The Role Of The Glucocorticoids And Insulin In The Regulation Of Hepatic Glucose-6-Phosphate Dehydrogenase

The objective of my research project was to examine how insulin and the glucocorticoids, alone, and in combination, regulate hepatic glucose-6-phosphate dehydrogenase (G6PD) at the level of functional mRNA coding for G6PD. The model system I utilized for these studies was primary cultures of adult rat liver parenchymal cells. These cells were maintained in a serum-free and chemically defined medium so that direct effects of added hormones on the hepatocytes could be ascertained. Dexamethasone (Dex), a synthetic glucocorticoid, when added alone did not have an effect on G6PD activity. Insulin caused about a 1.6-fold increase in enzyme activity, and when Dex and insulin were present together, Dex acted in a permissive manner to amplify the insulin stimulation of G6PD (2.5-fold increase). These effects on enzyme activity were paralleled by increases in the relative rate of G6PD synthesis. Upon measurement of the levels of functional mRNA coding for G6PD it was observed that Dex by itself stimulated G6PD mRNA levels 4-fold while insulin treatment resulted in a 2-fold increase. When Dex and insulin were added together G6PD mRNA levels were increased in an additive fashion (an approximate 7-fold stimulation). The results of my studies suggest that glucocorticoid exerts its regulation on G6PD at the pretranslational level by modulating levels of mRNA coding for G6PD, however, this mRNA is not expressed unless insulin has also been added. Thus insulin would appear to regulate G6PD at the pretranslational level (as evidenced by insulin treatment alone) and possibly at the translational or posttranscriptional level (as evidenced by combined Dex and insulin treatment). More definitive conclusions as to the exact nature of the pretranslational regulation being exerted by Dex and insulin, i.e., whether this represents authentic regulation of gene transcription as opposed to regulation of posttranscriptional events such as mRNA processing, transport of mRNA to the cytoplasm, or stabilization of cytoplasmic mRNA must await the availability of a cDNA probe specific for rat liver glucose-6-phosphate dehydrogenase

The RNA-binding protein, ZFP36L2, influences ovulation and oocyte maturation

ZFP36L2 protein destabilizes AU-rich element-containing transcripts and has been implicated in female fertility. In the C57BL/6NTac mouse, a mutation in Zfp36l2 that results in the decreased expression of a form of ZFP36L2 in which the 29 N-terminal amino acid residues have been deleted, ΔN-ZFP36L2, leads to fertilized eggs that arrest at the two-cell stage. Interestingly, homozygous ΔN-Zfp36l2 females in the C57BL/6NTac strain release 40% fewer eggs than the WT littermates (Ramos et al., 2004), suggesting an additional defect in ovulation and/or oocyte maturation. Curiously, the same ΔN-Zfp36l2 mutation into the SV129 strain resulted in anovulation, prompting us to investigate a potential problem in ovulation and oocyte maturation. Remarkably, only 20% of ΔN-Zfp36l2 oocytes in the 129S6/SvEvTac strain matured ex vivo, suggesting a defect on the oocyte meiotic maturation process. Treatment of ΔN-Zfp36l2 oocytes with a PKA inhibitor partially rescued the meiotic arrested oocytes. Furthermore, cAMP levels were increased in ΔN-Zfp36l2 oocytes, linking the cAMP/PKA pathway and ΔN-Zfp36l2 with meiotic arrest. Since ovulation and oocyte maturation are both triggered by LHR signaling, the downstream pathway was investigated. Adenylyl cyclase activity was increased in ΔN-Zfp36l2 ovaries only upon LH stimulation. Moreover, we discovered that ZFP36L2 interacts with the 3′UTR of LHR mRNA and that decreased expression levels of Zfp36l2 correlates with higher levels of LHR mRNA in synchronized ovaries. Furthermore, overexpression of ZFP36L2 decreases the endogenous expression of LHR mRNA in a cell line. Therefore, we propose that lack of the physiological down regulation of LHR mRNA levels by ZFP36L2 in the ovaries is associated with anovulation and oocyte meiotic arrest.Fil: Ball, Christopher B.. University of North Carolina; Estados UnidosFil: Rodriguez, Karina F.. National Institutes of Health; Estados UnidosFil: Stumpo, Deborah J.. National Institutes of Health; Estados UnidosFil: Ribeiro Neto, Fernando. National Institutes of Health; Estados UnidosFil: Korach, Kenneth S.. National Institutes of Health; Estados UnidosFil: Blackshear, Perry J.. University of Duke; Estados Unidos. National Institutes of Health; Estados UnidosFil: Birnbaumer, Lutz. National Institutes of Health; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ramos, Silvia B. V.. University of North Carolina; Estados Unido

High-Resolution Sequencing and Modeling Identifies Distinct Dynamic RNA Regulatory Strategies

Cells control dynamic transitions in transcript levels by regulating transcription, processing, and/or degradation through an integrated regulatory strategy. Here, we combine RNA metabolic labeling, rRNA-depleted RNA-seq, and DRiLL, a novel computational framework, to quantify the level; editing sites; and transcription, processing, and degradation rates of each transcript at a splice junction resolution during the LPS response of mouse dendritic cells. Four key regulatory strategies, dominated by RNA transcription changes, generate most temporal gene expression patterns. Noncanonical strategies that also employ dynamic posttranscriptional regulation control only a minority of genes, but provide unique signal processing features. We validate Tristetraprolin (TTP) as a major regulator of RNA degradation in one noncanonical strategy. Applying DRiLL to the regulation of noncoding RNAs and to zebrafish embryogenesis demonstrates its broad utility. Our study provides a new quantitative approach to discover transcriptional and posttranscriptional events that control dynamic changes in transcript levels using RNA sequencing data.National Human Genome Research Institute (U.S.) (Centers for Excellence in Genomics Science 1P50HG006193-01)Howard Hughes Medical InstituteNational Institutes of Health (U.S.) (Pioneer Award)Massachusetts Institute of Technology. William Asbjornsen Albert Memorial FellowshipXerox Fellowship Progra

Stimulation of Polo-Like Kinase 3 mRNA Decay by Tristetraprolin▿ †

Polo-like protein kinase 3 (Plk3) has been proposed to regulate entry into S phase and promote apoptosis in response to oxidative stress. Its mRNA contains three AU-rich elements (AREs) in its 3′ untranslated region (3′-UTR) that can contribute to the rapid degradation of labile transcripts. We investigated the possibility that tristetraprolin (TTP), a tandem CCCH zinc finger protein, could promote the decay of Plk3 transcripts. TTP is known to stimulate the deadenylation and decay of mRNAs possessing one or more copies of the consensus nonamer motif UUAUUUAUU. In stable mouse fibroblast cell lines derived from wild-type and TTP knockout littermates, the decay of Plk3 transcripts after serum stimulation was slowed in the absence of TTP. The specificity of TTP for promoting the degradation of Plk3 was demonstrated by the unaltered decay of Plk3 mRNA in cell lines deficient in the TTP family members ZFP36L1 and ZFP36L2. We also found that the AREs present in the Plk3 transcript were essential for both the binding of TTP to the 3′-UTR and promoting the destruction of target transcripts in cotransfection experiments. The regulation of Plk3 mRNA stability by TTP may influence the control of the cell cycle by this protein kinase

Novel mRNA Targets for Tristetraprolin (TTP) Identified by Global Analysis of Stabilized Transcripts in TTP-Deficient Fibroblasts

Tristetraprolin (TTP) is a tandem CCCH zinc finger protein that was identified through its rapid induction by mitogens in fibroblasts. Studies of TTP-deficient mice and cells derived from them showed that TTP could bind to certain AU-rich elements in mRNAs, leading to increases in the rates of mRNA deadenylation and destruction. Known physiological target mRNAs for TTP include tumor necrosis factor alpha, granulocyte-macrophage colony-stimulating factor, and interleukin-2β. Here we used microarray analysis of RNA from wild-type and TTP-deficient fibroblast cell lines to identify transcripts with different decay rates, after serum stimulation and actinomycin D treatment. Of 250 mRNAs apparently stabilized in the absence of TTP, 23 contained two or more conserved TTP binding sites; nine of these appeared to be stabilized on Northern blots. The most dramatically affected transcript encoded the protein Ier3, recently implicated in the physiological control of blood pressure. The Ier3 transcript contained several conserved TTP binding sites that could bind TTP directly and conferred TTP sensitivity to the mRNA in cell transfection studies. These studies have identified several new, physiologically relevant TTP target transcripts in fibroblasts; these target mRNAs encode proteins from a variety of functional classes

MARCKS modulates radial progenitor placement, proliferation and organization in the developing cerebral cortex

The radial glial cells serve as neural progenitors and as a migratory guide for newborn neurons in the developing cerebral cortex. These functions require appropriate organization and proliferation of the polarized radial glial scaffold. Here, we demonstrate in mice that the myristoylated alanine-rich C-kinase substrate protein (MARCKS), a prominent cellular substrate for PKC, modulates radial glial placement and expansion. Loss of MARCKS results in ectopic collection of mitotically active radial progenitors away from the ventricular zone (VZ) in the upper cerebral wall. Apical restriction of key polarity complexes [CDC42, β-catenin (CTNNB1), N-cadherin (CDH2), myosin IIB (MYOIIB), aPKCζ, LGL, PAR3, pericentrin, PROM1] is lost. Furthermore, the radial glial scaffold in Marcks null cortex is compromised, with discontinuous, non-radial processes apparent throughout the cerebral wall and deformed, bulbous, unbranched end-feet at the basal ends. Further, the density of radial processes within the cerebral cortex is reduced. These deficits in radial glial development culminate in aberrant positioning of neurons and disrupted cortical lamination. Genetic rescue experiments demonstrate, surprisingly, that phosphorylation of MARCKS by PKC is not essential for the role of MARCKS in radial glial cell development. By contrast, the myristoylation domain of MARCKS needed for membrane association is essential for MARCKS function in radial glia. The membrane-associated targeting of MARCKS and the resultant polarized distribution of signaling complexes essential for apicobasal polarity may constitute a critical event in the appropriate placement, proliferation and organization of polarized radial glial scaffold in the developing cerebral cortex

Analysis of the Role of RecQ Helicases in RNAi in Mammals

The identity of mammalian genes involved in RNA interference (RNAi), the targeted sequence-specific mRNA degradation by double-stranded RNA (dsRNA), is poorly defined. Here we report the analysis of mice with null mutations of Wrn, Blm, and RecQ1 genes that are related to Mut-7 and Qde3, two genes essential for RNAi in Caenorhabditis elegans and quelling in Neurospora, respectively. Our results suggest that Wrn, Blm, and RecQ1 are not involved in sequence-specific mRNA degradation in mammals in response to dsRNA, suggesting potential differences in the mammalian RNAi pathway