Project description:Inosine 5'-phosphate dehydrogenase (impdh) has been well known as a key enzyme in GTP biosynthesis pathway. We found that three isoforms of impdh in zebrafish, namely impdh1a, impdh1b and impdh2, all show robust circadian expression.To examine the molecular functions of three impdh isoforms in zebrafish on the genome scale, we measured the global expression changes of impdh1a, impdh1b and impdh2 morpholino injected larvae (morphants) respectively using RNA-seq. Wild type (WT), control and three impdh morphants were collected at 32 hpf. In our RNA-seq result, we identified 468, 331 and 1166 significant genes affected by impdh1a, impdh1b and impdh2 morpholino (MO) knock-down respectively. Among them, there are limited overlaps between genes affected by different MOs and only 36 genes in common among all three MOs. This indicates that the three impdh isoforms have distinct molecular functions. To knock down the target genes, three impdh MOs and control MO were pressure-injected into 1- to 2-cell stage embryos. WT, control and three impdh morphants were raised at 28°C under 14h: 10h light/dark cycle from birth and sampled simultaneously at 32 hpf. Each group has at least 40 embryos.
Project description:Cell cycle and metabolism are two major outputs controlled by circadian rhythm in many organisms. Here we show that the three processes were linked through inosine 5'-phosphate dehydrogenase (impdh), a rate-limiting enzyme in de novo purine synthesis. We using adult zebrafish as a model system,we applied a genome-wide transcriptome approach that allowed us to investigate circadian gene expression. The whole-genome transcriptome profiles of adult brain in time-series were assayed on Agilent zebrafish microarrays. We used a similar statistical method to identify zebrafish circadian genes (ZCOG) as our previous study in larval zebrafish. Three isoforms of impdh show strong circadian oscillations in different tissues of zebrafish. impdh1a contributes to the ocular development and pigment synthesis, impdh2 promotes and impdh1b delays the development. By limiting the GTP required by DNA synthesis, impdh2 contributes to the daily rhythm of S phase in cell cycle. Multiple enzymes in the de novo purine synthesis pathway show the same circadian oscillations with peaks similar to impdh2. The circadian expression of this pathway is conserved in mouse liver. In summary, we show that the circadian regulation of de novo purine synthesis that supplies crucial building blocks for DNA replication is critical for gating cell cycle in circadian rhythm. Adult zebrafish were sacrificed and dissected at 4h intervals starting at CT0 in both LD and DD conditions for 12 time points. Total RNA of individual zebrafish brain was extracted using Trizol (Invitrogen, Carlsbad, CA) according to the manufacturerM-bM-^@M-^Ys instruction. Microarrays were manufactured by Agilent Technologies (Agilent Technologies, Palo Alto, CA), containing 43,603 probes for zebrafish whole-genome transcriptional profiling.
Project description:Inosine 5'-phosphate dehydrogenase (impdh) has been well known as a key enzyme in GTP biosynthesis pathway. We found that three isoforms of impdh in zebrafish, namely impdh1a, impdh1b and impdh2, all show robust circadian expression.To examine the molecular functions of three impdh isoforms in zebrafish on the genome scale, we measured the global expression changes of impdh1a, impdh1b and impdh2 morpholino injected larvae (morphants) respectively using RNA-seq. Wild type (WT), control and three impdh morphants were collected at 32 hpf. In our RNA-seq result, we identified 468, 331 and 1166 significant genes affected by impdh1a, impdh1b and impdh2 morpholino (MO) knock-down respectively. Among them, there are limited overlaps between genes affected by different MOs and only 36 genes in common among all three MOs. This indicates that the three impdh isoforms have distinct molecular functions.
Project description:Cell cycle and metabolism are two major outputs controlled by circadian rhythm in many organisms. Here we show that the three processes were linked through inosine 5'-phosphate dehydrogenase (impdh), a rate-limiting enzyme in de novo purine synthesis. We using adult zebrafish as a model system,we applied a genome-wide transcriptome approach that allowed us to investigate circadian gene expression. The whole-genome transcriptome profiles of adult brain in time-series were assayed on Agilent zebrafish microarrays. We used a similar statistical method to identify zebrafish circadian genes (ZCOG) as our previous study in larval zebrafish. Three isoforms of impdh show strong circadian oscillations in different tissues of zebrafish. impdh1a contributes to the ocular development and pigment synthesis, impdh2 promotes and impdh1b delays the development. By limiting the GTP required by DNA synthesis, impdh2 contributes to the daily rhythm of S phase in cell cycle. Multiple enzymes in the de novo purine synthesis pathway show the same circadian oscillations with peaks similar to impdh2. The circadian expression of this pathway is conserved in mouse liver. In summary, we show that the circadian regulation of de novo purine synthesis that supplies crucial building blocks for DNA replication is critical for gating cell cycle in circadian rhythm.
Project description:Metabolism is the major output of the circadian clock in many organisms. We developed a computational method to integrate both circadian gene expression and metabolic network. Applying this method to zebrafish circadian transcriptome, we have identified large clusters of metabolic genes containing mostly genes in purine and pyrimidine metabolism in the metabolic network showing similar circadian phases. Our metabolomics analysis found that the level of inosine 5'-monophosphate (IMP), an intermediate metabolite in de novo purine synthesis, showed significant circadian oscillation in larval zebrafish. We focused on IMP dehydrogenase (impdh), a rate-limiting enzyme in de novo purine synthesis, with three circadian oscillating gene homologs: impdh1a, impdh1b and impdh2. Functional analysis revealed that impdh2 contributes to the daily rhythm of S phase in the cell cycle while impdh1a contributes to ocular development and pigment synthesis. The three zebrafish homologs of impdh are likely regulated by different circadian transcription factors. We propose that the circadian regulation of de novo purine synthesis that supplies crucial building blocks for DNA replication is an important mechanism conferring circadian rhythmicity on the cell cycle. Our method is widely applicable to study the impact of circadian transcriptome on metabolism in complex organisms.
Project description:The RAS-ERK/MAPK (RAS-extracellular signal-regulated kinase/mitogen-activated protein kinase) pathway integrates growth-promoting signals to stimulate cell growth and proliferation, at least in part, through alterations in metabolic gene expression. However, examples of direct and rapid regulation of the metabolic pathways by the RAS-ERK pathway remain elusive. We find that physiological and oncogenic ERK signaling activation leads to acute metabolic flux stimulation through the de novo purine synthesis pathway, thereby increasing building block availability for RNA and DNA synthesis, which is required for cell growth and proliferation. We demonstrate that ERK2, but not ERK1, phosphorylates the purine synthesis enzyme PFAS (phosphoribosylformylglycinamidine synthase) at T619 in cells to stimulate de novo purine synthesis. The expression of nonphosphorylatable PFAS (T619A) decreases purine synthesis, RAS-dependent cancer cell-colony formation, and tumor growth. Thus, ERK2-mediated PFAS phosphorylation facilitates the increase in nucleic acid synthesis required for anabolic cell growth and proliferation.
Project description:A general method for isotopic labeling of the purine base moiety of nucleotides and RNA has been developed through biochemical pathway engineering in vitro. A synthetic scheme was designed and implemented utilizing recombinant enzymes from the pentose phosphate and de novo purine synthesis pathways, with regeneration of folate, aspartate, glutamine, ATP, and NADPH cofactors, in a single-pot reaction. Syntheses proceeded quickly and efficiently in comparison to chemical methods with isolated yields up to 66% for 13C-, 15N-enriched ATP and GTP. The scheme is robust and flexible, requiring only serine, NH4+, glucose, and CO2 as stoichiometric precursors in labeled form. Using this approach, U-13C- GTP, U-13C, 15N- GTP, 13C 2,8- ATP, and U-15N- GTP were synthesized on a millimole scale, and the utility of the isotope labeling is illustrated in NMR spectra of HIV-2 transactivation region RNA containing 13C 2,8-adenosine and 15N 1,3,7,9,2-guanosine. Pathway engineering in vitro permits complex synthetic cascades to be effected, expanding the applicability of enzymatic synthesis.
Project description:The focus of this review is the human de novo purine biosynthetic pathway. The pathway enzymes are enumerated, as well as the reactions they catalyze and their physical properties. Early literature evidence suggested that they might assemble into a multi-enzyme complex called a metabolon. The finding that fluorescently-tagged chimeras of the pathway enzymes form discrete puncta, now called purinosomes, is further elaborated in this review to include: a discussion of their assembly; the role of ancillary proteins; their locus at the microtubule/mitochondria interface; the elucidation that at endogenous levels, purinosomes function to channel intermediates from phosphoribosyl pyrophosphate to AMP and GMP; and the evidence for the purinosomes to exist as a protein condensate. The review concludes with a consideration of probable signaling pathways that might promote the assembly and disassembly of the purinosome, in particular the identification of candidate kinases given the extensive phosphorylation of the enzymes. These collective findings substantiate our current view of the de novo purine biosynthetic metabolon whose properties will be representative of how other metabolic pathways might be organized for their function.