.).
Epidermis was separated from dermis with tweezers, and then the dermis
was gently scraped with a razor blade to remove any keratinocytes that
remained with the epidermis. Epidermis was finely minced in Vogt’s
DMEM with high glucose (Life Technologies, Inc.)
containing 10% calf serum. Larger pieces were removed with tweezers.
The cells were collected by centrifugation at 500x g for 10
min, washed in HBSS, and resuspended in serum-free keratinocyte medium
(Life Technologies, Inc.) containing 25 µg/ml bovine
pituitary extract (Life Technologies, Inc.), 2.5 ng/ml
recombinant EGF (Life Technologies, Inc.), 100 U/ml
penicillin/streptomycin, and 90 µM
CaCl2. After being cultured overnight, unattached
cells were removed, and the medium was replaced with fresh medium as
before, but with 75 µM
CaCl2. Keratinocytes were cultured for up to 4
days with daily medium changes, and then the cells were cultured for an
additional 2 days without changing the medium. The medium was removed,
and fresh serum-free medium was added without pituitary extract, but
with the indicated growth factors. Total RNA was isolated after an
additional 14–17 h of culture.
Transgenic mice
Transgenic mice were produced by microinjection of a linearized
construct as described previously (27). The full-length
construct (CMV/Mrp3/sisGal/3U) contains the following elements in order
of 5' to 3': a 307-bp NruI-BanI fragment
containing the CMV-IE enhancer from pcDNA-3 (Invitrogen,
San Diego, CA), a 1514-bp XbaI to PstI fragment
of the Mrp3 promoter (-1450 to +64), the adenovirus/IgG
hybrid intron (28), the lacZ gene, and a
PvuII/EcoRI fragment including part of exon 5 of
the Mrp3 gene to the 3'-polyadenylase site (170 bp) and
about 600 bp 3' to the PvuII/EcoRI fragment in
the Mrp3 gene. As well, the full-length construct contained
the adjacent approximately 3000-bp EcoRI fragment that is 3'
to the PvuII/EcoRI 3'-end of the Mrp3
gene. Partial constructs were also used to prepare transgenic animals.
These partial constructs consisted of the same portions of the
transgene just described, but were lacking either the 3-kb
EcoRI fragment of the Mrp3 gene or the 5'
Mrp3 sequence from -42 to -1450 of the Mrp3
promoter had approximately 600 bp instead of approximately 3 kb of
the 3' Mrp3 untranslated region. To prepare the construct
for microinjection, the DNA was digested by NotI to
remove it from the vector (pckt17–2), resolved by electrophoresis
through a 0.8% agarose gel, and purified with GeneClean 101 (Bio
101, La Jolla, CA). The eluted DNA was precipitated with ethanol,
washed twice in 70% ethanol, and resuspended in 150
µM EDTA and 10 mM
Tris-HCl, pH 7.4.
Transgenic mice were identified by PCR analysis of DNA isolated from tail or ear tissue. ß-Galactosidase activity in wounds or hair follicles was detected as follows. Tissues were fixed for 40 min in 4% paraformaldehyde in PBS, then washed three times in PBS containing 0.01% Tween 20 and 0.02% sodium deoxycholate. The tissue was stained overnight at 30 C in 0.01% Tween 20, 0.02% sodium deoxycholate, 5 mM potassium ferricyanide, 5 mM potassium ferrocyanide, 2 mM MgCl2, 1 mg/ml X-gal, and 0.1 M sodium phosphate, pH 7.4.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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, top panel). Thirteen
of the 15 wounds examined between days 4 and 5.5 showed staining in the
wound area as in Fig. 1. Staining was never found in nonwounded tissue
(n = 8) or in wounds of 1 day (n = 2) or 2.5 days (n =
2). One in three wounds examined on day 3 were stained over the
keratinocytes. MRP/PLF staining is coincident with the period of
hyperproliferation of wound edge keratinocytes that occurs on about day
4. MRP/PLF staining was also less intense as the wound became
reepithelialized after day 7.5 (n = 6; data not shown). Basal
keratinocytes were not stained. Stain was occasionally found over the
outermost terminally differentiated keratinocytes. Often, keratinocytes
that stained for the MRP/PLFs were located along the hair follicles
near the wound. There was no stain using preimmune sera (Fig. 1, middle panel). None of the 19 wounds showed staining over
keratinocytes in areas removed from the wound as shown for the wound in
Fig 1 (bottom panel).
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Mrp3 is the major Mrp/Plf gene expressed during wound
healing
The presence of MRP/PLF protein in the suprabasal keratinocytes
suggested that one or more of the Mrp/Plf genes were turned
on in wounded tissue. Total RNA was extracted from wounds at different
times after wound healing and subjected to RT-PCR. G3pdh was
also amplified from the same cDNAs in parallel analyses to serve as
controls for sample quality. Mrp/Plf messenger RNA (mRNA)
was detected in wound tissue after 1 day of wounding and seemed to be
present at the highest levels at 2.5 days after wounding (Fig. 2A).
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was amplified
for an additional single round in the presence of
[32P]deoxy-CTP, digested with
Bsof1 and Bstx1, and separated on a nondenaturing
10% polyacrylamide gel. Standards for individual Mrp/Plf
forms were treated similarly and used as controls for the expected
fragments. As shown in Fig. 2B for day 2.5, Mrp3 makes up
most of the Mrp/Plf mRNA found in skin wounds. Similar
results were found for each day for which RNA could be detected by
RT-PCR.
Keratinocyte regulation of Mrp/Plf expression in response to growth
factors
To better understand which growth factors may be inducing
Mrp/Plf expression at the wound edge, newborn mouse
keratinocytes were isolated and treated with KGF (FGF7), EGF, or
TGF. Mrp/Plf gene expression, as measured by Northern
blot analysis, was increased in response to KGF, whereas EGF and TGF
had no effect on the level of Mrp/Plf mRNA (Fig. 3, A and B). As in the wound,
Mrp3 was the major form of Mrp/Plf expressed by
FGF-stimulated mouse keratinocytes, although some Plf1 was
also expressed (Fig. 3C). By comparison, 3T3 cells expressed mostly
Plf1.
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) and in two independent transgenic
mouse lines containing a CMV/MRP3/lacZ construct that
contained about 600 bp instead of about 3 kb of 3' Mrp3
untranslated region. One of the latter two lines also showed staining
in the panniculous carnosis. Both the location and the time course of
transgene expression were similar to those of endogenous
Mrp3 expression.
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). No staining was observed in tissue fixed immediately after
wounding (Fig. 4C). In a control transgenic mouse line containing the
CMV-IE enhancer but only 42 bp of the Mrp3 promoter,
lacZ was expressed constitutively throughout the skin and in
most other organs tested as well (not shown).
Presence of MRP/PLFs in the hair follicle
In the course of these studies it was noticed that some hair
follicles also stained for MRP/PLFs. The protein was detected by
immunocytochemistry using anti-MRP/PLF, but not with preimmune serum
(Fig. 5, A and B). MRP/PLF staining was
strongest in the outer root sheath of the hair follicle and was absent
from the bulb. The morphology of the follicles that were stained with
anti-MRP/PLF indicated that they were in the anagen stage of the hair
follicle cycle.
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, A, C, E, and H). Staining was
also seen in the outermost epidermal layers.
RNA isolated from nearby skin of the same animals was analyzed by
diagnostic RT-PCR (Fig. 6). Expression of
Mrp/Plfs was highest by day 17.5 (Fig. 6A), which
corresponds to late anagen (29). Mrp3 was the
predominantly expressed Mrp/Plf during normal hair follicle
cycling (Fig. 6B). Smaller proportions of Plf1 and
Mrp4 were also expressed.
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). Staining in the more
external elements of the hair follicles was generally darker and more
consistent than staining near the bulb region. This could have been due
to limitations in the penetration of the X-gal through the tissues.
Consequently, the distribution of ß-galactosidase expression was
also determined in hair follicles that had been plucked from the animal
before staining (Fig. 7B).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Mrp3 gene expression starts soon after wounding, although the MRP3 protein is not detected by immunohistochemistry until it has accumulated to high levels 4–5 days after wounding. The increase in Mrp3 gene expression revealed by RT-PCR begins early in the inflammatory stage and continues through the granulation stage of wound healing, the latter being the period of keratinocyte proliferation and the reepithelialization phase of wound healing (2).
KGF, a potent keratinocyte mitogen (4), increases Mrp3 expression in keratinocytes in culture. In vivo, dominant negative KGF receptors cause severe defects in wound healing (30), whereas KGF ligand knockouts show normal wound healing, but have abnormal coats (8). These results suggest that signaling through KGF receptors is crucial for wound healing, but the KGF ligand itself is not essential. This result is consistent with the observation that several members of the FGF family interact with Fgfr2, the KGF receptor.
Neither EGF nor TGF increased Mrp/Plf expression by
keratinocytes, even though these are mitogens for keratinocytes and
stimulate Mrp/Plf expression in 3T3 cells (10).
Here it is relevant that Plf1 is the major
Mrp/Plf gene expressed in 3T3 cells and the predominantly
expressed gene in keratinocytes is Mrp3. The Mrp3
promoter, but not the Plf1 promoter, is stimulated by FGF in
3T3 cells (31).
MRP3 was not detected in keratinocytes found at the wound surface, which are believed to be migrating across the wound. In humans, the migrating keratinocytes display the highest level of immunostaining for the cleaved and activated form of TGFß (32). Mrp/Plf expression by 3T3 cells is inhibited by TGFß (12). The results presented here showing that 3T3 cells express mostly Plf1 suggest that these previous studies demonstrated that TGFß inhibits the expression of Plf1. In 3T3 cells stably transfected with 2 kb of the Mrp3 promoter upstream from a chloramphenicol acetyltransferase reporter gene, TGFß also inhibited the Mrp3 promoter activity (Mohideen, M. A. K., and M. Nilsen-Hamilton, unpublished observations). Thus, Mrp3 expression may be suppressed by TGFß in migrating keratinocytes.
Although cultured keratinocytes are not physiologically equivalent to wounded skin, the regulation of Mrp/Plfs in response to growth factors may be similar to that in vivo. KGF is highly expressed by the dermis from 24 h after wound healing through at least 7 days (1). Mrp3 is expressed over this same period in suprabasal keratinocytes at the wound margins. During wound healing, proliferation of the underlying basal layer results in a greatly thickened layer of suprabasal keratinocytes. Although mitotic figures are evident in the suprabasal layer, the majority of cell proliferation in the wound is in basal keratinocytes. MRP3 might be part of a positive feedback mechanism by which the suprabasal cells stimulate further proliferation of the cells in the underlying basal layer. This mechanism would parallel that of PLF1, a growth factor for primary uterine cells (20). Because the mature forms of MRP3 and PLF1 are 99% identical, with a variation in only 2 of 195 amino acids, it is presumed that these proteins have the same functions. This assumption has not yet been verified.
PLF1 signals through two different receptor types: a unique MRP/PLF receptor (20) and the insulin-like growth factor II (IGF-II)/mannose-6-phosphate receptor (33, 34). In sheep, IGF-II receptors are expressed in the germinal matrix, with peak expression during late anagen/early catagen, and in the dermal papilla, with peak expression during telogen (35). If the IGF-II receptor is similarly expressed in the mouse, then the cells expressing these receptors are possible targets for the MRP/PLFs that are expressed in late anagen.
The FGF family stimulates proliferation and angiogenesis and is involved in cutaneous wound healing. Expression of a dominant negative FGF7 receptor in the skin of mice delays wound healing (5), and the application of bFGF enhances wound healing in healing-impaired db/db mice (6). Some FGFs are also produced in hair follicles; Fgf5 and Fgf7 mRNAs are present in the outer root sheath during anagen IV (7, 36). mRNAs encoding several FGF receptors are also present in the hair follicle during anagen: Fgfr1 mRNA in the dermal papilla, Fgfr2 RNA in hair matrix cells near the dermal papilla, Fgfr3 mRNA in precuticle cells in the periphery of the hair bulb, and Fgfr4 RNA in cells in the periphery of the hair bulb and the inner and outer root sheath in the lower half of the follicle neck. These FGFs and their receptors are likely to be active after the period of follicle growth, because proliferative cells are found in the outer root sheath during catagen and telogen (37). KGF is specific for Fgfr2 (38), but Fgfr4 is expressed by the outer root sheath cells. Thus, it is possible that an FGF other than KGF stimulates Mrp/Plf expression in these cells.
Expression of Mrp/Plf in the skin was confined to the wound keratinocytes and epithelial cells of the outer root sheath cells of the hair follicle. In these cells, Mrp3 was the major form expressed. Mrp3 expression was also observed in skin containing hair follicles in late anagen, where Plf1 and Mrp4 were also found in relatively smaller amounts. The expression of small proportions of Plf1 and Mrp4 in hair follicles and not in healing skin could reflect the different mouse strains used in the wound healing (FVB) and hair cycle (C57/BL6xCF-1 crosses) studies. However, we did not observe differences in Mrp/Plf types expressed in placental tissues from CF-1 and BALB/c mice (15). Recently, we also observed the expression of predominantly Plf1 in stomach (unpublished) and Plf1 and Mrp3 in small intestine (15), whereas Mrp4 is constitutively expressed in skin of the adult tail (15). Thus, mice seem to have evolved mechanisms to express different Mrp/Plf forms in different epithelial tissues.
Transgenic mice containing a CMV/MRP3/lacZ transgene expressed ß-galactosidase in the wound and hair follicles in the same cellular locations and with the same time course as seen by RT-PCR for endogenous mRNA expression and by immunocytochemistry for MRP/PLF protein localization. In these studies the presence of the CMV-IE enhancer seemed to increase expression from the Mrp3 promoter. In other studies, the CMV-IE enhancer did not efficiently increase transgene expression in the skin from the CMV promoter (39). However, the CMV-IE enhancer in combination with the chicken ß-actin promoter drove ß-galactosidase transgene expression strongly in many locations in the skin, with the highest expression observed in the sebaceous gland, epidermis, suprabasal and basal cells of the epidermis, and arrector pili muscle. Expression was not high in the outer root sheath. Thus, the promoter (CMV or ß-actin), rather than the CMV-IE enhancer, determines the pattern of expression of the transgene (39). We show here a different expression pattern of the Mrp3 promoter in combination with the CMV-IE enhancer than previously reported for CMV-IE enhanced with the CMV promoter or with the ß-actin promoter. Although the presence of the CMV-IE enhancer increases the level of transgene expression from the Mrp3 promoter, the information necessary to determine spatial expression of Mrp3 in the wound and the hair follicle seems to be present in the 1514-bp proximal Mrp3 promoter. This transgenic construct also expressed specifically in the giant cells of the placenta during gestation, which is the major site of Mrp3 expression during development (Fassett, J. T., and M. Nilsen-Hamilton, in preparation).
If the functions of MRP/PLFs in the skin are similar to those proposed for MRP/PLFs during reproduction, then MRP3 might promote proliferation by way of the MRP/PLF receptor (20) and angiogenesis through the IGF-II receptor/mannose-6-phosphate (19).
The timing of Mrp3 expression during the late anagen stage of the hair follicle cycle is not consistent with an immediate effect of this growth factor on angiogenesis, because the perifollicular capillary bed regresses after anagen (40). However, although most cell division ceases in the hair follicle after anagen, there is some proliferation in the outer root sheath during telogen (37). Thus, the immediate role of MRP3 might be to stimulate outer root sheath cell proliferation at a time when most cell proliferation in the hair follicle has ceased. However, a highly glycosylated and very stable protein such as MRP3, produced and secreted late in the hair follicle cycle, might be adsorbed to the proteins in the extracellular matrix and then released at a later time by proteolysis or another means. Perhaps MRP3 is released directly before the anagen phase of the subsequent hair cycle when it could act as an angiogenic factor as well as a growth factor for the newly forming hair follicle.
In conclusion, we have shown that Mrp3 is expressed in keratinocytes during wound healing and in the outer root sheath of the late anagen hair follicle. Members of the FGF family are the most likely positive regulators of Mrp3 gene expression in the skin, whereas TGFß may be a negative regulator. Studies with transgenic mice suggest that the DNA elements necessary to direct Mrp3 expression in the wound and in the hair follicle are present in the DNA sequences flanking the Mrp3-coding sequence. On the basis of the current findings, we propose that MRP3, previously identified only in the placenta, may play a role during wound healing and in the hair follicle cycle as a growth factor and an angiogenesis factor.
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Acknowledgments |
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Footnotes |
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2 Current address: Department of Laboratory Medicine and Pathology,
7220 BSBe, University of Minnesota, Minneapolis, Minnesota 55455.
Received September 1, 2000.
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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