RAT YOLK-SAC EXPLANTS AS A SYSTEM FOR STUDYING THE REGULATION OF ENDODERMAL GENES - DOWN-REGULATION OF THE ALPHA-FETOPROTEIN GENE BY DEXAMETHASONE AND PHORBOL ESTER
K. Cailliau et al., RAT YOLK-SAC EXPLANTS AS A SYSTEM FOR STUDYING THE REGULATION OF ENDODERMAL GENES - DOWN-REGULATION OF THE ALPHA-FETOPROTEIN GENE BY DEXAMETHASONE AND PHORBOL ESTER, European journal of cell biology, 75(4), 1998, pp. 375-382
The visceral yolk sac is a fetal membrane with essential placental fun
ctions. It is the major site of synthesis of alpha-fetoprotein (AFP),
the most abundant plasma protein in the fetus. We developed a system o
f rat yolk sec explants in serum-free culture medium to study the regu
lation of endodermal gene expression in yolk sac, The explanted yolk s
ac tissues retained their double-sided morphology for up to 48 hours.
The epithelial cells of both layers remained tightly joined on a basem
ent membrane as seen by light and electron microscopy. This probably a
ccounts for the continued expression of several endodermal cell-specif
ic markers, The levels of mRNA encoding AFP, vitamin D-binding protein
(DBP), hepatocyte nuclear factor 1 alpha and beta transcription facto
rs did not change during the 48-hour culture period. This reflects the
stability of the differentiation state of the yolk sac endodermal cel
ls. Dexamethasone and phorbol ester (TPA) specifically reduced the AFP
mRNA level without affecting that of DBP, This suggests that these tr
ansduction pathways are functional in the yolk sac during this period
of gestation and could be involved in the physiological down-regulatio
n of AFP gene expression before birth, AII these results show that thi
s serum-free culture of rat yolk sac explants is a valuable system for
further investigating the action of natural compounds and pharmacolog
ical drugs on endodermal gene expression during the embryonic and feta
l periods.