Flavonoids are representative plant secondary products. In the model plant Arabidopsis thaliana, at least 54 flavonoid molecules (35 flavonols, 11 anthocyanins and 8 proanthocyanidins) are found. Scaffold structures of flavonoids in Arabidopsis are relatively simple. These include kaempferol, quercetin and isorhamnetin for flavonols, cyanidin for anthocyanins and epicatechin for proanthocyanidins. The chemical diversity of flavonoids increases enormously by tailoring reactions which modify these scaffolds, including glycosylation, methylation and acylation. Genes responsible for the formation of flavonoid aglycone structures and their subsequent modification reactions have been extensively characterized by functional genomic efforts - mostly the integration of transcriptomics and metabolic profiling followed by reverse genetic experimentation. This review describes the state-of-art of flavonoid biosynthetic pathway in Arabidopsis regarding both structural and genetic diversity, focusing on the genes encoding enzymes for the biosynthetic reactions and vacuole translocation.

No abstract

Poly(ADP-ribose)-1 (PARP-1) is a key mediator of cell death in excitotoxicity, ischemia, and oxidative stress. PARP-1 activation leads to cytosolic NAD ϩ depletion and mitochondrial release of apoptosis-inducing factor (AIF), but the causal relationships between these two events have been difficult to resolve. Here, we examined this issue by using extracellular NAD ϩ to restore neuronal NAD ϩ levels after PARP-1 activation. Exogenous NAD ϩ was found to enter neurons through P2X 7 -gated channels. Restoration of cytosolic NAD ϩ by this means prevented the glycolytic inhibition, mitochondrial failure, AIF translocation, and neuron death that otherwise results from extensive PARP-1 activation. Bypassing the glycolytic inhibition with the metabolic substrates pyruvate, acetoacetate, or hydroxybutyrate also prevented mitochondrial failure and neuron death. Conversely, depletion of cytosolic NAD ϩ with NAD ϩ glycohydrolase produced a block in glycolysis inhibition, mitochondrial depolarization, AIF translocation, and neuron death, independent of PARP-1 activation. These results establish NAD ϩ depletion as a causal event in PARP-1-mediated cell death and place NAD ϩ depletion and glycolytic failure upstream of mitochondrial AIF release.

Two 21-hydroxylase [P450(C21)] genes have been isolated from a human genomic library using a bovine P-450(C21) cDNA. The insert DNAs containing the P450(C21) genes were also hybridized with the sequences of the 5' or 3' end regions of human C4 cDNA, indicating a close linkage of the P450(C21) gene to the C4 gene. Sequence analysis has revealed that the two P450(C21) genes are both 3.4 kilobases long and split into 10 exons. Comparing the two sequences, we found that the two genes are highly homologous including their introns and flanking sequences, but that three mutations render one of the two P450(C21) genes nonfunctional-i base insertion, an 8-base deletion, and a transition mutation-all of which may cause premature termination of the translation.

Overexpression of zinc finger E-box binding homeobox transcription factor 1 (Zeb1) in cancer leads to epithelial-to-mesenchymal transition (EMT) and increased metastasis. As opposed to overexpression, we show that mutation of Zeb1 in mice causes a mesenchymal-epithelial transition in gene expression characterized by ectopic expression of epithelial genes such as E-cadherin and loss of expression of mesenchymal genes such as vimentin. In contrast to rapid proliferation in cancer cells where Zeb1 is overexpressed, this mesenchymal-epithelial transition in mutant mice is associated with diminished proliferation of progenitor cells at sites of developmental defects, including the forming palate, skeleton and CNS. Zeb1 dosage-dependent deregulation of epithelial and mesenchymal genes extends to mouse embryonic fibroblasts (MEFs), and mutant MEFs also display diminished replicative capacity in culture, leading to premature senescence. Replicative senescence in MEFs is classically triggered by products of the Ink4a (Cdkn2a) gene. However, this Ink4a pathway is not activated during senescence of Zeb1 mutant MEFs. Instead, there is ectopic expression of two other cell cycle inhibitory cyclin-dependent kinase inhibitors, p15Ink4b (Cdkn2b) and p21Cdkn1a (Cdkn1a). We demonstrate that this ectopic expression of p15Ink4b extends in vivo to sites of diminished progenitor cell proliferation and developmental defects in Zeb1-null mice.