Adhesive interactions mediated by integrins of the beta1 subfamily are thought to be critical in controlling differentiation and migration of blood cell precursors. Here we report that chimaeric mice generated with beta1-integrin-deficient embryonic stem (ES) cells lack beta1(-/-) cells in blood and in haematopoietic organs such as spleen, thymus and bone marrow. Chimaeric embryos contain beta1-null haematopoietic cells in the yolk sac and in fetal blood but not in fetal liver. We show that such beta1(-/-) haematopoietic stem cells derived from yolk sac of 10.5-day-old chimaeric embryos readily generate erythroid and myeloid colonies and that beta1(-/-) ES cells can differentiate into mature B lymphocytes in vitro. Our results indicate that haematopoietic stem cells lacking beta1 integrins can form and differentiate into different lineages but cannot colonize the fetal liver.
Previous reports strongly suggest that, in addition to the nicotinic acetylcholine receptor, rabies virus can use other, as-yet-unidentified receptors. We found that laboratory cell lines susceptible to rabies virus infection express the neural cell adhesion molecule (NCAM) (CD56) on their surface, whereas resistant cells do not, supporting the idea that NCAM could be a rabies virus receptor. We observed that (i) incubation with rabies virus decreases the surface expression of NCAM; (ii) treatment of susceptible cells with heparan sulfate, a ligand for NCAM, or with NCAM antibodies significantly reduces the rabies virus infection; and (iii) preincubation of rabies virus inoculum with soluble NCAM protein as a receptor decoy drastically neutralizes the capacity of rabies virus to infect susceptible cells. Moreover, we demonstrated that transfection of resistant L fibroblasts with the NCAM-encoding gene induces rabies virus susceptibility whereas absence of NCAM in the primary cortical cell cultures prepared from NCAM-deficient mice reduces the rabies virus infection and virus production. This provides evidence that NCAM is an in vitro receptor for the rabies virus. Moreover, the in vivo relevance for the use of NCAM as a receptor was demonstrated by the infection of NCAM-deficient mice, in which rabies mortality was delayed and brain invasion by rabies virus was drastically restricted. Our results showed that NCAM, which is expressed mainly in the adult nervous system, plays an important role in rabies infection. However, it cannot be excluded that receptors other than NCAM are utilized. Thus, the description of NCAM as a new rabies virus receptor would be another example of the use by viruses of more than one receptor to gain entry into the host.
We have isolated the novel gene SMOC-2, which encodes a secreted modular protein containing an EF-hand calcium-binding domain homologous to that in BM-40. It further consists of two thyroglobulin-like domains, a follistatin-like domain and a novel domain found only in the homologous SMOC-1. Phylogenetic analysis of the calcium-binding domain sequences showed that SMOC-1 and -2 form a separate group within the BM-40 family. The human and mouse SMOC-2 sequences are coded for by genes consisting of 13 exons located on chromosomes 6 and 17, respectively. Analysis of recombinantly expressed protein showed that SMOC-2 is a glycoprotein with a calcium-dependent conformation. Results from Northern blots and reverse transcription PCR revealed a widespread expression in many tissues.
We have isolated the novel gene SMOC-1 that encodes a secreted modular protein containing an EF-hand calcium-binding domain homologous to that in BM-40. It further consists of two thyroglobulin-like domains, a follistatin-like domain and a novel domain. Recombinant expression in human cells showed that SMOC-1 is a glycoprotein with a calcium-dependent conformation. Results from Northern blots, reverse transcriptase-PCR, and immunoblots revealed a widespread expression in many tissues. Immunofluorescence studies with an antiserum directed against recombinant human SMOC-1 demonstrated a basement membrane localization of the protein and additionally its presence in other extracellular matrices. Immunogold electron microscopy confirmed the localization of SMOC-1 within basement membranes in kidney and skeletal muscle as well as its expression in the zona pellucida surrounding the oocyte.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.