Mg. Rambotti et al., IMMUNOCYTOCHEMICAL LOCALIZATION OF ANNEXINS-V AND ANNEXINS-VI IN HUMAN PLACENTAE OF DIFFERENT GESTATIONAL AGES, Cellular & molecular biology research, 39(6), 1993, pp. 579-588
The cellular and subcellular localization of annexins V and VI, two me
mbers of a superfamily of Ca2+-dependent phospholipid- and membrane-bi
nding proteins, was investigated in chorionic villi of human placentae
of different gestational ages by postembedding immunocytochemistry at
the electron microscope level. All cell types of placental villi, i.e
., the syncytiotrophoblast, Langhans cells, Hofbauer cells, fibroblast
s, and capillary endothelial cells, appeared to express the two protei
ns, irrespective of the gestational age. By immunogold particle counts
, annexin V was observed to be 2-3 times as much abundant as annexin V
I. Syncytiotrophoblast cells appeared to contain the largest amounts a
nd Langhans cells appeared to contain the least amounts of annexins V
and VI, as judged by immunocytochemistry. The two proteins were found
associated with plasma, Golgi, and vacuolar membranes, and with membra
nes of the endoplasmic reticulum, as well as diffusely in the cytoplas
m. Annexin V appeared to be distributed in nearly equal proportions be
tween cell membranes and the cytoplasm in stromal cells and to be abou
t 30% associated with cell membranes in trophoblast cells, whereas ann
exin VI appeared almost equally distributed between cell membranes and
the cytoplasm in trophoblast and stromal cells. Also, annexins V and
VI appeared to be more abundant in trophoblast cells than in stromal c
ells. The present data strongly support the idea that placenta is a pr
eferential site of annexin-regulated activities, and suggest that anne
xins V and VI are actively involved in the Ca2+-dependent regulation o
f membrane processes in trophoblast cells.