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Molecular and Cellular Biology, December 2001, p. 8336-8345, Vol. 21, No. 24
Department of Obstetrics and
Gynecology,1 Department of
Physiology,2 Howard Hughes Medical
Institute,3 and Department of
Pathology,4 The University of Michigan Medical
School, Ann Arbor, Michigan 48109
Received 31 August 2001/Accepted 10 September 2001
The fucose In mammals, the large number of
discrete cell surface glycan structures includes many that are
decorated with fucose (42). Fucose is found on these
molecules in direct linkage to some serine residues, for example, where
they may contribute to Notch-dependent intracellular signal
transduction events (3, 32). Fucose also decorates some
asparagine- and serine/threonine-linked glycans, by attachment in an
Cell surface fucosylated glycans are also implicated in reproductive
physiology. For example, Control of cell surface fucosylation in this context is mediated by
cycle-dependent modulation of Fucosylated glycans are also implicated in the maturation of sperm in
the rodent (30, 34). Fucosyltransferase activities, including To directly determine if Targeting constructs.
FUT1 and FUT2 genomic DNA clones were
isolated and mapped from a commercially available P1 genomic library
(strain 129P2/OlaHsd; Incyte Genomics, St. Louis, Mo.) as previously
described (9). Targeting vectors were derived from the
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.24.8336-8345.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Deficiency of Reproductive Tract
(1,2)Fucosylated Glycans and Normal Fertility in Mice with Targeted
Deletions of the FUT1 or FUT2
(1,2)Fucosyltransferase
Locus


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ABSTRACT
Top
Abstract
Introduction
Materials and Methods
Results and Discussion
References
(1
2) galactose
structure is expressed by
uterine epithelial cells in the mouse and has been implicated in
blastocyst adhesion events thought to be required for murine
implantation. Fuc
(1
2)Gal
moieties and cognate
fucosyltransferases are also expressed by epithelial cells of the male
reproductive tract and have been implicated in sperm maturation events
that may contribute to fertilization. To determine directly if
Fuc
(1
2)Gal
moieties are required for fertility, we have
generated strains of mice that are deficient in genes encoding FUT1 and
FUT2, a pair of GDP-L-fucose:
(1
4)-D-galactosyl-R
2-
-L-fucosyltransferase enzymes (EC 2.4.1.69)
responsible for Fuc
(1
2)Gal
synthesis and expression. FUT1 null
mice and FUT2 null mice develop normally and exhibit no gross
phenotypic abnormalities. The Fuc
(1
2)Gal
epitope is absent
from the uterine epithelia of FUT2 null mice and from the epithelia of
the epididymis of FUT1 null mice. Fully normal fertility is observed in
FUT1 null intercrosses and in FUT2 null intercrosses. These
observations indicate that Fuc
(1
2)Gal
moieties are not essential to blastocyst-uterine epithelial cell interactions required for implantation and are not required for sperm maturation events that
permit fertilization and that neither the FUT loci nor their cognate
fucosylated glycans are essential to normal development.
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INTRODUCTION
Top
Abstract
Introduction
Materials and Methods
Results and Discussion
References
(1,3) linkage. Subsets of the latter molecules contribute to
selectin-dependent leukocyte adhesion (45). Fucose has
also been described for the
(1,6) linkage exclusively on the
N-acetylglucosamine residue attached to asparagine on
N-linked glycans (31), though the function of this
modification remains unknown. Some of the major blood group antigens,
including the ABO and Lewis blood group antigens, also correspond to
fucosylated glycan epitopes (28). These are composed of
(1,4)-linked and/or
(1,2)-linked fucose, some additionally
modified by terminal galactose or N-acetylgalactosamine
moieties, and are displayed by glycoproteins and glycolipids on
erythrocytes and many types of epithelium. In the stomach, for example,
gastric epithelial cells can express the Lewis b antigen, an epitope
corresponding to an
(1,4)- and
(1,2)fucosylated glycan, which has
been assigned a role in the attachment and pathogenesis of
Helicobacter pylori infection (11). Interactions between microbes and fucosylated glycans on mammalian host
cells extend to the small intestine in rodents, where host-derived
(1,2)fucosylated glycans support the growth of and are in turn regulated by Bacteroides thetaiotaomicron (4).
In each of these contexts, expression of cell surface fucosylated
glycans is directed in part by one or more of the cognate
fucosyltransferases responsible for their synthesis (24,
25).
(1,3)-fucosylated glycans are associated
with the process of morula compaction (1, 13) and may
contribute to sperm-egg interactions in some species (7). There is substantial experimental support for the hypothesis that in
rodents,
(1,2)fucosylated glycans contribute to the process of
blastocyst attachment to the uterine epithelial wall in the context of
implantation (23). During the rodent reproductive cycle,
(1,2)fucosylated glycan expression by the uterine epithelium is
dynamically regulated, in concert with hormonal changes that account
for the physiology of the estrous cycle, at a time that correlates with
endometrial receptivity for blastocyst implantation (21,
22). Coculture of blastocysts with uterine epithelia supports
blastocyst attachment (27). Attachment is inferred to be
dependent on
(1,2)fucosylated glycans, since attachment is inhibited
by the addition of
(1,2)fucosylated glycoconjugates, but not by
control fucosylated glycans, and by monoclonal antibodies (MAbs)
specific for
(1,2)fucosylated epitopes (27).
Intrauterine injection of a MAb directed against the
(1,2)fucosylated
(1,3)fucosylated glycan Lewis Y inhibited
blastocyst implantation in a dose-dependent manner (50).
Similarly, this antibody, but not control antibodies, inhibited
implantation in an embryo transfer model and in a uterine epithelial
cell-blastocyst coculture (46). Furthermore,
fluoresceinated probes prepared from
(1,2)fucosylated glycans
localize to the mural trophectoderm on hatched blastocysts and thus
colocalize with the site of blastocyst attachment to the receptive
uterine wall (26, 48). Considered together, these
observations imply an important or even essential role for
(1,2)fucosylated glycans in the implantation process.
(1,2)fucosyltransferase activity in
association with estrogen and progesterone levels (47).
Dynamic control of fucosyltransferase activity is in turn apparently
controlled by the dynamic modulation of the level of transcripts
derived from one or more
(1,2)fucosyltransferase genes (9,
40). In the uterine epithelium, control of
(1,2)fucosylated glycan expression largely correlates with cycle-dependent modulation of
expression of the FUT2
(1,2)fucosyltransferase locus
(9). In oophorectomized mice, estrogen activates the
accumulation of uterine epithelial cell
(1,2)fucosyltransferase
activity and its mRNA, whereas progesterone inhibits accumulation
(19, 40).
(1,2)fucosyltransferase activities, are expressed in the
rodent seminiferous tubules and epididymis (37, 38). A gradient of fucosyltransferase activity exists from the caput epididymis to the cauda epididymis (6, 34, 36) and is
apparently elaborated by the epithelial cells that line the epididymis.
This gradient aligns with the gradient of expression of the FUT1 locus observed by in situ hybridization in the mouse epididymal epithelia (8). The gradient of fucosyltransferase expression
parallels the apparent acquisition by spermatozoa of cell surface
(1,2)fucosylated glycans and correlates with acquisition of the
ability to fertilize that occurs during passage of spermatozoa through
the epididymis in the mouse (5, 43).
(1,2)Fucosylated
glycans may also be involved in sperm capacitation. Incubation of
spermatozoa from the cauda epididymis of mice with exogenous fucose
displaces a decapacitation factor, accelerating capacitation, while
incubation with the
(1,2)fucose-specific lectin Ulex
europaeus agglutinin-I (UEA-I) binds to the postacrosomal region
and blocks decapacitation factor reassociation (14). These
observations suggest an important or perhaps essential role for
epididymal
(1,2)fucosylation events in fertility.
(1,2)fucosylated glycans contribute
essentially to the blastocyst implantation events or sperm maturation process discussed above, and to begin to define the functions of cell
surface
(1,2)fucosylated glycans and their fucosyltransferases in
mammalian physiology, we carried out the construction and initial characterization of strains of mice with induced null mutations in
either the FUT2 locus or the FUT1 locus.
Homozygously FUT2 null mice are viable, appear healthy, no longer
exhibit the wild-type expression pattern of
(1,2)fucosylated glycans
in the uterine epithelium, and are fertile. Homozygously FUT1 null mice
are also viable and healthy, are deficient in epididymal cell surface
(1,2)fucosylated glycans expressed by wild-type mice, yet are also
fertile. These observations imply that
(1,2)fucosylated glycans play
nonessential roles in blastocyst implantation or sperm function in mice.
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MATERIALS AND METHODS
Top
Abstract
Introduction
Materials and Methods
Results and Discussion
References
-galactoside-containing nucleus-localizing plasmid pnlacF
(49). An existing SacI site within the 5'
polylinker site of pnlacF was modified into a NotI restriction site by utilizing two overlapping 15-mer oligonucleotides: 5'-CGC GGC CGC AGA GCT-3' and 5'-CTG CGG CCG
CGA GCT-3' (NotI site is underlined; overhangs for
ligation into SacI at the 3' end). The 15-mer
oligonucleotides were heated together to 65°C, cooled, ligated with
partially SacI-digested full-length pnlacF vector (6.3 kb),
and electroporated (Gene Pulser; Bio-Rad Laboratories) into
Escherichia coli JM109 (Promega Corp.), and blue colonies were isolated by blue-white selection on agar plates containing X-Gal
(5'-bromo-4-chloro-3-indolyl-
-D-galactopyranoside;
Roche Molecular Biochemicals). Insertion of the new NotI
site maintained in-frame translation of the lacZ coding
sequence and was confirmed by DNA sequencing. The resulting vector,
pnlacF NotI, was modified by ligation with a
PGK-neomycin resistance cassette (44) into an
EcoRI site in the 3' polylinker sequence of partially
digested full-length pnlacF. Orientation of the neomycin cassette in
the resulting 7.9-kb vector (pnlacF NotI Neo) was determined
by sequencing from the 3' end using the M13 forward sequencing primer
and from the opposite end using a 19-mer, 5'-TTG ACT ACC AAG CCA CCT
G-3', from the vector sequence within the 3' pnlacF polylinker.
Oligonucleotides were designed using the program MacVector (Oxford
Molecular Group) and synthesized on Applied Biosystems DNA synthesizers
in the University of Michigan DNA Synthesis Core. All sequencing was performed in the University of Michigan DNA Sequencing Core Facility on
Applied Biosystems DNA sequencers.
ES cell manipulation.
A mouse ES cell line (designated Pat5)
was prepared from mouse strain 129X1/SvJ (stock no. 000691; Jackson
Laboratory) according to a published immunosurgery protocol
(41). Briefly, blastocysts obtained by mating 129X1/SvJ
mice were subjected to immunosurgery to eliminate trophectoderm cells,
as described previously (41). The inner cell mass cells
were established in tissue culture on feeder cells. Primary mouse
embryo fibroblasts (MEF) were prepared from mice transgenic for the
neo gene and used as feeder cells. ES cells were cultured in
high-glucose Dulbecco's minimal essential medium supplemented with
15% fetal bovine serum, 1 µM
-mercaptoethanol, 4 mM glutamine, 50 IU of penicillin per ml, 50 µg of streptomycin per ml, and 1,000 U of
recombinant leukemia inhibitory factor (ESGRO; Chemicon International,
Inc) per ml. In addition, R1 ES cells were independently used for
FUT1 and FUT2 targeting (33).
80°C.
The cells in the third set of plates were grown to high density and
split between two 96-well plates. The cells in the final duplicate
plates were grown to high density, and genomic DNA was extracted
(35) for Southern blot analysis. Clones that were positive
in the initial screening were expanded, and their genotypes were
confirmed by additional Southern blot analyses.
Southern blot screening of targeted ES cells. Southern blot probes derived from positions 5' and 3' to the borders of the targeting constructs were used in primary and secondary screening of ES colonies. For FUT2, a 5' 400-bp BamHI/KpnI probe and 3' 390-bp KpnI/SacI probe were derived from genomic clones previously mapped 5' and 3' to FUT2 (9). For FUT1, PCR was used to generate a 3' 355-bp probe (25-mer forward primer, 5'-CGC TTG TCT ATT TAG GAC AGG AAC C-3'; 25-mer reverse primer, 5'-GAT TCA GGA GCC AGA ACT GAT TCT C-3') and a 5' 238-bp probe (22-mer forward primer, 5'-GTG GAA ACC CAA AAA GAA ACA G-3'; 20-mer reverse primer, 5'-CGT CTG CCT CAG AAG GAC TC-3). These probes and Southern blot analyses identified four homologously recombinant FUT2-LacZ clones and more than 12 homologously recombinant FUT1-LacZ clones.
Blastocyst injection of homologously targeted ES cells. Clones with the modal number of 40 chromosomes were injected into host C57BL/6J blastocysts by the Transgenic Animal Model Core using standard protocols (2). The resulting male ES cell-mouse chimeras were crossed with wild-type female C57BL/6J mice to obtain germ line transmission of the targeted alleles. Two FUT2-LacZ clones and four FUT1-LacZ clones yielded germ line transmission.
PCR genotyping of progeny from chimeric mice. Southern blotting and PCR genotyping were used to genotype the first 100 progeny derived from FUT2-LacZ and FUT1-LacZ germ line-transmitting chimeric mice. The Southern blot probes are described above. Tail DNA was purified by proteinase K digestion, NaCl precipitation, and spooling on glass pipettes (29). PCR genotyping of the FUT2-LacZ locus used a forward primer whose sequence is present in both the wild-type and the FUT2-LacZ allele (21-mer primer a, 5'-CCT GCC ATG CTT TCT TTC CTG-3'). Two reverse primers were used with primer a to discriminate between the wild-type and the FUT2-LacZ allele. Reverse primer b corresponds to a sequence in the wild-type allele (23-mer, 5'-ATT CCT TCT CTG ACA GGG TTT GG-3'). Reverse primer c corresponds to the lacZ sequence in the FUT2-LacZ allele (20-mer, 5'-TGG GTA ACG CCA GGG TTT TC-3'). Primer pairs a and b yield a 154-bp fragment from the wild-type allele. Primer pairs a and c yield a 191-bp fragment from the FUT2-LacZ null allele.
PCR genotyping of the FUT1-LacZ locus used a forward primer whose sequence is present in the wild-type and the FUT1-LacZ allele (24-mer primer d, 5'-CGG TGG CTT AAT CTG TGT GTC TTC-3'). Two reverse primers were used with primer d to discriminate between the wild-type and the FUT1-LacZ allele. Reverse primer e corresponds to the wild-type sequence in both the wild-type and FUT1-LacZ alleles (23-mer, 5'-GCA ATG GAT GAG GTA GGC ATA CC-3'). Reverse primer f corresponds to the lacZ sequence in the FUT1-LacZ allele (24-mer, 5'-CCA GTC ACG ACG TTG TAA AAC GAC-3'). Primer pairs d and e yield a 239-bp fragment from the wild-type allele. Primer pairs d and f yield a 130-bp fragment from the FUT1-LacZ null allele. The DNA template for PCR genotyping used either 0.75 µg of purified tail DNA as described above or 2-µl aliquots of a crude proteinase K digestion of mouse tails: the distal 5 mm of a tail tip biopsy sample was digested overnight in 50 µl of digestion buffer (10 mM Tris-HCl [pH 9.0], 50 mM KCl, 0.1% Triton X-100, 0.4 mg of proteinase K/ml) at 56°C and then heated to 94°C for 10 min to denature proteinase K prior to PCR. All PCRs used primers at 0.4 µM (except primer c, which was used at 0.8 µM), 1.5 mM MgCl2, Taq polymerase (Life Technologies, Gibco BRL), and buffer conditions supplied by the manufacturer. Annealing was done at 55°C for FUT2 and 60°C for FUT1. PCR fragments were fractionated though 2% agarose gels containing 0.5% NuSieve agarose (FMC BioProducts).Lectin histochemistry.
The
(1,2)fucose-specific lectin
UEA-I conjugated to biotin (EY Laboratories Inc.) and blood group MAbs
BG-4 and BG-1 (Signet Pathology Systems Inc.) were used in automated
immunoperoxidase staining. BG-4 is specific for type I H antigen; BG-1
is specific for nonfucosylated type I lacto-N-biose
disaccharide. Adult wild-type, FUT2 null, and FUT1 null female mice
were monitored through the estrous cycle by vaginal washings. Uteri
from mice in estrus were fixed in 10% buffered formalin at 4°C
overnight, embedded in paraffin, and processed for
immunohistochemistry. Epididymides from adult male mice were processed
in the same manner. Immunohistochemistry was done in the University of
Michigan Comprehensive Cancer Center Research Histology and
Immunoperoxidase Laboratory using a Dako Corp. autostainer
immunostaining system and the manufacture's protocol. No antigen
retrieval step was necessary. With mouse MAbs (BG-4 and BG-1),
preincubation with an immunoglobulin blocking reagent was performed
according to the manufacturer's protocol (Mouse-on-Mouse
immunodetection kit peroxidase; Vector Laboratories). Control sections
processed for immunohistochemistry with all reagents except the primary
reagents showed virtually no staining.
Breeding of F1 and F2 generations.
Four male-female F1 FUT1 heterozygous (+/
) and
FUT2 heterozygous (+/
) pairs were mated. In excess of 160 progeny
were sexed and genotyped to ascertain any sex ratio distortion or
decreased fetal or postnatal viability as a function of FUT1 or FUT2
genotype. For the F2 crosses, gestational
duration and enumeration of litter size were done with male-female
pairs that were continuously housed. Progeny were immediately removed
after birth to ensure that the female would be continuously fertile.
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RESULTS AND DISCUSSION |
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Construction of mice with targeted deletions of the FUT2 and FUT1
(1,2)fucosyltransferase genes.
A targeting vector for
homologous recombination-mediated inactivation of the FUT2
locus was constructed from a mouse FUT2 genomic fragment
(Fig. 1). This vector deletes the
majority of the single coding exon of the FUT2 locus,
including all of the part of the exon that corresponds to the enzyme's
catalytic domain (9). The E. coli
-galactosidase coding sequence was fused in frame to the
amino-terminal six residues proximal to the transmembrane segment of
FUT2, for eventual use in immunohistochemical detection of the cell
type-specific expression patterns of this locus. Chimeric males
obtained from blastocyst injection of two independent heterozygous ES
clones derived with this construct gave rise to heterozygous progeny
when crossed with wild-type females. Heterozygous progeny were
intercrossed to generate mice homozygous for the FUT2 locus. A Mendelian distribution of genotypes was observed among the progeny, males and females were present in equal numbers regardless of genotype,
and no gross behavioral or morphological abnormalities were observed
among heterozygous or homozygous null progeny.
|
-galactosidase coding sequence in frame to the amino-terminal five residues proximal to the transmembrane segment
of FUT1 (Fig. 2). Chimeric males obtained
from blastocyst injection of four independent heterozygous ES clones
derived with this construct gave rise to heterozygous progeny when
crossed with wild-type females. Heterozygous progeny were intercrossed to generate mice homozygous for the FUT1 locus. The
genotypes of the progeny were Mendelian in distribution, males and
females were present in equal numbers in all genotypes, and no obvious behavioral or morphological abnormalities were observed in any of the
progeny.
|
Expression of
(1,2)fucosylated glycans in uterine epithelia
requires FUT2 and is exclusive of a contribution by FUT1.
Hybridization in situ and biochemical analyses are generally if not
completely consistent with an assignment to the FUT2 locus, and not the FUT1 locus, in controlling expression of
(1,2)fucosylated glycans in uterine epithelium during the estrous
cycle (9, 40). To confirm these assignments, and to verify
that deletion of the FUT2 locus abolishes expression of
(1,2)fucosylated glycans in this context, expression of H antigen
was assessed on uterine epithelia in FUT2
/
mice, FUT1
/
mice, and wild-type controls
(Fig. 3) at estrus, where, in wild-type mice, expression of these glycans is prominent (22, 47)
and implicated in implantation (21, 27). H antigen is
clearly evident on wild-type epithelial cells, as detected with a
lectin with specificity for
(1,2)fucosylated glycans (UEA-I), and
with a MAb with specificity for type I H blood group structure (Fig. 3A). H-reactive glycans localize primarily to the glycocalyx on the
luminal side of the cells, where they are eligible for interaction with
blastocysts susceptible to implantation. By contrast, the uterine
epithelium in FUT2
/
mice is devoid of
detectable H structures when probed with these reagents. Deletion of
(1,2)fucosylated glycans in the FUT2
/
uterine epithelia is not consequent to deletion of glycans that may
serve as H-antigen precursors (28), since such unmodified type I glycans continue to be expressed by these cells (Fig. 3B). Small
amounts of FUT1 transcripts are detected in the mouse uterus at estrus, though in situ hybridization analyses do not clearly indicate that they are localized to the uterine epithelia
(9). These transcripts and their cognate
fucosyltransferase do not detectably contribute to
(1,2)fucosylated
glycans in uterine epithelia, since such glycans are fully deleted in
FUT2 null epithelia. These observations confirm that the FUT2 mutant
allele is null, definitively assign the FUT2 locus to the
control of
(1,2)fucosylated glycan expression in uterine epithelia,
and indicate that FUT2-dependent control of
(1,2)fucosylated glycans in uterine epithelia is exclusive of a
contribution by the FUT1 locus, since such glycans are fully deleted in FUT2 null epithelia yet are retained in the
FUT1
/
epithelia (Fig. 3).
|
Expression of
(1,2)fucosylated glycans in epididymal epithelia
requires FUT1 and is exclusive of a contribution by FUT2.
In the
murine epididymis, a gradient of fucosyltransferase expression
associated with spermatozoa increases from the caput, near the
seminiferous tubules, to the cauda, near the junction with the vas
deferens (6, 34, 36). This gradient parallels the
acquisition by spermatozoa of
(1,2)fucosylated glycans, correlates with acquisition by spermatozoa of the ability to fertilize (5, 43), and implies a requirement for these epididymis-associated
(1,2)fucosylation events in fertility. In situ hybridization analyses define a gradient of expression of FUT1 transcripts
in the epithelia along the length of the epididymis (8)
but do not detect FUT2 transcripts in this organ, implying
that the FUT1 locus controls epididymal
(1,2)fucosylation
events associated with maturation of spermatozoa. To confirm these
assignments and to verify that deletion of the FUT1 locus
disables expression of
(1,2)fucosylated glycans, H-antigen
expression was assessed on the epithelia of the proximal and mid-caput
portions of the epididymis and on the corpus of the epididymis in
FUT1
/
mice, FUT2
/
mice, and wild-type controls (Fig.
4). In wild-type mice,
H antigen, detected with the lectin UEA-I, is prominently expressed in
the mid-caput of the epididymis but is absent from the proximal segment of the organ (Fig. 4). In the mid-caput, H antigen localizes to the
luminal surface of the epididymal epithelia and is also associated with
spermatozoa and molecules within the tubules.
|
/
mice are indistinguishable from
wild-type mice with respect to the density of H-antigen expression on
epididymal epithelia and in the luminal contents, to the gradient of H
expression along the length of the epididymis, to the extent and
location of intracellular expression in mid-caput epithelia, and to the
overall microscopic morphology of the tubules (Fig. 4). These
observations indicate that FUT2 is not required for H expression in
these contexts or for the organization or structural integrity of the
tissue. By contrast, the epididymal epithelia in
FUT1
/
mice are devoid of detectable H
structures. This observation demonstrates that the FUT1
mutant allele is null and assigns the FUT1 locus, exclusive
of FUT2, to the control of
(1,2)fucosylated glycan
expression in the epididymis. Tubular and epithelial morphology and the
overall organization of the epididymal structures are normal in
FUT1
/
mice, indicating that FUT1 is not
required for the development of this tissue.
Northern blot analyses identify transcripts derived from the
SEC1 locus in testes and epididymis (9). The
SEC1 locus is predicted to encode a polypeptide with
substantial primary sequence similarity with FUT1 and FUT2, directs
low-level expression of
(1,2)fucosylated glycans in transfected
mammalian cells (9), and is therefore a candidate for
control of expression of
(1,2)fucosylated glycans in the epididymis.
However, SEC1 does not contribute in this context, since
(1,2)fucosylated epitopes are fully deleted from the glycans in the
FUT2 null epididymis.
Uterine epithelial
(1,2)fucosylated glycans are dispensable for
fertility.
Blastocyst attachment to uterine epithelia in vitro and
blastocyst implantation in vivo are inhibited by blockade of
(1,2)fucosylated glycans corresponding to the H and Lewis Y epitopes
(27, 46, 50). Blockade correlates with binding of
(1,2)fucosylated glycans to the mural trophectoderm on hatched
blastocysts, the site of blastocyst attachment to the receptive uterine
wall (26, 48). These observations, together with
cycle-dependent expression if
(1,2)fucosylated glycans by the
uterine epithelia, have suggested an essential role for uterine
(1,2)fucosylated glycan-dependent adhesive interactions in
fertility. To directly examine this issue, fertility was assessed in
FUT2 null mice, whose uterine epithelia are genetically deficient in
expression of
(1,2)fucosylated glycans. In intercrosses of FUT2 null
adults, elapsed time between the first day when a male is housed with a
receptive female and the day of birth (mean ± standard deviation,
26.6 ± 5.8 days) does not differ from elapsed time to birth in
wild-type intercrosses (25.7 ± 5.2 days) (Fig.
5). FUT2 null intercrosses also yield litter sizes (8.1 ± 1.6 pups) equivalent to the sizes of litters born in wild-type intercrosses (8.8 ± 1.6 pups). These
observations indicate that FUT2 null females are as competent as
wild-type females in initiating and sustaining pregnancy and excludes a requirement for uterine epithelial cell surface
(1,2)fucosylated glycans in the support of blastocyst adhesion or implantation or in the
maintenance of pregnancy. These observations also show that the
FUT2 locus is dispensable for fertility in males.
|
Normal fertility in the absence of epididymal
(1,2)fucosylated
glycans.
During passage from the caput to the cauda of the
epididymis, spermatozoa acquire
(1,2)fucosylated glycans during a
maturational translocation from the testes that is associated with
acquisition of competence for fertility (5, 43). To
determine if epididymal acquisition of
(1,2)fucosylated glycans is a
prerequisite for the fertilization competence of spermatozoa, fertility
was assessed in FUT1 null mice, wherein
(1,2)fucosylated glycans are
absent from the epididymal epithelia. In FUT1 null intercrosses,
elapsed time to birth (26.0 ± 4.8 days) is equivalent to that in
wild-type intercrosses (Fig. 5), as is the average litter size
(8.9 ± 1.7 pups) (Fig. 5). FUT1 null males are therefore as
fertile as wild-type males, excluding a requirement for FUT1-dependent
epididymal fucosylation events in the spermatozoan maturation process.
These observations also exclude a requirement for FUT1-dependent
fucosylation in postcoital fertilization events, where fucosylated
glycans have been implicated in sperm capacitation (14),
and exclude a requirement for FUT1 in female fertility.
(1,2)fucosylated glycans elaborated by FUT1 and FUT2 but leave open
the possibility that such glycans contribute to other functions in the
reproductive tract, including protection from pathogens. The
lineage-restricted expression of FUT1 and FUT2 characteristic of the
reproductive tract extends to other tissues in the mouse, inferring
potential functions for their cognate glycans in other biological
contexts. Aside from the uterus, expression of the FUT2
locus is restricted to the stomach and colon among the major organs in
an adult mouse (9). Extraepididymal expression of the
FUT1 locus has also been assigned to the stomach and colon; in those locales, the two corresponding fucosyltransferases may contribute to host-microbe interactions that involve fucosylated glycans (18). Efforts are in progress with
FUT1
/
and FUT2
/
mice to determine if the absence of
(1,2)fucosylation in the gastrointestinal tract modulates their susceptibility to microbial symbiosis, commensalism, or pathogenicity and to more carefully define
expression patterns in these contexts using the
-galactosidase reporter installed in each locus.
These mice are also being used to determine if thymus-specific
expression of FUT1 (8) controls expression of
(1,2)fucosylated glycans displayed by the medullary epithelial cells
in this organ (12) and to identify functional correlates
for such expression. Similar considerations apply, for example, to the
intestinal M cell, an H-antigen-positive epithelial cell that overlies
mucosa-associated lymphoid tissues (17), to the
(1,2)fucosylated olfactory epithelium (10), to rare
(1,2)fucosylated enteroendocrine cells of the gastrointestinal tract
(15, 16), and to other cell types revealing restricted
expression of
(1,2)fucosylated glycans in development and
differentiation (39).
| |
ACKNOWLEDGMENTS |
|---|
This work was supported by a fellowship grant from the Reproductive Scientist Development Program and NIH K08 HD01195 (S.E.D), P01 CA71932 (J.B.L), University of Michigan Cancer Research Committee John S. and Suzanne C. Munn Endowed Research Fund (S.E.D.), and University of Michigan Phoenix Memorial Laboratory Michigan Memorial-Phoenix Project no. 856 (S.E.D.). J.B.L. is an Investigator of the Howard Hughes Medical Institute.
We are grateful to the University of Michigan Transgenic Animal Core (L. Samuelson, S. Camper, E. Hughes, M. Berand, and M. Van Keuren), DNA Sequencing Core (R. Lyons, S. Genik, and C. Esposito), DNA Synthesis Core (C. Wong), and Comprehensive Cancer Center Research Histology and Immunoperoxidase Laboratory (M. Rubin, M. LeBlanc, and N. McAnsh). We acknowledge R. Palmiter for plasmid pnlacF, T. Doetschman for mice transgenic for the neo gene, and J. Rossant and J. C. Roder for the R1 cell line made available through the Transgenic Animal Model Core.
| |
FOOTNOTES |
|---|
* Corresponding author. Mailing address: Department of Obstetrics and Gynecology, 6428 Medical Science Bldg. I, 1150 West Medical Center Dr., The University of Michigan, Ann Arbor, MI 48109-0617. Phone: (734) 647-9562. Fax: (734) 936-8617. E-mail: sedomino{at}med.umich.edu.
Present address: Henry Ford Hospital, Detroit, MI 48202.
Present address: Pfizer Global Research & Development, Ann Arbor,
MI 48105.
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