Chemistry Reference
In-Depth Information
Figure 24.4
Glycan profi ling of mammalian
blastocysts using lectins and confocal laser
scanning microscopy. The upper panel shows
a horse blastocyst prior to hatching. In this
species, the trophoblast cells produce a glyco-
protein capsule replacing the ZP and the blas-
tocyst remains spherical during further growth.
The specimen was stained with WGA and SNA
and in addition with the DNA-binding dye DAPI
to visualize cell nuclei (for information on the
two mentioned plant lectins, please see Chapter
18). (a-c) Optical sections through the center
of the embryo: (a) overlay image of the three
fl uorescent stainings, and (b) WGA and (c)
SNA alone, respectively. The lower panel shows
a hatching bovine blastocyst, which will elon-
gate to a long fi lamentous conceptus. The
specimen was stained with SNA, DAPI (see
above) and fl uorescent phalloidin marking the
F-actin microfi lament cytoskeleton. (d) Central
optical section, (e) and (f) maximum intensity
projections computed from 170 serial optical
sections; (d) and (e) overlay images of the three
fl uorescent stainings, (f) SNA alone. Scale
bars = 100
m.
μ
ences in the morphological structure and in the carbohydrate signature across the
ZP [1]. The differences in lectin-binding patterns between species appear to cor-
relate with their phylogenetic distance. Of particular note in terms of spatial access
to a receptor is that most variations appear to reside in the nonreducing ends of
the ZP glycans. Rather small structural differences at strategic positions can well
be important for establishing species- dependent sperm - ZP interactions. This
concept holds similarly true for infl ammatory or metastatic tumor cells homing
to distinct endothelia (please see Chapters 25 and 27). In terms of methodology,
these studies exemplify the use of plant lectins as versatile laboratory reagents
referred to in Chapter 18.4 .
On the way to identify ZP ligands and sperm receptors, the actual ZP-sperm
interactions in several species were examined by monitoring sperm binding to the
ZP and/or defi ned putative ligands
in vitro.
The results point to different oligosac-
charides of the ZP as key molecules in species- specifi c sperm - ZP interaction. As
an example, in mice a Lewis
x
( Le
x
) - containing glycan (Gal
β
1,4[
α
1,3Fuc]GlcNAc - R)
