The susceptibility of xenografts to hyperacute rejection is postulated to reflect in part failure of complement regulatory proteins (CRPs) to control activation of heterologous complement on graft endothelium. To test this concept, transgenic swine expressing the human CRP decay accelerating factor and CD59 were developed using a novel expression system involving transfer of the proteins from erythrocytes to endothelial cells. Hearts from transgenic swine transplanted into baboons had markedly less vascular injury and functioned for prolonged periods compared to hearts from nontransgenic swine. These results indicate that expression of human CRPs in xenogeneic organs may contribute to successful xenografting and suggest that intercellular protein transfer might be a useful approach for expression of heterologous proteins in endothelial cells.

Timely acquisition of cell fates and the elaborate control of growth in numerous organs depend on Notch signaling. Upon ligand binding, the core transcription factor RBP-J activates transcription of Notch target genes. In the absence of signaling, RBP-J switches off target gene expression, assuring the tight spatiotemporal control of the response by a mechanism incompletely understood. Here we show that the histone demethylase KDM5A is an integral, conserved component of Notch/RBP-J gene silencing. Methylation of histone H3 Lys 4 is dynamically erased and re-established at RBP-J sites upon inhibition and reactivation of Notch signaling. KDM5A interacts physically with RBP-J; this interaction is conserved in Drosophila and is crucial for Notch-induced growth and tumorigenesis responses. Supplemental material is available at http://www.genesdev.org.

The evolutionarily conserved Notch signal transduction pathway regulates fundamental cellular processes during embryonic development and in the adult. Ligand binding induces presenilin‐dependent cleavage of the receptor and a subsequent nuclear translocation of the Notch intracellular domain (NICD). In the nucleus, NICD binds to the recombination signal sequence‐binding protein J (RBP‐J)/CBF‐1 transcription factor to induce expression of Notch target genes. Here, we report the identification and functional characterization of RBP‐J interacting and tubulin associated (RITA) (C12ORF52) as a novel RBP‐J/CBF‐1‐interacting protein. RITA is a highly conserved 36 kDa protein that, most interestingly, binds to tubulin in the cytoplasm and shuttles rapidly between cytoplasm and nucleus. This shuttling RITA exports RBP‐J/CBF‐1 from the nucleus. Functionally, we show that RITA can reverse a Notch‐induced loss of primary neurogenesis in Xenopus laevis. Furthermore, RITA is able to downregulate Notch‐mediated transcription. Thus, we propose that RITA acts as a negative modulator of the Notch signalling pathway, controlling the level of nuclear RBP‐J/CBF‐1, where its amounts are limiting.

No abstract