Timing and mechanism of conceptus demise in a complement regulatory membrane protein deficient mouse

Problem

Crry is a widely expressed type 1 transmembrane complement regulatory protein in rodents which protects self‐tissue by downregulating C3 activation. Crry^?/? concepti produced by Crry^+/? × Crry^+/? matings are attacked by maternal complement system leading to loss before day 10. The membrane attack complex is not the mediator of this death. We hypothesized that the ability of C3b to engage the alternative pathway's feedback loop relatively unchecked on placental membranes induces the lesion yielding the demise of the Crry^?/? mouse.

Method of Study

We investigated the basis of Crry^?/? conceptus demise by depleting maternal complement with cobra venom factor and blocking antibodies. We monitored their effects primarily by genotyping and histologic analyses.

Results

We narrowed the critical period of the complement effect from 6.5 to 8.5 days post‐coitus (dpc), which is immediately after the conceptus is exposed to maternal blood. Deposition by 5.5 dpc of maternal C3b on the placental vasculature lacking Crry^?/? yielded loss of the conceptus by 8.5 dpc. Fusion of the allantois to the chorion during placental assembly did not occur, fetal vessels originating in the allantois did not infiltrate the chorioallantoic placenta, the chorionic plate failed to develop, and the labyrinthine component of the placenta did not mature.

Conclusion

Our data are most consistent with the deposition of C3b being responsible for the failure of the allantois to fuse to the chorion leading to subsequent conceptus demise.

     

Man1, an inner nuclear membrane protein,regulates left–right axis formation by controlling nodal signaling in a node‐independent manner

Man1, an inner nuclear membrane protein, regulates transforming growth factor β signaling by interacting with receptor‐associated Smads. In Man1‐deficient (Man1^Δ/Δ) embryos, vascular remodeling is perturbed by misregulation of Smad activity. Here, we show that Man1^Δ/Δ embryos exhibit abnormal heart morphogenesis including the looping abnormality. We searched for the molecular basis underlying the heart abnormalities and found that the left side‐specific genes responsible for left–right (LR) asymmetry, Nodal, Lefty2, and Pitx2, were expressed bilaterally in the lateral plate mesoderm and that their expression was enhanced significantly in mutants. Notably, Lefty1, a marker for the midline barrier, was maintained in Man1^Δ/Δ mutants. Crossing Man1^Δ/+ with Nodal hypomorphs (Nodal^neo/+), in which Nodal signaling in the node is disrupted, to generate double homozygous embryos (Man1^Δ/Δ; Nodal^neo/neo) revealed that the bilateral Nodal was retained in Man1^Δ/Δ; Nodal^neo/neo embryos. These results suggest that Man1 regulates LR asymmetry by controlling Nodal signaling in a node‐independent manner. Developmental Dynamics 237:3565–3576, 2008. © 2008 Wiley‐Liss, Inc.     

Cell lines that support replication of a novel herpes simplex virus 1 UL31 deletion mutant can properly target UL34 protein to the nuclear rim in the absence of UL31

Previous results indicated that the herpes simplex virus 1 (HSV-1) U(L)31 gene is necessary and sufficient for localization of the U(L)34 protein exclusively to the nuclear membrane of infected Hep2 cells. In the current studies, a bacterial artificial chromosome containing the entire HSV-1 strain F genome was used to construct a recombinant viral genome in which a gene encoding kanamycin resistance was inserted in place of 262 codons of the 306 codon U(L)31 open reading frame. The deletion virus produced virus titers approximately 10- to 50-fold lower in rabbit skin cells, more than 2000-fold lower in Vero cells, and more than 1500-fold lower in CV1 cells, compared to a virus bearing a restored U(L)31 gene. The replication of the U(L)31 deletion virus was restored on U(L)31-complementing cell lines derived either from rabbit skin cells or CV1 cells. Confocal microscopy indicated that the majority of U(L)34 protein localized aberrantly in the cytoplasm and nucleoplasm of Vero cells and CV1 cells, whereas U(L)34 protein localized at the nuclear membrane in rabbit skin cells, and U(L)31 complementing CV1 cells infected with the U(L)31 deletion virus. We conclude that rabbit skin cells encode a function that allows proper localization of U(L)34 protein to the nuclear membrane. We speculate that this function partially complements that of U(L)31 and may explain why U(L)31 is less critical for replication in rabbit skin cells as opposed to Vero and CV1 cells.     

Viral regulators of complement activation: Structure,function and evolution

The complement system surveillance in the host is effective in controlling viral propagation. Consequently, to subvert this effector mechanism, viruses have developed a series of adaptations. One among these is encoding mimics of host regulators of complement activation (RCA) which help viruses to avoid being labeled as ‘foreign’ and protect them from complement-mediated neutralization and complement-enhanced antiviral adaptive immunity. In this review, we provide an overview on the structure, function and evolution of viral RCA proteins.