Descripción: Insertion of factor MudJ in the intergenic region between divergent genes yrfF and yrfE, at centisome 76 in the genome of Salmonella enterica serovar Typhimurium LT2, confers the characteristics recently described for mucM mutants, i.e. mucoidy and resistance to mecillinam. Cloning of the intergenic region plus either the yrfF or the yrfE gene in a multicopy plasmid showed that only the plasmid carrying the yrfF gene complemented mucM mutants, thus suggesting that mucM mutations are in fact yrfF mutations. A null yrfF mutation obtained by insertion of a kanamycin cassette into the yrfF open reading frame (yrfF28::Kan) produced abortive colonies when transduced to a wild-type strain but was normally accepted by rcsB, rcsC or yojN strains. Neither mutations preventing synthesis of the capsular exopolysaccharide colanic acid (cps, galE) nor rcsA mutations, which reduce expression of cps genes, conferred tolerance to the lethal yrfF28::Kan mutation. Spontaneous suppressor mutations arose very frequently in abortive yrfF28::Kan colonies, and all of them affected either rcsC, yojN, or rcsB genes. Thus, the lethal effect caused by inactivation of gene yrfF appears to be mediated by a function that is dependent on the rcsC-yojN-rcsB phosphorelay system but does not involve synthesis of colanic acid. © 2003 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

Descripción: Genomes contain the necessary information to ensure that genes are expressed in the right place, at the right time, and with the proper rate. Metazoan developmental genes often possess long stretches of DNA flanking their coding sequences and/or large introns which contain elements that influence gene expression. Most of these regulatory elements are relatively small and can be studied in isolation. For example, transcriptional enhancers, the elements that generate the expression pattern of a gene, have been traditionally studied with reporter constructs in transgenic animals. These studies have provided and will provide invaluable insights into enhancer evolution and function. However, this experimental approach has its limits; often, enhancer elements do not faithfully recapitulate native expression patterns. This fact suggests that additional information in cis-regulatory regions modulates the activity of enhancers and other regulatory elements. Indeed, recent studies have revealed novel functional aspects at the level of whole cis-regulatory regions. First, the discovery of "shadow enhancers." Second, the ubiquitous interactions between cis-regulatory elements. Third, the notion that some cis-regulatory regions may not function in a modular manner. Last, the effect of chromatin conformation on cis-regulatory activity. In this article, I describe these recent findings and discuss open questions in the field. © 2012 Wiley Periodicals, Inc.

Descripción: Understanding the genetic architecture of any quantitative trait requires identifying the genes involved in its expression in different environmental conditions. This goal can be achieved by mutagenesis screens in genetically tractable model organisms such as Drosophila melanogaster. Temperature during ontogenesis is an important environmental factor affecting development and phenotypic variation in holometabolous insects. In spite of the importance of phenotypic plasticity and genotype by environment interaction (GEI) for fitness related traits, its genetic basis has remained elusive. In this context, we analyzed five different adult morphological traits (face width, head width, thorax length, wing size and wing shape) in 42 co-isogenic single P-element insertional lines of Drosophila melanogaster raised at 17°C and 25°C. Our analyses showed that all lines differed from the control for at least one trait in males or females at either temperature. However, no line showed those differences for all traits in both sexes and temperatures simultaneously. In this sense, the most pleiotropic candidate genes were CG34460, Lsd-2 and Spn. Our analyses also revealed extensive genetic variation for all the characters mostly indicated by strong GEIs. Further, our results indicate that GEIs were predominantly explained by changes in ranking order in all cases suggesting that a moderate number of genes are involved in the expression of each character at both temperatures. Most lines displayed a plastic response for at least one trait in either sex. In this regard, P-element insertions affecting plasticity of a large number of traits were associated to the candidate genes Btk29A, CG43340, Drak and jim. Further studies will help to elucidate the relevance of these genes on the morphogenesis of different body structures in natural populations of D. melanogaster. © 2013 Carreira et al.

Descripción: Background: Alzheimer's disease (AD) is characterized by a neurodegenerative progression that alters cognition. On a phenotypical level, cognition is evaluated by means of the MiniMental State Examination (MMSE) and the post-morten examination of Neurofibrillary Tangle count (NFT) helps to confirm an AD diagnostic. The MMSE evaluates different aspects of cognition including orientation, short-term memory (retention and recall), attention and language. As there is a normal cognitive decline with aging, and death is the final state on which NFT can be counted, the identification of brain gene expression biomarkers from these phenotypical measures has been elusive. Methodology/Principal Findings: We have reanalysed a microarray dataset contributed in 2004 by Blalock et al. of 31 samples corresponding to hippocampus gene expression from 22 AD subjects of varying degree of severity and 9 controls. Instead of only relying on correlations of gene expression with the associated MMSE and NFT measures, and by using modern bioinformatics methods based on information theory and combinatorial optimization, we uncovered a 1,372-probe gene expression signature that presents a high-consensus with established markers of progression in AD. The signature reveals alterations in calcium, insulin, phosphatidylinositol and wnt-signalling. Among the most correlated gene probes with AD severity we found those linked to synaptic function, neurofilament bundle assembly and neuronal plasticity. Conclusions/Significance: A transcription factors analysis of 1,372-probe signature reveals significant associations with the EGR/KROX family of proteins, MAZ, and E2F1. The gene homologous of EGR1, zif268, Egr-1 or Zenk, together with other members of the EGR family, are consolidating a key role in the neuronal plasticity in the brain. These results indicate a degree of commonality between putative genes involved in AD and prion-induced neurodegenerative processes that warrants further investigation. © 2010 Go ́mez Ravetti et al.

Descripción: Background: Subtractive hybridization methods are valuable tools for identifying differentially regulated genes in a given tissue avoiding redundant sequencing of clones representing the same expressed genes, maximizing detection of low abundant transcripts and thus, affecting the efficiency and cost effectiveness of small scale cDNA sequencing projects aimed to the specific identification of useful genes for breeding purposes. The objective of this work is to evaluate alternative strategies to high-throughput sequencing projects for the identification of novel genes differentially expressed in sunflower as a source of organ-specific genetic markers that can be functionally associated to important traits. Results: Differential organ-specific ESTs were generated from leaf, stem, root and flower bud at two developmental stages (R1 and R4). The use of different sources of RNA as tester and driver cDNA for the construction of differential libraries was evaluated as a tool for detection of rare or low abundant transcripts. Organ-specificity ranged from 75 to 100% of non-redundant sequences in the different cDNA libraries. Sequence redundancy varied according to the target and driver cDNA used in each case. The R4 flower cDNA library was the less redundant library with 62% of unique sequences. Out of a total of 919 sequences that were edited and annotated, 318 were non-redundant sequences. Comparison against sequences in public databases showed that 60% of non-redundant sequences showed significant similarity to known sequences. The number of predicted novel genes varied among the different cDNA libraries, ranging from 56% in the R4 flower to 16 % in the R1 flower bud library. Comparison with sunflower ESTs on public databases showed that 197 of non-redundant sequences (60%) did not exhibit significant similarity to previously reported sunflower ESTs. This approach helped to successfully isolate a significant number of new reported sequences putatively related to responses to important agronomic traits and key regulatory and physiological genes. Conclusions: The application of suppressed subtracted hybridization technology not only enabled the cost effective isolation of differentially expressed sequences but it also allowed the identification of novel sequences in sunflower from a relative small number of analyzed sequences when compared to major sequencing projects. © 2003 Fernández et al; licensee BioMed Central Ltd.

Descripción: The stress response involves complex physiological mechanisms that maximize behavioral efficacy during attack or defense and is highly conserved in all vertebrates. Key mediators of the stress response are pituitary hormones encoded by the proopiomelanocortin gene (POMC). Despite conservation of physiological function and expression pattern of POMC in all vertebrates, phylogenetic footprinting analyses at the POMC locus across vertebrates failed to detect conserved noncoding sequences with potential regulatory function. To investigate whether ortholog POMC promoters from extremely distant vertebrates are functionally conserved, we used 5′-flanking sequences of the teleost fish Tetraodon nigroviridis POMCα gene to produce transgenic mice. Tetraodon POMCα promoter targeted reporter gene expression exclusively to mouse pituitary cells that normally express Pomc. Importantly, transgenic expression in mouse corticotrophs was increased after adrenalectomy. To understand how conservation of precise gene expression mechanisms coexists with great sequence divergence, we investigated whether very short elements are still conserved in all vertebrate POMC promoters. Multiple local sequence alignments that consider phylogenetic relationships of ortholog regions identified a unique 10-bp motif GTGCTAA(T/G)CC that is usually present in two copies in POMC 5′-flanking sequences of all vertebrates. Underlined nucleotides represent totally conserved sequences. Deletion of these paired motifs from Tetraodon POMCα promoter markedly reduced its transcriptional activity in a mouse corticotropic cell line and in pituitary POMC cells of transgenic mice. In mammals, the conserved motifs correspond to reported binding sites for pituitary-specific nuclear proteins that participate in POMC transcriptional regulation. Together, these results demonstrate that mechanisms that participate in pituitary-specific and hormonally regulated expression of POMC have been preserved since mammals and teleosts diverged from a common ancestor 450 million years ago despite great promoter sequence divergence. Copyright © 2007 by The Endocrine Society.

Descripción: The transcription factor TCERG1 (also known as CA150) associates with RNA polymerase II holoenzyme and alters the elongation efficiency of reporter transcripts. TCERG1 is also found as a component of highly purified spliceosomes and has been implicated in splicing. To elucidate the function of TCERG1, we used short interfering RNA-mediated knockdown followed by en masse gene expression analysis to identify its cellular targets. Analysis of data from HEK293 and HeLa cells identified high confidence targets of TCERG1. We found that targets of TCERG1 were enriched in microRNA-binding sites, suggesting the possibility of post-transcriptional regulation. Consistently, reverse transcription-PCR analysis revealed that many of the changes observed upon TCERG1 knockdown were because of differences in alternative mRNA processing of the 3′-untranslated regions. Furthermore, a novel computational approach, which can identify alternatively processed events from conventional microarray data, showed that TCERG1 led to widespread alterations in mRNA processing. These findings provide the strongest support to date for a role of TCERG1 in mRNA processing and are consistent with proposals that TCERG1 couples transcription and processing. © 2008 by The American Society for Biochemistry and Molecular Biology, Inc.

Descripción: The role of GAs in promoting seed germination is well known and experiments with seeds from different species have suggested the requirement of de novo synthesis of GAs upon imbibition for germination. There are also strong indications that the enhancement of GA synthesis is part of the mechanism through which environmental signals (i.e. light) induce germination. Since along the GA biosynthetic pathway, oxidation at C-20 carried out by GA 20-oxidases is thought to be a site of regulation, a cDNA clone encoding a GA 20-oxidase was isolated from embryos of sorghum (SbGA 20ox). Expression analysis of this gene in embryos within imbibed caryopses with low dormancy showed detectable amounts of the specific mRNA early upon incubation, increasing thereafter. In contrast, it remained barely detectable in embryos from dormant caryopses. Changes in endogenous GA4 levels were in agreement with those of SbGA 20ox mRNA, suggesting that GA production might be regulated differentially at the level of transcription of this gene. The expression of SbGA 20ox was enhanced in incubated embryos isolated from either type of caryopses, illustrating a physiological control exerted by the surrounding seed tissues on gene expression. The results also show that ABA leads to a suppression of transcription of this gene.

Descripción: Hypoxia-Inducible Factor (HIF) prolyl hydroxylase domains (PHDs) have been proposed to act as sensors that have an important role in oxygen homeostasis. In the presence of oxygen, they hydroxylate two specific prolyl residues in HIF-α polypeptides, thereby promoting their proteasomal degradation. So far, however, the developmental consequences of the inactivation of PHDs in higher metazoans have not been reported. Here, we describe novel loss-of-function mutants of fatiga, the gene encoding the Drosophila PHD oxygen sensor, which manifest growth defects and lethality. We also report a null mutation in dHIF-α/sima, which is unable to adapt to hypoxia but is fully viable in normoxic conditions. Strikingly, loss-of-function mutations of sima rescued the developmental defects observed in fatiga mutants and enabled survival to adulthood. These results indicate that the main functions of Fatiga in development, including control of cell size, involve the regulation of dHIF/Sima. © 2005 European Molecular Biology Organization.

Descripción: Our view of the structure and function of the interphase nucleus has changed drastically in recent years. It is now widely accepted that the nucleus is a well organized and highly compartmentalized organelle and that this organization is intimately related to nuclear function. In this context, chromatin-initially considered a randomly entangled polymer-has also been shown to be structurally organized in interphase and its organization was found to be very important to gene regulation. Relevant and not completely answered questions are how chromatin organization is achieved and what mechanisms are responsible for changes in the positions of chromatin loci in the nucleus. A significant advance in the field resulted from tagging chromosome sites with bacterial operator sequences, and visualizing these tags using green fluorescent protein fused with the appropriate repressor protein. Simultaneously, fluorescence imaging techniques evolved significantly during recent years, allowing observation of the time evolution of processes in living specimens. In this context, the motion of the tagged locus was observed and analyzed to extract quantitative information regarding its dynamics. This review focuses on recent advances in our understanding of chromatin dynamics in interphase with the emphasis placed on the information obtained from single-particle tracking (SPT) experiments. We introduce the basis of SPT methods and trajectory analysis, and summarize what has been learnt by using this new technology in the context of chromatin dynamics. Finally, we briefly describe a method of SPT in a two-photon excitation microscope that has several advantages over methods based on conventional microscopy and review the information obtained using this novel approach to study chromatin dynamics. © 2008 Springer.

Descripción: Subclinical low-grade systemic inflammation has been associated with obesity, insulin resistance and metabolic syndrome (MS). Recent studies have highlighted the role of gut microbiota in these disorders. The toll-like receptor 4 (TLR4) plays a key role in the innate immune response activation. We studied two polymorphisms (+3725G/C and 11350G/C) in the 3′ untranslated region (3′UTR) of the TLR4 gene that may alter its expression and their association with metabolic disorders related to systemic inflammation. We cloned the 3′UTR into a luciferase reporter system and compared wild-type 3′UTR (WT) and +3725C variant (MUT) constructs luciferase activities. MUT construct reduced the reporter gene activity by 30% compared to WT (P = 0.0001). To evaluate the association between these polymorphisms with biochemical and clinical overweight related variables, we conducted a population cross-sectional study in 966 men of Argentine general population. Considering smoking as a confounding variable that causes systemic inflammation, we studied these possible effects in both, smokers and nonsmokers. The 11350G/C polymorphism was not detected in our sample whereas the CC genotype of +3725 polymorphism was associated with lean subjects (p = 0.011) and higher Adiponectin levels (p = 0.021). Subjects without any NCEP/ATP III MS component were associated with this genotype as well (p = 0.001). These results were strengthened in nonsmokers, in which CC genotype was associated with lean subjects (p = 0.003) and compared with G carriers showed significantly lower BMI (25.53 vs. 28.60 kg/m2; p = 0.023) and waist circumference (89.27 vs. 97.51 cm; p = 0.025). None of these associations were found in smokers. These results showed that +3725C variant has a functional effect down-regulating gene expression and it could be considered as a predictive factor against overweight, particularly in nonsmokers. Considering the role of TLR4 in inflammation, these findings would suggest that the presence of +3725C variant could predict a lower prevalence of chronic metabolic disorders. © 2012 Penas-Steinhardt et al.

Descripción: Genes required for xanthan polysaccharide synthesis (xps) are clustered in a DNA region of 13.5 kb in the chromosome of Xanthomonas campestris. Plasmid pCHC3 containing a 12.4-kb insert of xps genes has been suggested to include a gene involved in the pyruvylation of xanthan gum (N. E. Harding, J. M. Cleary, D. K. Cabanas, I. G. Rosen, and K. S. Kang, J. Bacteriol. 169:2854-2861, 1987). An essential step toward understanding the biosynthesis of xanthan gum and to enable genetic manipulation of xanthan structure is the determination of the biochemical function encoded by the xps genes. On the basis of biochemical characterization of an X. campestris mutant which produces pyruvate-free xanthan gum, complementation studies, and heterologous expression, we have identified the gene coding for the ketal pyruvate transferase (kpt) enzyme. This gene was located on a 1.4-kb BamHI fragment of pCHC3 and cloned in the broad-host-range cloning vector pRK404. An X. campestris kpt mutant was constructed by mini-Mu(Tet(r)) mutagenesis of the cloned gene and then by recombination of the mutation into the chromosome of the wild-type strain.

Descripción: MAGE-A genes are a subfamily of the melanoma antigen genes (MAGEs), whose expression is restricted to tumor cells of different origin and normal tissues of the human germline. Although the specific function of individual MAGE-A proteins is being currently explored, compelling evidence suggest their involvement in the regulation of different pathways during tumor progression. We have previously reported that MageA2 binds histone deacetylase (HDAC)3 and represses p53-dependent apoptosis in response to chemotherapeutic drugs. The promyelocytic leukemia (PML) tumor suppressor is a regulator of p53 acetylation and function in cellular senescence. Here, we demonstrate that MageA2 interferes with p53 acetylation at PML-nuclear bodies (NBs) and with PMLIV-dependent activation of p53. Moreover, a fraction of MageA2 colocalizes with PML-NBs through direct association with PML, and decreases PMLIV sumoylation through an HDAC-dependent mechanism. This reduction in PML post-translational modification promotes defects in PML-NBs formation. Remarkably, we show that in human fibroblasts expressing RasV12 oncogene, MageA2 expression decreases cellular senescence and increases proliferation. These results correlate with a reduction in NBs number and an impaired p53 response. All these data suggest that MageA2, in addition to its anti-apoptotic effect, could have a novel role in the early progression to malignancy by interfering with PML/p53 function, thereby blocking the senescence program, a critical barrier against cell transformation. © 2012 Macmillan Publishers Limited. All rights reserved.

Descripción: The proopiomelanocortin gene (POMC) encodes several bioactive peptides, including adrenocorticotropin hormone, α-, β-, and γ-melanocyte-stimulating hormone, and the opioid peptide β-endorphin, which play key roles in vertebrate physiology. In the human, mouse, and chicken genomes, there is only one POMC gene. By searching public genome projects, we have found that Tetraodon (Tetraodon nigroviridis), Fugu (Takifugu rubripes), and zebrafish (Danio rerio) possess two POMC genes, which we called POMCα and POMCβ, and we present phylogenetic and mapping evidence that these paralogue genes originated in the whole-genome duplication specific to the teleost lineage over 300 MYA. In addition, we present evidence for two types of subfunction partitioning between the paralogues. First, in situ hybridization experiments indicate that the expression domains of the ancestral POMC gene have been subfunctionalized in Tetraodon, with POMCα expressed in the nucleus lateralis tuberis of the hypothalamus, as well as in the rostral pars distalis and pars intermedia (PI) of the pituitary, whereas POMCβ is expressed in the preoptic area of the brain and weakly in the pituitary PI. Second, POMCβ genes have a β-endorphin segment that lacks the consensus opioid signal and seems to be under neutral evolution in tetraodontids, whereas POMCα genes possess well-conserved peptide regions. Thus, POMC paralogues have experienced subfunctionalization of both expression and peptide domains during teleost evolution. The study of regulatory regions of fish POMC genes might shed light on the mechanisms of enhancer partitioning between duplicate genes, as well as the roles of POMC-derived peptides in fish physiology.

Descripción: Xanthan is an industrially important exopolysaccharide produced by the phytopathogenic, gram-negative bacterium Xanthomonas campestris pv. campestris. It is composed of polymerized pentasaccharide repeating malts which are assembled by the sequential addition of glucose-1-phosphate, glucose, mannose, glucuronic acid, and mannose on a polyprenol phosphate carrier (L. Ielpi, R. O. Couso, and M. A. Dankert, J. Bacteriol. 175:2490- 2500, 1993). A cluster of 12 genes in a region designated xpsI or gum has been suggested to encode proteins involved in the synthesis and polymerization of the lipid intermediate. However, no experimental evidence supporting this suggestion has been published. In this work, from the biochemical analysis of a defined set of X. campestris gum mutants, we report experimental data for assigning functions to the products of the gum genes. We also show that the first step in the assembly of the lipid-linked intermediate is severely affected by the combination of certain gum and non- gum mutations. In addition, we provide evidence that the C-terminal domain of the gumD gene product is sufficient for its glucosyl-1-phosphate transferase activity. Finally, we found that alterations in the later stages of xanthan biosynthesis reduce the aggressiveness of X. campestris against the plant.

Descripción: Despite considerable progress in our understanding of the interplay between immune and endocrine systems, the role of thyroid hormones and their receptors in the control of adaptive immunity is still uncertain. Here, we investigated the role of thyroid hormone receptor (TR) β 1 signaling in modulating dendritic cell (DC) physiology and the intracellular mechanisms underlying these immunoregulatory effects. Exposure of DCs to triiodothyronine (T 3 ) resulted in a rapid and sustained increase in Akt phosphorylation independently of phosphatidylinositol 3-kinase activation, which was essential for supporting T 3 -induced DC maturation and interleukin (IL)-12 production. This effect was dependent on intact TRβ 1 signaling as small interfering RNA-mediated silencing of TRβ 1 expression prevented T 3 -induced DC maturation and IL-12 secretion as well as Akt activation and IκB-ε degradation. In turn, T 3 up-regulated TRβ 1 expression through mechanisms involving NF-κB, suggesting an autocrine regulatory loop to control hormone-dependent TRβ 1 signaling. These findings were confirmed by chromatin immunoprecipitation analysis, which disclosed a new functional NF-κB consensus site in the promoter region of the TRB1 gene. Thus, a T 3 -induced NF-κB-dependent mechanism controls TRβ 1 expression, which in turn signals DCs to promote maturation and function via an Akt-dependent but PI3K-independent pathway. These results underscore a novel unrecognized target that regulates DC maturation and function with critical implications in immunopathology at the crossroads of the immune-endocrine circuits. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.

Descripción: Efferent inhibition of cochlear hair cells is mediated by α9α10 nicotinic cholinergic receptors (nAChRs) functionally coupled to calcium-activated, small conductance (SK2) potassium channels. Before the onset of hearing, efferent fibers transiently make functional cholinergic synapses with inner hair cells (IHCs). The retraction of these fibers after the onset of hearing correlates with the cessation of transcription of the Chrna10 (but not the Chrna9) gene in IHCs. To further analyze this developmental change, we generated a transgenic mice whose IHCs constitutively express α10 into adulthood by expressing the α10 cDNA under the control of the Pou4f3 gene promoter. In situ hybridization showed that the α10 mRNA is expressed in IHCs of 8-week-old transgenic mice, but not in wild-type mice. Moreover, this mRNA is translated into a functional protein, since IHCs from P8-P10 α10 transgenic mice backcrossed to a Chrna10 -/- background (whose IHCs have no cholinergic function) displayed normal synaptic and acetylcholine (ACh)-evoked currents in patch-clamp recordings. Thus, the α10 transgene restored nAChR function. However, in the α10 transgenic mice, no synaptic or ACh-evoked currents were observed in P16-18 IHCs, indicating developmental down-regulation of functional nAChRs after the onset of hearing, as normally observed in wild-type mice. The lack of functional ACh currents correlated with the lack of SK2 currents. These results indicate that multiple features of the efferent postsynaptic complex to IHCs, in addition to the nAChR subunits, are down-regulated in synchrony after the onset of hearing, leading to lack of responses to ACh. © 2009 Association for Research in Otolaryngology.

Descripción: Chromatin structure is an important factor in the functional coupling between transcription and mRNA processing, not only by regulating alternative splicing events, but also by contributing to exon recognition during constitutive splicing. We observed that depolarization of neuroblastoma cell membrane potential, which triggers general histone acetylation and regulates alternative splicing, causes a concentration of SR proteins in nuclear speckles. This prompted us to analyze the effect of chromatin structure on splicing factor distribution and dynamics. Here, we show that induction of histone hyper-acetylation results in the accumulation in speckles of multiple splicing factors in different cell types. In addition, a similar effect is observed after depletion of the heterochromatic protein HP1α, associated with repressive chromatin. We used advanced imaging approaches to analyze in detail both the structural organization of the speckle compartment and nuclear distribution of splicing factors, as well as studying direct interactions between splicing factors and their association with chromatin in vivo. The results support a model where perturbation of normal chromatin structure decreases the recruitment efficiency of splicing factors to nascent RNAs, thus causing their accumulation in speckles, which buffer the amount of free molecules in the nucleoplasm. To test this, we analyzed the recruitment of the general splicing factor U2AF65 to nascent RNAs by iCLIP technique, as a way to monitor early spliceosome assembly. We demonstrate that indeed histone hyper-acetylation decreases recruitment of U2AF65 to bulk 3′ splice sites, coincident with the change in its localization. In addition, prior to the maximum accumulation in speckles, ~20% of genes already show a tendency to decreased binding, while U2AF65 seems to increase its binding to the speckle-located ncRNA MALAT1. All together, the combined imaging and biochemical approaches support a model where chromatin structure is essential for efficient co-transcriptional recruitment of general and regulatory splicing factors to pre-mRNA. © 2012 Schor et al.

Descripción: The proopiomelanocortin gene (POMC) is expressed in the pituitary gland and the ventral hypothalamus of all jawed vertebrates, producing several bioactive peptides that function as peripheral hormones or central neuropeptides, respectively. We have recently determined that mouse and human POMC expression in the hypothalamus is conferred by the action of two 5′ distal and unrelated enhancers, nPE1 and nPE2. To investigate the evolutionary origin of the neuronal enhancer nPE2, we searched available vertebrate genome databases and determined that nPE2 is a highly conserved element in placentals, marsupials, and monotremes, whereas it is absent in nonmammalian vertebrates. Following an in silico paleogenomic strategy based on genome-wide searches for paralog sequences, we discovered that opossum and wallaby nPE2 sequences are highly similar to members of the superfamily of CORE-short interspersed nucleotide element (SINE) retroposons, in particular to MAR1 retroposons that are widely present in marsupial genomes. Thus, the neuronal enhancer nPE2 originated from the exaptation of a CORE-SINE retroposon in the lineage leading to mammals and remained under purifying selection in all mammalian orders for the last 170 million years. Expression studies performed in transgenic mice showed that two nonadjacent nPE2 subregions are essential to drive reporter gene expression into POMC hypothalamic neurons, providing the first functional example of an exapted enhancer derived from an ancient CORE-SINE retroposon. In addition, we found that this CORE-SINE family of retroposons is likely to still be active in American and Australian marsupial genomes and that several highly conserved exonic, intronic and intergenic sequences in the human genome originated from the exaptation of CORESINE retroposons. Together, our results provide clear evidence of the functional novelties that transposed elements contributed to their host genomes throughout evolution. © 2007 Santangelo et al.