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J. Cell Biol.,
Volume 140, Number 6, March 23, 1998 1453-1461

* Institut für Genetik, Abt. Molekulargenetik, Universität Bonn, 53117 Bonn; and Mice that harbor a targeted homozygous defect in the gene coding for the gap junctional protein
connexin26 died in utero during the transient phase
from early to midgestation. From day 10 post coitum
onwards, development of homozygous embryos was retarded, which led to death around day 11 post coitum.
Except for growth retardation, no gross morphological
alterations were detected between homozygous
connexin26-defective embryos and wild-type littermates.
At day 9 postcoitum, when chorioallantoic placenta
started to function, connexin26 was weakly expressed
in the yolk sac epithelium, between syncytiotrophoblasts I and II in the labyrinth region of the placenta,
and in the skin of the embryo. At day 10 post coitum,
expression of connexin26 in the placenta was much
stronger than at the other locations. To analyze involvement of connexin26 in the placental transfer of
nutrients, we have measured embryonic uptake of the
nonmetabolizable glucose analogue 3-O-[14C]methylglucose, injected into the maternal tail vein. At day 10 post coitum, viable, homozygous connexin26-defective
embryos accumulated only ~40% of the radioactivity
measured in wild-type and heterozygous littermates of
the same size. We conclude that the uptake of glucose,
and presumably other nutrients as well, from maternal
blood into connexin26-deficient mouse embryos was severely impaired and apparently not sufficient to support the rapid organogenesis during midgestation. Our
results suggest that connexin26 gap junction channels
likely fulfill an essential role in the transfer of maternal
nutrients and embryonic waste products between syncytiotrophoblast I and II in the labyrinth layer of the
mouse placenta.
Institut für Anatomie, Universität Essen,
45122 Essen, Germany
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