The lin-12 and glp-1 genes of Caenorhabditis elegans are members of the lin-12/Notch family of receptors for intercellular signals that specify cell fate. By screening for suppressors of a lin-12 gain-of-function mutation, we identified a new gene, sel-12, which appears to function in receiving cells to facilitate signalling mediated by lin-12 and glp-1. The sel-12 gene encodes a protein with multiple transmembrane domains, and is similar to S182, which has been implicated in early-onset familial Alzheimer's disease. The high degree of sequence conservation suggests that the function of the SEL-12 and S182 proteins may also be conserved.
Intermittent viremia occurred frequently and was associated with higher levels of replication (Merck 035), but was not associated with virologic failure in patients receiving initial combination therapy of indinavir-zidovudine-lamivudine (ACTG 343 and Merck 035). In this population, treatment changes may not be necessary to maintain long-term virologic suppression with low-level or intermittent viremia.
We provide evidence that normal human presenilins can substitute for Caenorhabditis elegans SEL-12 protein in functional assays in vivo. In addition, six familial Alzheimer disease-linked mutant human presenilins were tested and found to have reduced ability to rescue the sel-12 mutant phenotype, suggesting that they have lower than normal presenilin activity. A human presenilin 1 deletion variant that fails to be proteolytically processed and a mutant SEL-12 protein that lacks the C terminus display considerable activity in this assay, suggesting that neither presenilin proteolysis nor the C terminus is absolutely required for normal presenilin function. We also show that sel-12 is expressed in most neural and nonneural cell types in all developmental stages. The reduced activity of mutant presenilins and as yet unknown gain-of-function properties may be a contributing factor in the development of Alzheimer disease.
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