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.
Related in: MedlinePlus
Mentions: (FVB/N; B6;129) K8+/−; TNF+/− females were mated with (FVB/N; B6;129) K8−/−; TNF−/− males (both from the experiment shown in Fig. 2) to generate K8+/− and K8−/− embryos within a TNF+/− maternal environment. At E9.5, mothers were treated with ConA, and a portion of each embryo was dissected for PCR analysis, and the remaining concepti were fixed, bisected, and processed for paraffin sections. Embryos removed from the yolk sacs were all similar size and without obvious defects. Stained sections revealed hematoma formation in K8−/− extraembryonic tissues very similar to the phenotype of the spontaneous K8−/− concepti in the B6;129 genetic background at E10.5 (Fig. 5, A–F, and Fig. 1). Hematomas were commonly found between the trophoblast giant cell layer and the parietal yolk sac. Quantitation of bleeding in extraembryonic tissues revealed significantly increased bleeding in K8−/− extraembryonic tissues (Fig. 5, G–I). The average hematoma area for 16 concepti from three litters was 4,578 arbitrary units compared with 1,607 for 14 K8+/− concepti. (P = 0.007, two tailed t test). No significant correlation was found between the degree of bleeding and the TNF genotype of the embryos. Thus, K8−/−concepti are more sensitive to a ConA-induced, maternal TNF-dependent loss of trophoblast giant cells barrier function. This phenotype is similar to that observed for K8−/− concepti in a B6;129 genetic background without ConA treatment. ConA treatment of a single pregnant TNF−/−; K8+/− mother of the same mixed genetic background did not result in visible hematoma formation. This suggests that both liver apoptosis and concepti hematoma formation caused by ConA treatment of pregnant mothers is dependent on maternal TNF.