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Ultrastructural localization of lectin receptors in the preimplantation ovine embryo.

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THE ANATOMICAL RECORD 240:537-544 (1994)
Ultrastructural Localization of Lectin Receptors in the
Preimplant ation Ovine Embryo
P. DE PAZ, A.J. SANCHEZ, J.G. FERNANDEZ, C. GARCIA, C.A. CHAMORRO,
AND L. ANEL
Departamento de Biologia Celular y Anatomia (P.D.P., A.J.S., J.G.F., C.G., C.A.C.) and
Departamento de Patologia Animal (Sanidad) (L.A.), Facultad de Veterinaria,
Universidad de Leon, Leon, Spain
ABSTRACT
Background: Preimplantation development of mammalia is
characterized by cell surface changes functioning in intercellular communication and adhesion. The glycoconjugate role in cellular interactions has
been analysed for several groups but not in sheep embryos. The binding
patterns of eleven lectins during sheep preimplantation development were
investigated and the role of glycoconjugates in early development was discussed.
Methods: Ultrathin sections from preimplantation ovine embryos (3-7
days) were incubated with different colloidal gold conjugated lectins and
the frequency of gold particles on the cell membrane, some organelles, and
the zona pellucida was evaluated.
Results and Conclusions: We observed a higher staining of WGA, DBA,
and SBA lectins in the intercellular contact zone with respect to the free cell
surface of blastomeres during cleavage. This indicates that the N-acetyl
galactosamine and N-acetyl glucosamine residues may be involved in sheep
morula compaction. In contrast, the trophoblast cell displays an increase of
staining of some lectins previously identified during cleavage (LcH, WGA,
SBA, MPA, and PNA) on the free membrane, and a lack of sugar residues
in the intercellular surface. This polarization of the trophoblast cell surface
is not observed in the inner cell mass and could provide a mechanism for
differentiation within the blastocyst. Intracytoplasmic vesicles show a cytochemical identity with lysosomes in the blastocyst (abundant GlcNAc and
Man/Glc residues) that may reflect a functional relationship between both
organelles in an intracellular cycle. The zona pellucida presents abundant
GalNAc, GlcNAc, and Gal residues during preimplantation ovine development. 0 1994 Wiley-Liss, Inc.
Key words: Lectins, Sheep, Preimplantation embryo
The nature of the molecules present in the cell membrane and its more extrinsic component is of considerable interest because of the unique position of the cell
surface a t the interface between a cell and its external
environment. In particular it is important in the understanding of morphogenesis to characterize the
changes occurring in cell surface components during
development. In most instances, efforts have focussed
on the protein components, though it has been suspected for some time that cellular interactions are dependent upon complex carbohydrates. The critical role
of glycoconjugates in cellular interactions has been
clearly defined by different investigators (Gooi et al.,
1981; Sharon and Lis, 1989; Peacock et al., 1990;
Brandley, 1991).
Cell surface changes in cells and tissue including the
preimplantation mammalian embryo have been investigated with lectins (Lis and Sharon, 1986; Dealtry and
Sellens, 1987; Spicer and Schulte, 1992). The charac0 1994 WILEY-LISS, INC.
terization of the glycoconjugate composition of blastomeres during early development may provide clues
a s to the macromolecules functioning in intercellular
communication and changes in cell behavior (Shur,
1989; Fenderson and Eddy, 1990).
Early development of mammalian embryo is characterized primarily by a major morphological event
termed compaction that causes a major reorganization
among the cells of the morula. Compaction is a complex
process in which polarization of blastomeres occurs,
cell-cell contacts are maximized, and specialized junctions formed (Rastan el al., 1985; Wiley, 1988; Watson,
1992). This process is a prerequisite for blastocyst for-
Received February 1, 1994; accepted June 22, 1994.
Address reprint requests to Paulino De Paz, Departamento de Biologia Celular y Anatomia, Facultad de Veterinaria, Universidad de
Leon, 24071 Leon, Spain.
538
P. DE PAZ ET AL
TABLE 1. Description of the lectins used in this study and their specificities'
Lectin
Concanavalia
ensiformis
Abbreviation
ConA
Specificity'
Man a1,2 Man a1,2 Man >
Man a1,2 Man > a Man >
a Glc > a GlcNAc
con^.^
1:15
Sugar
(0.2 M)
D-Man
1:15
D-Man
1:lO
D-GlcNAc
Source
Sigma
Chemical
co. (St.
Louis, MO)
E-Y Laboratories
(San Mateo,
CAI
E-Y Laboratories
1:lO
D-GlcNAc
Lens culinaris
Lch
a Man > a Glc > a GlcNAc
Griffonia
simplicifolia 11
Triticum vulgare
GS-I1
a GlcNAc =
WGA
Dolichus biflorus
DBA
Glycine max
SBA
GlcNAc p1,4 GlcNAc
p1,4GlcNAc >
GlcNAc p1,4 GlcNAc >>
GlcNAc
GalNAc a1,3 GalNAc >
a GalNAc >> a Gal
a GalNAc = p GalNAc > a
Gal
GalNAc > Gal
Gal p1,3 GalNAc >
GaINH, > Gal
a-L-Fucosa
a-L-Fucosa
Maclura pomifera MPA
Arachis hypogaea PNA
Ulex europaeus I
Lotus
tetranoglo bus
Limulus
polyphemus
UEA-I
Lotus
LPA
13 GlcNAc
NeurGc a 2,3 GalNAc >
NeurAc a 2,6 GalNAc >
NeurAc = NeurGc
Diluent
Buffer
pH
0.01 M PBS
7-8
0.15 M NaCl
0.1 mM Ca2+
and Mn2+
0.05 M TRIS 7.2
0.15 M NaCl
0.01 M PBS
7.45
E-Y Laboratories
0.01 M PBS
7.45
1:lO
D-GalNAc E-Y Laboratories
0.01 M PBS
7.45
1:lO
D-GalNAc E-Y Laboratories
0.01 M PBS
7.45
1:lO
1:lO
D-Gal
D-Gal
E-Y Laboratories
E-Y Laboratories
0.01 M PBS
0.01 M PBS
7.45
7.45
1:lO
1:lO
L-FUC
L-FUC
E-Y Laboratories
E-Y Laboratories
0.01 M PBS
0.01 M PBS
7.45
7.45
NeurNAc
E-Y Laboratories
0.05 M T R I S
0.15 M NaCl
0.1 mM Ca'+
8
1:5
'For each lectin the dilution (Conc.),inhibiting sugar, and diluent solution are indicated. The buffers used are the ones recommended by the
commercial laboratories.
'After Goldstein and Poretz (1986).
3Referred to commercial solutions.
mation in which two distinct cell populations can be catheter. The embryos were classified morphologically
distinguished: the trophectoderm and the inner cell as excellent to poor according to Lidner and Wright
mass. There is abundant evidence that glycoconjugates (1983) and only those with a quality grade of 1 or 2
are involved in these processes (Gooi et al., 1981; Kim- were analyzed.
ber and Bagley, 1987; Bayna et al., 1988; Hathaway et
al., 1989; Bukers a t al., 1990).
L ectin Staining
In this paper we have investigated the binding pattern of 11 lectins during preimplantation development
The embryos were fixed with a mixture of formaldeof sheep embryos and discussed the role of glycoconju- hyde (4%) and glutaraldehyde (0.25%) in PBS for 1 hr
gates in early development.
a t 4°C and immersed in 0.5 M ammonium chloride for
another 30 min. After dehydration in a graded series of
MATERIALS AND METHODS
ethanol (30, 50, 70, 90, and 100%) a t decreasing temEmbryo Collection
peratures (0, -20, -30, -30, and -3O"C, respectively)
Adult Churra ewes were pretreated with fluoroge- the pieces were infiltrated and embedded in Lowicryl
stone acetate (FGA; Chronogest, Intervet, Holland) 30 K4M at -25°C for 24 h r and 20°C for 72 hr.
mg intravaginal pessaries for 12 days. Sixty hours beThe sections were then cut with glass knives on an
fore sponge removal donors were superovulated with ultratome LKB V and mounted on 150 mesh nickel
12 mg of follicle stimulating hormone-pituitary extract grids having a formvar film. Grids were preincubated
(FSH-P,Shering Corp., Kenilworth, NJ, USA) with the for 15 min on a drop of 0.5 M glycine in PBS and incufollowing dose: 4, 4,3, 3, 2, and 2 mglanimal at 12 hr bated on a drop of the gold labelled lectin for 6 hr in a
intervals. At the time of fifth dosage, 400 IU pregnant moist chamber a t room temperature according to Table
mare serum gonadotrophin (PMSG, Foligon, Intervet, 1. At the end of the labelling procedure the sections
Holland) were administered. Ewes were both naturally were washed with PBS, rinsed in doubly-distilled wamated and artificially inseminated 12-24 h r after the ter, and dried. The grids were stained with uranyl aconset of estrus.
etate and lead citrate.
The embryos were recovered surgically 3 to 7 days
The colloidal gold-conjugated lectins and the inhibafter sponge removal. The uterine horns or oviduct iting sugars used in this study are shown in Table 1.
were flushed with DPBS + 15% FCS using a Foley Preliminary studies with sugar a t different concentra-
539
LECTIN RECEPTORS IN EARLY OVINE EMBRYO
TABLE 2. Staining patterns (mean 2 s.d.) showed by the lectins used in this study in the different stages of
ovine Dreimdantation develoDment'
Cell membrane (uipm)
Cleavage
Lectin
ConA
LcH
GS-I1
Free
Interc
10 (2.1)
4 (2.4) 12 (2.6)
-
-
-
WGA 25(6.4) 42 (12.3)
DBA
10 (2) 35 (5.9)
SBA
8 (2.9) 40 (8)
MPA
4(0.5) 4 (0.3)
PNA
2(0.5) 4 (0.4)
UEA-I
611.6)
Lotus
LPA
-
Organelles (uipm2)
BICM
Cleavage
B Troph
BICM
Zona pellucida ( d p m 2 )
Free
Interc Interc
Vesic
Lysos
Vesic
Lysos
Vesic
Lysos
Cleav
Blast
8 (2.1) 6 (1.9) 72 (17.9) 18 (3.8) 80 (26.1) 14 (6.4) 78 (13.3) 16 (9.2)
32 (11.3)
30 (3.7)
69(11.2) 4(1.4) 4(1.5) 26(9.1)
29 (13.6) 26 (4.4)
B Troph
-
-
-
-
2 (0.5) 8(1.4) 86(18.3)
-
-
-
-
-
-
18 (2)
210 (10)
34 (2)
40 (4)
36 (4.2)
40 (3.3)
20 (8)
230 (16)
14 (3.1)
6 (2)
28 (6.8)
34 (2.3)
-
-
-
-
6(1.2)
6(1.1)
4(0.5)
4(1.6)
-
-
-
-
-
-
4 (1.4)
4(1.2)
4(1.3)
8(1.1)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
16(5.2)
-
-
-
-
-
-
-
-
-
-
-
~
32 (11.8) 120 (13)
28 (13.5) 140 (7.2)
74(15.9)
8 (3.4)
37 (7.2)
30(6)
28(4.1)
8(0.5)
-
'These data refer to the free and intercellular (Interc) membrane (colloidal gold particlesipm), the cell organelles (gold colloidal particlesipm'),
and the zona pellucida (gold colloidal particlesipm'). > 100 particlesiu = very heavy; 50-100 = heavy; 25-50 = light; < 25 = sparse;-= 0.
Vesic = intracytoplasmic vesicles; Lysos = lysosomes; Cleav = cleavage; B Troph = blastocyst trophectoderm; BICM = blastocyst inner cell
mass; Blast = blastocyst.
tions were carried out in order to assess the carbohydrate specificity of the lectin to the embryonic cells.
In the whole series of experiments we used grids with
sections from the same embryo a s a control for the specific binding of the lectins. These sections were incubated with the lectin-gold complex previously mixed
with the corresponding specific sugar for 1 h r before
use (see Table 1).
Six embryos from each stage were used, six ultrathin
sections per embryo were incubated with lectin and six
micrographs per section were obtained by random sampling.
The frequency of gold particles per square micron
(organelle and zona pellucida) or per micron (plasma
membrane) was determined by counting on the electron micrographs. A double square lattice ((264) is superimposed on each micrograph to estimate the area of
cellular organelles and the length of membrane profiles (Weibel, 1979). The gold particle number of each
structure was counted and this count was standardised
to 1 pm2 (organelle) or 1 pm (plasma membrane) and
the means and standard error of means calculated.
RESULTS
We analyzed several developmental stages of ovine
embryos up to blastula stage by means of colloidal gold
conjugated lectins. The results refer to the frequency of
the gold particles on the cell membrane (the free cell
surface and the intercellular membrane were distinguished), some organelles (intracytoplasmic vesicles
and lysosomes), and the zona pellucida.
Cleavage
The results obtained during the cleavage period have
been analyzed as a whole although we carried out a
complete study of 8-cell stage, early morula and compact morula. Throughout these stages neither qualitative nor quantitative differences were found, and thus
the data are summarized a s a whole in Table 2.
On the free cell surface a sparse staining appeared
for LcH, DBA, SBA, MPA, and PNA lectins and a light
staining for WGA lectin. The intercellular contact surface of the ovine embryonic cells during cleavage (Fig.
la,b) showed light quantity of GalNAc (DBA and SBA)
and GlcNAc (WGA)residues but sialic acid was absent.
Intracytoplasmic vesicles (Fig. lc,d) were very heavily
stained with Con A (MadGlc) and WGA (GlcNAc) lectins. In contrast, lysosomes sparsely showed Man/Glc
(Con A) residues.
Concerning the zona pellucida (Fig. 2) we were able
to detect a very heavy reaction with WGA lectin, as
well as a heavy reaction with DBA (GalNAc), SBA
(GalNAc), MPA (Gal), and PNA (Gal) lectins.
Blasfocyst
When the embryo reached the blastocyst stage the
lectin labelling shown by the two cell populations, trophectodermal cells and inner cell mass, was separately
evaluated.
The lectin binding profile of the blastocyst zona pellucida (Fig. 2) is similar to the patterns shown during
cleavage stages: very heavy staining for WGA, light for
MPA and PNA and sparse for DBA and GS-11. Only
SBA and DBA lectins decreased their reactions in this
phase, which means that GalNAc residues were lost.
Trophectoderm
The outer cell surface of the trophectodermal cells
appeared remarkably marked with WGA and LcH lectins (Fig. 3a,c) and lightly stained by SBA (Fig. 3b),
MPA and PNA lectins (Fig. 3d). However, the reaction
shown by DBA, LPA (Fig. 3e), and UEA-I lectins was
sparse. A poor labelling of the intercellular zones was
evidenced except for Con A and UEA-1 lectins. The
reaction to lectins of the free cell surface of the ovine
blastocyst varied qualitatively and quantitatively with
respect to cleavage period. There was a n increase in
staining for LcH, SBA, WGA, MPA, and PNA and new
binding sites for UEA-I and LPA. Concerning the intercellular membrane, there was a specific loss of staining due to the lack of DBA and to the decrease of SBA
and WGA staining.
P. DE PAZ ET AL.
540
Fig. 1. Sections of cleavage-stages sheep embryos. a: DBA lectin. A light staining of intercellular
surfaces is shown ( x 84,000). b: WGA lectin. The intercellular membrane area shows a light labelling
( x 84,000). c: ConA lectin. A specific staining is observed in intracytoplasmic vesicles from the 8 cell
embryo ( X 84,000). d WGA lectin. Intracytoplasmic vesicles with a heavy labelling ( X 84,000).
A heavy reaction to the Con A lectin (Fig. 3f) and a
light one to LcH and WGA lectins was found in the
intracytoplasmic vesicles from ovine blastulae. Lysosomes were also very heavily marked by WGA (Fig.
3g), lightly by Con A (Fig. 3h), and sparsely by LcH.
The specific labelling pattern shown by cell organelles
at the blastula stage was quite different. Intracytoplasmic vesicles globally reduced their staining with WGA
with respect to cleavage stages. In contrast, lysosomes
increased their staining with WGA and LcH lectins.
Inner Cell Mass
There is no specific polarity in the cell membrane of
the blastocyst internal mass. This cell membrane
showed a sparse histochemical reaction against the colloidal gold-conjugated lectins used in this study (Fig.
4a).
The intensity of reaction showed by lysosomes varied
in WGA (very heavy), LcH (light), and Con A (sparse).
Nevertheless the intracytoplasmic vesicles reacted
sparsely with LcH and WGA (Fig. 4b,c) and remarkably with Con A (Fig. 4d). Like the trophectodermal
cells, the intracytoplasmic vesicles and the lysosomes
from ICM blastomeres showed qualitative and quantitative differences with respect to the cleavage period.
DISCUSSION
The results obtained in the present work demonstrate a specific pattern in the distribution of sugar
residues in the preimplantation ovine embryo. During
ovine embryo cleavage the zanes that showed most
sugar residues detected by colloidal gold conjugated
lectins were the zona pellucida (GlcNAc), the intracytoplasmic vesicles (Man/Glc and GlcNAc), and the intercellular contact surface (GlcNAc and GalNAc). In
contrast, a t the blastocyst stage, lectin labelling reduced in the intercellular surfaces but sugar residues
increased on the free cell membrane (ManiGlc,
GlcNAc, and Gal) and lysosomes (GlcNAc).
The zona pellucida presents abundant GalNAc,
GlcNAc, and Gal residues during preimplantation
ovine embryo, but a t the blastocyst stage GalNAc residues are less abundant.
LcH and Con A lectins, with Man/Glc affinity mainly
bound to free cell surface in the trophoblast cells and to
vesicles in the different stages of early ovine develop-
LECTIN RECEPTORS IN EARLY OVINE EMBRYO
54 1
Fig. 2. Zona pellucida. a: WGA lectin. A very heavy labelling is observed ( X 24,000). b: DBA lectin
84,000). c: MPA lectin ( x 84,000). d PNA lectin ( x 84,000).
(x
ment. The changes in the Con A distribution patterns zones. The presence of SBA in the basal membrane of
of the cell surface of the preimplantation embryo have the ectoderm and other epithelial structures has been
already been described in mouse (Wu, 1980; Chavez, reported in the 7-day mouse embryo (Herken et al.,
1990) and rabbit (Chen and Cao, 1992). Handyside 1990). Kimber and Bird (1985) have located DBA re(1980) has experimentally shown a polarization of the ceptors in 8 cell mouse embryos (compaction phase) and
Con A binding sites in isolated blastomeres during mu- suggested a relationship between those receptors and
rine embryo compaction. This author suggests that the compaction phase. In the same way we can relate
such a distribution pattern of Con A receptors could cleavage and the abundant DBA staining observed in
provide a molecular mechanism for attaining spatial the ovine intercellular surface.
differentiation of trophectoderm and inner cell mass
The lectins with high affinity to galactose (MPA and
within the blastocyst. Kimber and Bird (1985) have PNA) show a sparse binding pattern throughout the
shown that the recovery of the cell surface glycoconju- preimplantation period, except in the trophectodermal
gates in the 8-16 cell embryo after enzymatic dissoci- microvilli and zona pellucida. In this sense, Handyside
ation occurs at the same time a s recompaction, so these (1980) has described PNA receptors in murine morulae
glycoconjugates may be involved in this process. This with a sparse staining a t the early stages, which inobservation agrees with the quantitative polarization creased a t the 16 cell stage after compaction. Rober and
in the Man/Glc (LcH and Con A lectins) we found in the Holtz (1988) located galactose and fucose on the emintercellular surface of the trophoblast cells during bryonic membranes during pig embryo implantation
ovine embryo cleavage.
which disappear once the materno-fetal contact is esDBA and SBA staining patterns indicate a sparse tablished. D-galactose residues would play a role in the
density of GalNAc residues in the free cell membrane implantation process as demonstrated by glycosylglycoconjugates of the blastomeres during cleavage, transferase treatments (Chavez, 1990). The exclusive
but in the intercellular contact zones that density is presence of galactose residues at the free membrane
higher. At the blastocyst stages, the free cell surface trophoblastic cells agrees with this hypothetic role.
was richer in GalNAc residues than intercellular
The absence of Lotus staining and the poor density of
Fig. 3
LECTIN RECEPTORS IN EARLY OVINE EMBRYO
543
Fig. 4. Inner cell mass of the sheep blastocyst. a: WGA lectin. Lectin receptors are observed in the
intercellular membrane ( x 84,000). b LcH lectin. Intracytoplasmic vesicles and lysosomes showing gold
colloidal particles ( x 63.000). c: ConA lectin. Secondary lysosome ( x 84,000). d WGA lectin. Lysosome
( x 84,000).
colloidal gold UEA-conjugated particles indicates the
lack of fucosyl residues in the ovine preimplantation
embryo. In contrast, Kimber and Bird (1985) and Dealtry and Sellens (1987) described the presence of receptors to fucose specific lectins in the preimplantation
mouse embryo. Likewise, during preimplantation embryonic development we have only sparsely detected
sialic acid residues (LPA) in the microvilli of the blastocyst trophectodermal cells. Chavez (1990) reported
the presence of sialic acid residues on the trophoblast
in the mouse. According to this author a loss of these
residues is necessary to accomplish implantation.
While GS-I1 receptors were not detected in the ovine
Fig. 3. Trophectoderm of the sheep blastocyst. a: LcH lectin. Detail
of the cell surface microvilli ( x 84,000).b: SBA lectin. Free surface of
the blastomeres shows numerous microvilli i x 84,000).c: WGA lectin.
Gold colloidal particles in the microvilli ( x 84,000). d: MPA lectin.
Sparse staining in cell membrane ( x 84,000).e: LPA lectin. Cell membrane ( x 84,000). f:ConA lectin. Intracytoplasmic vesicles i x 84,000).
g: lectin WGA. Very heavy labelling in a lysosome ( x 63,000). h
ConA lectin. Secondary lysosome ( x 84,000).
embryo during the stages analyzed, WGA shows the
highest staining in our panel of lectin staining, indicating a greater distribution of GlcNAc residues during
these development phases. These wide differences in
the staining with GS-I1 and WGA lectins (both lectins
have the same sugar affinity) may be due to the fact
that GS-I1 lectin has high affinity and interacts with a
non-reducing terminal GlcNAc group, but WGA has
wider binding sites where 2-6 sugar residues can fit
(Goldstein and Poretz, 1986). In contrast to our results,
Kimber and Bird (1985) located BSL-I1 (GS-11) receptors in the preimplantation mouse embryo. Cell membranes from preimplantation ovine embryo show abundant GlcNAc residues, specially in the microvilli of the
trophoblastic cells. Intracytoplasmic vesicles during
cleavage and lysosomes in the zonal blastocyst also
show abundant GlcNAc residues.
The intracytoplasmic vesicles from mammal embryos do not have a definite function. An energy reserve function and a role in the cavitation process
within the blastula have been proposed in other models
(Mohr and Trounson, 1982) for embryos other than
ovine. In the present work, we found a significant cy-
544
P. DE PAZ ET AL.
tochemical identity of vesicles and lysosomes during
preimplantation development which demonstrated
these vesicles could be related to lysosomes in a n intracellular cycle. In this sense, Hyttel et al. (1988) suggest that the intracytoplasmic vesicles from bovine fertilized oocytes are involved in the formation of
metabolic cell complexes. With respect to the participation of these organelles in the cavitation process, the
intracytoplasmic vesicles of morula cell are heavily
stained for ConA (MadGlc) a n WGA (GlcNac) but i t is
sparse in the intercellular of trophectodermal cells.
This could mean that intracytoplasmic vesicles do not
suffer exocytosis during the cavitation process or the
sugar residues of glicoproteins are modified, since no
membranes appear with such a definite staining in the
blastocoele.
The abundant labelling of the ovine zona pellucida
for Gal, GalNac, and GlcNac sugars during the preimplantation period is in agreement with the observations made by several authors (Kan et al., 1990; Shalghi et al., 1991; Miller et al., 1993). In this sense, it is
highly significant that the zona pellucida is a distinctive extracellular matrix to which have been attributed
the functions of species specificity of fertilization, block
to polyspermy, and protection of the embryo during
early development (Riddell et al., 1992). Boice et al.
(1992) indicated that the bovine oviduct-specific secretory glycoconjugates become intimately associated
with early cleavage stage embryos, thus possibly playing a critical role in normal embryonic development.
The differences in sugar composition described in the
ovine preimplantation embryo should reflect molecular characteristics whose developmental variations
may have a functional significance. In the present
work we detect a regional polarization of ManIGlc (Con
A and LcH), GalNAc (DBA and SBA), and GlcNAc
(WGA) residues in the intercellular contact zone of the
blastomeres during cleavage when they are compared
with the cell free surface. In contrast, the increase in
the trophoblast cell membrane of some carbohydrates
previously identified during cleavage (Man/Glc,
GlcNAc, and Gal) is evidence of cell surface modifications, and so they could play a basic role during the
preimplantation period.
ACKNOWLEDGMENTS
This work was supported by the CICYT grant
GAN88-0102.
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involvement of cell surface p-1,4 galactosyltransferase during
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Evans 1981 Stage-specific embryonic antigen involves al-3 fucosylated type 2 blood group chains. Nature, 292t156-158.
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ultrastructure, ovina, lectin, embryo, localization, receptors, preimplantation
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