Keratin 8 protection of placental barrier function.
Bottom Line: The ConA-induced failure of the trophoblast giant cell barrier results in hematoma formation between the trophoblast giant cell layer and the embryonic yolk sac in a phenocopy of dying K8-deficient concepti in a sensitive genetic background.We conclude the lethality of K8-/- embryos is due to a TNF-sensitive failure of trophoblast giant cell barrier function.The keratin-dependent protection of trophoblast giant cells from a maternal TNF-dependent apoptotic challenge may be a key function of simple epithelial keratins.
Affiliation: The Burnham Institute, La Jolla, CA 92037, USA.
The intermediate filament protein keratin 8 (K8) is critical for the development of most mouse embryos beyond midgestation. We find that 68% of K8-/- embryos, in a sensitive genetic background, are rescued from placental bleeding and subsequent death by cellular complementation with wild-type tetraploid extraembryonic cells. This indicates that the primary defect responsible for K8-/- lethality is trophoblast giant cell layer failure. Furthermore, the genetic absence of maternal but not paternal TNF doubles the number of viable K8-/- embryos. Finally, we show that K8-/- concepti are more sensitive to a TNF-dependent epithelial apoptosis induced by the administration of concanavalin A (ConA) to pregnant mothers. The ConA-induced failure of the trophoblast giant cell barrier results in hematoma formation between the trophoblast giant cell layer and the embryonic yolk sac in a phenocopy of dying K8-deficient concepti in a sensitive genetic background. We conclude the lethality of K8-/- embryos is due to a TNF-sensitive failure of trophoblast giant cell barrier function. The keratin-dependent protection of trophoblast giant cells from a maternal TNF-dependent apoptotic challenge may be a key function of simple epithelial keratins.
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Mentions: We also tested the influence of TNFR2 deficiency on K8−/− viability. K8+/−(FVB/N) mice were bred with TNFR2−/− (B6;129), and progeny were backcrossed with TNFR2−/−(B6;129) to generate K8+/−;TNFR2−/− males and either K8+/−;TNFR2−/− or K8+/−;TNFR2+/− mothers (analogous to C1 and C3 crosses of Fig. 2 A). The absence of TNFR2 in mothers resulted in a more than fourfold increase in the frequency of K8−/− progeny (Fig. 4 A). The difference between the recoveries of K8−/− progeny was statistically significant (Fig. 4 B). However, TNFR2 deficiency also failed to completely rescue K8−/− lethality (Fig. 4 C). TNFR2-deficient embryos were found as frequently as TNFR2 heterozygotes. Thus, both embryonic TNFR2 and TNF are dispensable for embryonic development. In the presence of maternal TNFR2, K8−/− embryos with an absence of TNFR2 were not recovered more frequently than K8−/− embryos with TNFR2 (Fig. 3 A, C3). Thus, the possible modulation of TNFR2 signaling by K8/K18 is not sufficient to ensure embryo survival. The recovery of K8+/+ and K8+/− animals was statistically not distinguishable from the expected number based on Mendelian inheritance (Fig. 3 C). The lower recovery of K8−/− embryos from the C3 cross with TNFR2− compared with the analogous C3 cross with TNF− may be due to differences in the contributions of the B6 and 129 genetic backgrounds in the TNF−/− and TNFR2−/− mouse strains. These results indicate that maternal TNFR2 contributes to the death of K8−/− embryos but provides no support for a role for embryonic TNFR2 in the death of K8−/− embryos.