The mammalian CoREST ([co]repressor for element-1-silencing transcription factor) complex was first identified associated with the repressor for element-1 silencing transcription factor (REST)/neuronal restrictive silencing factor. The CoREST complex is a chromatin-modifying corepressor complex that acts with REST to regulate neuronal gene expression and neuronal stem cell fate. Components of a CoREST-like complex have been identified recently in Xenopus laevis, Caenorhabditis elegans, and Drosophila melanogaster. Like the mammalian complex, the Drosophila complex is required to regulate neuronal gene expression, whereas the C. elegans homologs regulate the expression of the hop-1 presenilin gene, suggesting an ancient conserved function of CoREST complexes in regulating neuronal gene expression.
Previous work has shown that reduction-of-function mutations in the genes daf-2 and age-1 can increase adult life (Age phenotype) of Caenorhabditis elegans and that certain daf-12 alleles considerably amplify this effect in daf-2; daf-12 doubles. We have measured the light production potential (LPP) and alkaline phosphatase (ALP) and protein tyrosine kinase (PTK) activity levels as suitable biochemical markers to further investigate genetic interactions between these genes. The light production assay measures superoxide anion production by freeze-thawed worms in assay medium containing sufficient amounts of nicotineamide adenine dinucleotide, reduced form (NADH) and nicotineamide adenine dinucleotide phosphate, reduced form (NADPH) to drive the chemiluminescent reaction at maximal speed, and 5 mM cyanide to fully repress cytosolic superoxide dismutase (SOD). This assay thus provides an estimate of the maximum output of the metabolic pathways involved at the instant of freeze-fixation, and under the condition of the assay. LPP and PTK activities decreased similarly in daf-12(m20), and a control strain that had wild-type alleles of daf-12, age-1, and daf-2. The age-dependent decrease of LPP and PTK was reduced in age-1(hx542) and age-1(hx542); daf-2(e1370), and virtually absent in daf-2(e1370) and daf-2(e1370); daf-12(m20) mutant worms. ALP activity increased with age in non-Age genotypes and showed little, if any, age-dependent alteration in daf-2(e1370) and daf-2(e1370); daf-12(m20) mutant worms. Mutation in both age-1 and daf-2 caused no stronger phenotype than a single mutation as estimated by LPP, PTK, and ALP. We propose that (a) daf-2 is the major effector of metabolic activity during adult life, (b) daf-2 downregulates metabolic activity with increasing age, and (c) daf-12 stimulates oxygen consumption independently of daf-2.
Background: Presenilin proteins are part of a complex of proteins that can cleave many type I transmembrane proteins, including Notch Receptors and the Amyloid Precursor Protein, in the middle of the transmembrane domain. Dominant mutations in the human presenilin genes PS1 and PS2 lead to Familial Alzheimer's disease. Mutations in the Caenorhabditis elegans sel-12 presenilin gene cause a highly penetrant egg-laying defect due to reduction of signalling through the lin-12/ Notch receptor. Mutations in six spr genes (for suppressor of presenilin) are known to strongly suppress sel-12. Mutations in most strong spr genes suppress sel-12 by de-repressing the transcription of the largely functionally equivalent hop-1 presenilin gene. However, how mutations in the spr-2 gene suppress sel-12 is unknown.
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