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J. Cell Biol.,
Volume 139, Number 3, November 3, 1997 735-747
Institut de Génétique et de Biologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique/Institut National de
la Santé et de la Recherche Médicale/Université Louis Pasteur, Collège de France, 67404 Illkirch-Cedex, France
We have generated F9 murine embryonal
carcinoma cells in which either the retinoid X receptor
(RXR)
and retinoic acid receptor (RAR)
genes or
the RXR
and RAR
genes are knocked out, and compared their phenotypes with those of wild-type (WT),
RXR
/
, RAR
/
, and RAR
/
cells. RXR
/
/
RAR
/
cells were resistant to retinoic acid treatment
for the induction of primitive and parietal endodermal
differentiation, as well as for antiproliferative and apoptotic responses, whereas they could differentiate into
visceral endodermlike cells, as previously observed for
RXR
/
cells. In contrast, RXR
/
/RAR
/
cells
were defective for all three types of differentiation, as
well as antiproliferative and apoptotic responses, indicating that RXR
and RAR
represent an essential receptor pair for these responses. Taken together with results obtained by treatment of WT and mutant F9 cells
with RAR isotype- and panRXR-selective retinoids,
our observations support the conclusion that RXR/
RAR heterodimers are the functional units mediating
the retinoid signal in vivo. Our results also indicate that
the various heterodimers can exert both specific and redundant functions in differentiation, proliferation, and
apoptosis. We also show that the functional redundancy
exhibited between RXR isotypes and between RAR
isotypes in cellular processes can be artifactually generated by gene knockouts. The present approach for multiple gene targeting should allow inactivation of any set
of genes in a given cell.
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