The Caenorhabditis elegans lin-12 gene encodes a transmembrane protein with overall similarity to Drosophila Notch

The lin-12 gene seems to control certain binary decisions during Caenorhabditis elegans development, from genetic and anatomical studies of lin-12 mutants that have either elevated or reduced levels of lin-12 activity. We report here the complete DNA sequence of lin-12: 13.5 kilobases (kb) derived from genomic clones and 4.5 kb from complementary DNA clones. It is of interest that the predicted product is a putative transmembrane protein, given that many of the decisions controlled by lin-12 activity require cell-cell interactions for the correct choice of cell fate. In addition, the predicted lin-12 product may be classified into several regions, based on amino acid sequence similarities to other proteins. These include extensive overall sequence similarity to the Drosophila Notch protein, which also is involved in cell-cell interactions that specify cell fate; a repeated motif found in proteins encoded by the yeast cell-cycle control genes cdc10 (Schizosaccharomyces pombe) and SWI6 (Saccharomyces cerevisiae); and a repeated motif exemplified by epidermal growth factor, found in many mammalian proteins.     

Identity of tumour necrosis factor and the macrophage-secreted factor cachectin

In mammals, several well-defined metabolic changes occur during infection, many of which are attributable to products of the reticuloendothelial system. Among these changes, a hypertriglyceridaemic state is frequently evident, resulting from defective triglyceride clearance, caused by systemic suppression of the enzyme lipoprotein lipase (LPL). We have found previously that macrophages secrete the hormone cachectin, which specifically suppresses LPL activity in cultured adipocytes (3T3-L1 cells). When originally purified from RAW 264.7 (mouse macrophage) cells, cachectin was shown to have a pI of 4.7, a subunit size of relative molecular mass (Mr) 17,000 and to form non-covalent multimers. A receptor for cachectin was identified on non-tumorigenic cultured cells and on normal mouse liver membranes. A new high-yield purification technique has enabled us to determine further details of the structure of mouse cachectin. We now report that a high degree of homology exists between the N-terminal sequence of mouse cachectin and the N-terminal sequence recently determined for human tumour necrosis factor (TNF). Purified cachectin also possesses potent TNF activity in vitro. These findings suggest that the 'cachectin' and 'TNF' activities of murine macrophage conditioned medium are attributable to a single protein, which modulates the metabolic activities of normal as well as neoplastic cells through interaction with specific high-affinity receptors.     

Structural basis of BMP signalling inhibition by the cystine knot protein Noggin

The interplay between bone morphogenetic proteins (BMPs) and their antagonists governs developmental and cellular processes as diverse as establishment of the embryonic dorsal-ventral axis, induction of neural tissue, formation of joints in the skeletal system and neurogenesis in the adult brain. So far, the three-dimensional structures of BMP antagonists and the structural basis for inactivation have remained unknown. Here we report the crystal structure of the antagonist Noggin bound to BMP-7, which shows that Noggin inhibits BMP signalling by blocking the molecular interfaces of the binding epitopes for both type I and type II receptors. The BMP-7-binding affinity of site-specific variants of Noggin is correlated with alterations in bone formation and apoptosis in chick limb development, showing that Noggin functions by sequestering its ligand in an inactive complex. The scaffold of Noggin contains a cystine (the oxidized form of cysteine) knot topology similar to that of BMPs; thus, ligand and antagonist seem to have evolved from a common ancestral gene.     

ICOS is critical for CD40-mediated antibody class switching

The inducible co-stimulatory molecule (ICOS) is a CD28 homologue implicated in regulating T-cell differentiation. Because co-stimulatory signals are critical for regulating T-cell activation, an understanding of co-stimulatory signals may enable the design of rational therapies for immune-mediated diseases. According to the two-signal model for T-cell activation, T cells require an antigen-specific signal and a second, co-stimulatory, signal for optimal T-cell activation. The co-stimulatory signal promotes T-cell proliferation, lymphokine secretion and effector function. The B7-CD28 pathway provides essential signals for T-cell activation, but does not account for all co-stimulation. We have generated mice lacking ICOS (ICOS-/- ) to determine the essential functions of ICOS. Here we report that ICOS-/- mice exhibit profound deficits in immunoglobulin isotype class switching, accompanied by impaired germinal centre formation. Class switching was restored in ICOS-/- mice by CD40 stimulation, showing that ICOS promotes T-cell/B-cell collaboration through the CD40/CD40L pathway.