Tumor necrosis factor receptor (TNFR)-associated factors (TRAFs) are key adaptor molecules in the TNFR-signaling complexes that promote a wide variety of signaling cascades including cell proliferation, activation, differentiation, and apoptosis. TRAF-interacting protein (TRIP) is required for the inhibitory regulation of TNF-induced NF-kappa B signaling via the TNFR/TRAF-signaling complexes in vitro. TRIP also directly interacts with the familial cylindromatosis tumor suppressor gene (CYLD) and negatively regulates NF-kappa B activation in vitro. However, although there appears to be a relationship between TRIP, the TRAFs and also CYLD as modulators of NF-kappa B signaling in vitro, the functional role of TRIP in vivo is still unclear. To identify the role of TRIP in vivo, we have generated TRIP-deficient mice. Homozygous mouse embryos were found to die shortly after implantation due to proliferation defects and excessive cell death. These results indicate that TRIP is an essential factor during early mouse embryonic development in vivo. (C) 2007 Elsevier Inc. All rights reserved.