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Identifying Co-Expressed lncRNAs Correlated With Traits of Interest in an Animal Model for Metabolic Diseases in Humans.

Nutrigenomics investigates how nutrients modulate gene expression. Among them, fatty acids (FA) play important roles in regulating gene transcription, while long non-coding RNAs (lncRNAs) may be associated with gene regulation and metabolic diseases. This study aimed to analyze the hepatic transcriptome of pigs, a species frequently used as a model for nutrigenomic studies, to identify novel lncRNAs and their potential target genes in response to diets containing different sources of FA. Seventy-two pigs were fed four diets supplemented with 1.5% soybean oil (control), 3% canola oil, 3% fish oil, and 3% soybean oil. RNA sequencing of liver samples was performed to identify novel lncRNAs. Weighted Gene Co-expression Network Analysis (WGCNA) was used to identify modules associated with phenotypic traits related to lipid metabolism and inflammation. Functional enrichment analyses were then conducted to annotate genes within these modules using Gene Ontology (GO) terms and to assess overlap with Quantitative Trait Loci (QTL). The results revealed 106 novel lncRNAs potentially regulating genes associated with lipid metabolism and immune responses in pigs fed diets with different FA sources. These findings enhance understanding of the regulatory role of lncRNAs in pigs and reinforce their relevance as models for human metabolic diseases.

Animals↗

Use of bromovirus RNA3 hybrids to study template specificity in viral RNA amplification.

Brome mosaic virus (BMV) and cowpea chlorotic mottle virus (CCMV) are related positive-strand RNA viruses with genomes divided among RNAs 1, 2, and 3. RNAs 1 and 2 encode the viral RNA replication factors, which share extensive conservation with proteins encoded by the animal alphaviruses and diverse plant viruses. In barley protoplasts, CCMV RNAs 1 and 2 support high but distinguishable amplification of either BMV RNA3 (B3) or CCMV RNA3 (C3), while BMV RNAs 1 and 2 show even greater discrimination, amplifying C3 poorly relative to B3. To identify the cis-acting determinants of these template-specific and virus-specific differences in RNA3 accumulation, we constructed and tested a series of B3/C3 hybrids that exchange in turn the 5',3', and intercistronic noncoding regions, which contain all sequences required in cis for efficient B3 and C3 amplification. Despite suggestive prior in vitro results, the 3' noncoding regions were not the major determinant of the differences in amplification of B3 and C3 in vivo. Rather, 3' exchanges had relatively modest effects and did not transfer the distinctive asymmetry of amplification between B3 and C3. Intercistronic exchanges produced larger effects on RNA3 accumulation and transferred some of the polarized characteristics of the wild-type B3 and C3 behaviors. 5' exchanges revealed context-specific effects showing that the contribution of the B3 5' region to RNA3 amplification is dependent on some other B3 segment or segments. Together with previous results implicating the BMV and CCMV 1a genes in trans-acting discrimination between B3 and C3 (P. Traynor and P. Ahlquist, J. Virol. 64:69-77, 1990), these observations should help to guide studies of protein-RNA interactions governing template specificity in bromovirus RNA replication.

Cloning, Molecular↗

RNA transport in dendrites: a cis-acting targeting element is contained within neuronal BC1 RNA.

In nerve cells, a select group of RNAs has been localized to dendritic domains. Here we have examined dendritic RNA transport in sympathetic neurons in primary culture, using a microinjection protocol with neuronal BC1 RNA and with BC1-derived sequence segments. After cytoplasmic microinjection, full-length BC1 RNA was selectively transported to dendrites; in contrast, control RNAs such as nuclear RNAs and random-sequence irrelevant RNAs remained restricted to cytoplasmic areas proximal to the injection sites. Chimeric RNAs were constructed that contained the full-length BC1 sequence inserted upstream or downstream of the coding regions of nondendritic mRNAs. After microinjection, such chimeric RNAs were specifically targeted to dendrites; microinjected corresponding nonchimeric mRNAs were not. Dendritic transport of BC1 RNA was rapid: the average dendritic delivery rate within the first hour after microinjection was 242 +/- 25 microm/hr. Whereas a 5'-BC1 segment of 62 nucleotides was transported to dendrites to extents and at levels similar to full-length BC1 RNA, a 3'-BC1 segment of 60 nucleotides did not exit injected somata to any significant degree. A cis-acting dendritic targeting element is thus contained in the 5' part of neuronal BC1 RNA. These results demonstrate that mechanisms exist in neurons for fast and specific transport of selected RNAs to dendrites.

Animals↗

A cluster of latently expressed genes in Kaposi's sarcoma-associated herpesvirus.

Infection with Kaposi's sarcoma-associated herpesvirus (KSHV) is closely associated with Kaposi's sarcoma (KS) and primary effusion lymphoma, with viral genomes present in a latent state in the majority of tumor cells. Here we describe a cluster of latently expressed viral genes whose mRNAs are generated from a common promoter. Two mRNAs in this region encode the latency-associated nuclear antigen, the product of open reading frame 73 (ORF73). The larger RNA, of 5.8 kb, is an unspliced transcript that includes ORF72 and -71 at its 3' end; it initiates at nucleotides (nt) 127880 to 127886 from a promoter lacking recognizable TATA elements. A less abundant mRNA, of 5.4 kb, is a variant of this transcript, in which 336 nt of 5' noncoding information has been removed by RNA splicing. A third, more abundant RNA is generated from the same promoter region via splicing from the common splice donor at nt 127813 to an acceptor 5' to ORF72; this transcript is the presumed mRNA for ORF72, which encodes the viral cyclin D homolog. All three RNAs are 3' coterminal. In situ hybridization analysis with probes that can detect all three transcripts shows that the RNAs are detectable in a large fraction of BCBL-1 cells prior to lytic induction and in >70% of KS spindle cells in primary KS tumors. This confirms that these transcripts are indeed latent RNAs and suggests a role for their products in viral persistence and/or KSHV-associated proliferation.

Alternative Splicing↗

Coding sequences enhance internal initiation of translation by hepatitis A virus RNA in vitro.

Hepatitis A virus (HAV), unlike other picornaviruses, has a slow-growth phenotype in permissive cell lines and in general does not induce host cell cytopathology. Although there are no published reports of productive infection of HeLa cells by HAV, HAV RNA appears to be readily translated in HeLa cells when transcribed by T7 RNA polymerase provided by a recombinant vaccinia virus. The 5' noncoding region of HAV was fused to poliovirus (PV) coding sequences to determine the effect on translation efficiency in HeLa cell extracts in vitro. Conditions were optimized for utilization of the HAV internal ribosome entry segment (IRES). Transcripts from chimeric constructs fused precisely at the initiation codon were translated very poorly. However, chimeric RNAs which included 114 or more nucleotides from the HAV capsid coding sequences downstream of the initiation codon were translated much more efficiently than those lacking these sequences, making HAV-directed translation efficiency similar to that directed by the PV IRES. Sixty-six nucleotides were insufficient to confer increased translation efficiency. The most 5'-terminal HAV 138 nucleotides, previously determined to be upstream of the IRES, had an inhibitory effect on translation efficiency. Constructs lacking these terminal sequences, or those in which the PV 5'-terminal sequences replaced those from HAV, translated three- to fourfold better than those with the intact HAV 5'-terminal end.

Cell Extracts↗

Replication of in vitro tobravirus recombinants shows that the specificity of template recognition is determined by 5' non-coding but not 3' non-coding sequences.

Natural recombinant tobacco rattle tobravirus (TRV) isolates contain sequences from a different tobravirus, pea early browning virus (PEBV). To characterize the sequence requirements for viable recombinant formation hybrid cDNA clones of RNA2 of PEBV and TRV were assembled. Inclusion of 320 nt from the 5' terminus of PEBV or 335 nt from the 5' terminus of TRV in the hybrid RNAs was sufficient to permit their replication by, respectively, PEBV RNA1 or TRV RNA1 regardless of the origin of the 3' terminal region. However, PEBV RNA1 but not TRV RNA1 was sometimes able to support low level replication of RNA2 containing the heterologous 5' terminal region. In vitro translation of PEBV transcripts containing 5' noncoding region deletions supported the hypothesis that in vivo the PEBV coat protein (CP) is expressed from a subgenomic RNA and that, therefore, in the recombinants the CP subgenomic promoter probably is recognized by the replicase of the heterologous virus.

Cloning, Molecular↗

Mutational analysis of the pseudoknot region in the 3' noncoding region of tobacco mosaic virus RNA.

The approximately 200-nucleotide-long 3'-terminal noncoding region of tobacco mosaic virus (TMV) RNA contains a tRNA-like structure and, in its immediate upstream region, three consecutive pseudoknots, each of which is composed of two double-helical segments. To elucidate the biological functions of the pseudoknot region, we constructed several deletion mutant TMV-L (a tomato strain) RNAs by using an in vitro transcription system and tested their ability to multiply in both tobacco plants and protoplasts. When deletions were introduced just downstream of the termination codon of the coat protein gene in the 5'-to-3' direction progressively, five of six double-helical segments were dispensable for viral multiplication, indicating that the pseudoknot structures are not essential for multiplication. However, extension of the deletion into the central pseudoknot region resulted in reduction in viral multiplication, accompanied by loss of development of mosaic symptoms on systemic tobacco plants. Cessation of multiplication was observed when the sequence involved in formation of double-helical segment I just upstream of the tRNA-like structure was deleted irrespective of the start point and extent of deletion. Point mutations that destabilized double-helical segment I resulted in a loss or great reduction of viral multiplication, whereas the double mutants in which the double helix was restored by additional compensating base substitutions restored multiplication to nearly the wild-type level. Thus, double-helical segment I just upstream of the tRNA-like structure is a structural feature essential for viral multiplication.

Base Sequence↗

Secondary structure analysis of adenovirus tripartite leader.

RNA secondary structure analysis was performed to understand the translation function of the adenovirus tripartite leader, a 200-nucleotide 5' noncoding region found on all late viral mRNAs. The tripartite leader facilitates the translation of viral mRNAs at late but not early times after infection and eliminates the normal requirement for the eukaryotic initiation factor 4F or cap binding protein complex. Secondary structures were determined by probing 5' or 3' end-labeled tripartite leader RNAs under nondenaturing conditions with various single strand-specific nucleases, and the information was used to generate a potential model structure. The resulting structure is attractive since it may explain the unusual translation behavior conferred by the tripartite leader. We demonstrate that the first leader segment is predominantly single-stranded, a property consistent with the ability to enhance translation and provide independence from cap binding protein complex. In contrast, the remaining two leader segments form a moderately stable base-paired structure, except for a large hairpin loop. To confirm these findings, the secondary structure of the tripartite leader was also probed when it was attached to a large segment of a messenger RNA and was found to be very similar to that of the individual leader RNA. These findings suggest several possible mechanisms to account for the translation activity of the tripartite leader.

Adenoviridae↗

The 5'-terminal 32 basepairs conserved between genome segments A and B contain a major promoter element of infectious bursal disease virus.

The regions of the infectious bursal disease virus (IBDV) genome with regulatory function are not known. In the present study, progressively deleted lengths of the 5' noncoding region of segment A were constructed in pGL3 vectors having SV40 enhancer or promoter, and a luciferase (LUC) reporter gene. Transient transfections of the constructs made in a promoter-less pGL3-Enhancer vector when transfected in Vero cells and the lysates assayed for LUC expression, allowed the localization of maximal activity to the 32-nucleotide stretch (precursor polyprotein ORF positions -131 to -100), which is highly conserved at the 5' end of both genome segments. This fragment, when evaluated in parallel in an enhancer-less pGL3-Promoter vector demonstrated no activity. To determine if this region is recognized by IBDV replicative proteins, we engineered modifications in an enhancer-less pGL3-Promoter vector where the terminal 32-bp fragment, the full-length noncoding region, or the noncoding region with the 32-bp fragment deleted was positioned in either the plus-sense or the minus-sense orientation immediately downstream of the SV40 promoter and upstream of the LUC gene. Transfections of these constructs in IBDV-infected and uninfected Vero cells resulted in the endogenous generation of recombinant viral-LUC RNAs containing the 5' terminal viral RNA sequences in either the plus-sense or the minus-sense orientation. LUC assays of the infected cell lysates showed up-regulated expression of LUC only with constructs containing the 32-bp fragment in the minus-sense orientation. Deletion of this 32-bp fragment abolished such LUC expression. We therefore conclude that the 5'-terminal 32 base pairs of genomic segment A contain a major promoter element in IBDV. In addition, our results show that IBDV replicative proteins recognize and transcribe single-stranded RNA in vivo.

Animals↗

Nonallelic members of the cytochrome c multigene family of the rat may arise through different messenger RNAs.

We determined the nucleotide sequences of three nonallelic cytochrome c genes (from recombinant clones Ch4A-RC5, 6 and 8) isolated from the rat cytochrome c gene family. In contrast with a fourth gene (from Ch4A-RC4), which has an intron and correctly encodes rat cytochrome c, these three appear to be pseudogenes and resemble mRNA molecules in two respects: they are all missing the intron of clone 4, and sequence homology with clone 4 in their 3' noncoding regions abruptly ends at two different A-rich tracts reminiscent of poly(A) tails. We also detect three cytochrome c mRNAs of sizes 1400, 1100 and 700 nucleotides in several tissues of the adult rat. The size differences among the mRNAs can be accounted for by length heterogeneity in their 3' noncoding regions. Two of the 3' ends map to the two points where the mRNA-like genes diverge from clone 4 at poly(A) tracts. Furthermore, short direct repeats flank the genes of clones 5, 6 and 8 at the positions where their sequences diverge. The observations suggest that these members of the cytochrome c multigene family may arise through insertion into the genome of DNA copies of cytochrome c mRNAs.

Animals↗

Detection of enteroviruses and rhinoviruses in clinical specimens by PCR and liquid-phase hybridization.

A sensitive method based on PCR followed by liquid-phase hybridization for detection of enterovirus and rhinovirus RNAs in clinical specimens and cell culture supernatants is described. RNA was extracted from stool samples, throat swabs, nasopharyngeal aspirates, cerebrospinal fluid, urine, and plasma with a commercial phenol-guanidinium-chloroform reagent and purified on a polysulfone membrane, on which the reverse transcriptase reaction was also done. Two sets of oligonucleotide primers from the 5' noncoding region of picornaviruses were selected for DNA amplification of 153-bp (enterovirus) and 120-bp (rhinovirus) regions. Double-stranded amplicons were digested into single strands with T7 gene 6 exonuclease and quantitated by an assay using a europium-labeled probe, streptavidin- and biotinylated probe-coated microtitration wells, and time-resolved fluorometry. The sensitivity of the assay was about one template molecule when purified coxsackievirus A9 RNA was used. All enterovirus prototype strains, except echoviruses 22 and 23, and clinical isolates grown in cell culture or suckling mice were strongly positive by the enterovirus PCR-hybridization, as were selected prototype strains and untyped isolates of rhinoviruses by the rhinovirus PCR-hybridization. In a series of 100 clinical specimens tested, the results for 92 agreed with virus culture results. The detection method described will be useful in etiopathogenic studies on enteroviruses and rhinoviruses.

Animals↗

Transcription and RNA replication of tacaribe virus genome and antigenome analogs require N and L proteins: Z protein is an inhibitor of these processes.

Tacaribe virus (TV), the prototype of the New World group of arenaviruses, comprises a single phylogenetic lineage together with four South American pathogenic producers of hemorrhagic disease. The TV genome consists of two single-stranded RNA segments called S and L. A reconstituted transcription-replication system based on plasmid-supplied TV-like RNAs and TV proteins was established. Plasmid expression was driven by T7 RNA polymerase supplied by a recombinant vaccinia virus. Plasmids were constructed to produce TV S segment analogs containing the negative-sense copy of chloramphenicol acetyltransferase (CAT) flanked at the 5' and 3' termini by sequences corresponding to those of the 5' and 3' noncoding regions of the S genome (minigenome) or the S antigenome (miniantigenome). In cells expressing N and L proteins, input minigenome or miniantigenome produced, respectively, encapsidated miniantigenome or minigenome which in turn produced progeny minigenome or progeny miniantigenome. Both minigenome and miniantigenome in the presence of N and L mediated transcription, which was analyzed as CAT expression. Coexpression of the small RING finger Z (p11) protein was highly inhibitory to both transcription and replication mediated by the minigenome or the miniantigenome. The effect depended on synthesis of Z protein rather than on plasmid or the RNA and was not ascribed to decreased amounts of plasmid-supplied template or proteins (N or L). N and L proteins were sufficient to support full-cycle RNA replication of a plasmid-supplied S genome analog in which CAT replaced the N gene. Replication of this RNA was also inhibited by Z expression.

Arenaviruses, New World↗

Demonstration of functional requirement of polypyrimidine tract-binding protein by SELEX RNA during hepatitis C virus internal ribosome entry site-mediated translation initiation.

Polypyrimidine tract-binding protein (PTB) has been previously shown to physically interact with the hepatitis C virus (HCV) RNA genome at its 5'- and 3'-noncoding regions. Using high affinity SELEX RNA molecules, we present evidence for the functional requirement of PTB during HCV internal ribosome entry site (IRES)-controlled translation initiation. This study was carried out in rabbit reticulocyte translation lysates in which the HCV IRES-driven reporter RNA was introduced along with the PTB-specific SELEX RNA molecules. The SELEX RNAs specifically inhibited the HCV IRES function in the context of mono- and dicistronic mRNAs. The cap-dependent translation of a reporter (chloramphenicol acetyltransferase) RNA or naturally capped brome mosaic virus RNA, however, was not affected by the presence of SELEX during in vitro translation assays. The SELEX-mediated inhibition of the HCV IRES is shown to be relieved by the addition of recombinant human PTB in an add-back experiment. The in vivo requirement of PTB was further confirmed by cotransfection of Huh7 cells with reporter RNA and PTB-specific SELEX RNA. The HCV IRES activity was inhibited by the SELEX RNA in these cells, but not by an unrelated control RNA. Together, these results demonstrate the functional requirement of cellular PTB in HCV translation and further support the feasible use of SELEX RNA strategy in demonstrating the functional relevance of cellular protein(s) in complex biological processes.

Base Sequence↗

Profilaggrin is a major epidermal calcium-binding protein.

Profilaggrin is a major highly phosphorylated protein component of the keratohyalin granules of mammalian epidermis. It contains 10 to 12 tandemly repeated filaggrin units and is processed into the intermediate filament-associated protein filaggrin by specific dephosphorylation and proteolysis during terminal differentiation of the epidermal cells. Later, filaggrin itself is degraded to free amino acids that participate in maintenance of epidermal flexibility. The present paper describes the structural organization of the 5' region of the human profilaggrin gene as well as the amino terminus of the profilaggrin protein. The primary profilaggrin transcript consists of three exons and two introns. The first exon (exon I) is only 54 bp and is untranslated. The coding sequences are distributed between exon II (159 bp) and exon III, which contains the information for 10 to 12 filaggrin repeats (972 bp each) and the 3' noncoding sequences. A very large intron separates exons I and II. The combination of a very short exon I with an unusually long intron 1 makes the structure of the profilaggrin gene unique among the epidermally expressed genes investigated so far. Comparison of the expression patterns revealed by primer extension and RNase protection analysis of foreskin epidermal and cultured keratinocyte RNAs suggests that alternately spliced messages, which are different from profilaggrin mRNA, are transcribed from the profilaggrin gene system at earlier stages of epidermal differentiation. The amino terminus of profilaggrin exhibits a significant homology to the small calcium-binding S100-like proteins. It contains two alpha-helical regions, termed EF-hands, that bind calcium in vitro. This is the first example of functional calcium-binding domains fused to a structural protein. We suggest that in addition to its role in filament aggregation and the maintenance of epidermal flexibility, profilaggrin may play an important role in the differentiation of the epidermis by autoregulating its own processing in a calcium-dependent manner or by participating in the transduction of calcium signal in epidermal cells.

Amino Acid Sequence↗

Localization of gurken RNA in Drosophila oogenesis requires elements in the 5' and 3' regions of the transcript.

During Drosophila oogenesis, signaling between the germline and the soma leads to the establishment of polarity in the egg and embryo. This process involves the interaction of gurken (grk), a TGFalpha-like protein, with torpedo (top), the Drosophila EGF receptor (Egfr). In early stage egg chambers, grk RNA is present predominantly along the posterior cortex of the oocyte, and in mid stage egg chambers, the grk transcript becomes tightly localized to the future dorsal anterior corner of the oocyte. This localization of grk RNA restricts the distribution of Gurken protein and is critical in defining both the anterior-posterior and dorsal-ventral axes of the egg. We have determined the genomic sequence of the grk gene. By testing the requirement of various fragments of grk RNA in the localization process, we find localization signals present in both the 5' and 3' regions of the gene. Sequences in the 5' noncoding region allow for accumulation of the transcript within the oocyte in early stage egg chambers, while signals in the coding region and the 3'UTR are necessary for localization in mid to late stage egg chambers. Active translation is not required for localization of the grk RNA. The mechanism of gurken RNA localization, therefore, differs from that of other localized RNAs studied to date.

3' Untranslated Regions↗

Near identity of 3- RNA secondary structure in bromoviruses and cucumber mosaic virus.

The 3- terminal sequences of RNAs 1, 2, 3 and 4 from each of the three bromoviruses (brome mosaic, cowpea chlorotic mottle and broad bean mottle viruses) and also from cucumber mosaic virus display interviral sequence similarity in addition to strong intraviral homology. Interviral similarity is much more evident when RNA secondary, rather than primary, structures are compared. The last 190 bases of the various RNAs can fold into strikingly similar, extensively base-paired secondary structures whose common features are supported by RNA structure mapping. The extreme 3' end of each viral RNA can base-pair in two distinct configurations. Bromovirus RNA 3s each contain an unusually accessible internal oligo(A) sequence which, in brome mosaic virus at least, is located in the intercistronic noncoding region. Functional implications of these structural features are discussed.

Base Sequence↗

Splice site requirement for the efficient accumulation of polyoma virus late mRNAs.

Polyoma virus late nuclear primary transcripts are giant and heterogeneous, containing tandem repeats of the late strand of the circular viral genome. Late pre-mRNA processing involves the splicing of noncoding 'leader' exons to each other (removing genome-length introns), with the joining of the last leader to a coding 'body' exon. We have constructed a number of mutants blocked only in leader-leader splicing, or blocked in both leader-leader and leader-body splicing. We examined the accumulation of both nuclear and cytoplasmic late-strand RNAs in NIH3T3 cells. Consistent with our previous results, mutants lacking the 3' splice site of the late leader (leader-leader splicing blocked) showed a 10-20 fold defect in late RNA accumulation. Mutants which lacked the leader 5' splice site (leader-body splicing blocked) had a more profound defect, exhibiting virtually no late-strand cytoplasmic or nuclear RNA. This result was unexpected as a substantial proportion of wild type late cytoplasmic messages are unspliced. A mutant with no intron, but having functional 3' and 5' splice sites bordering the leader exon, is capable of producing large amounts of unspliced late mRNA. This demonstrates that an excisable intron is not a requirement for late mRNA accumulation. The accumulation of polyoma late mRNAs requires the presence of leader exons bordered by functional 3' and 5' splice sites, whether or not these sites are used during pre-mRNA processing.

Base Sequence↗

Dosage compensation: an intertwined world of RNA and chromatin remodelling.

Dosage compensation mechanisms in flies and mammals provide an exquisite example of chromatin associated RNAs in chromosome-wide transcription regulation. Recent progress shows that chromatin modifications are also closely linked to these processes. Concerted action of the RNA/chromatin-modifying enzymes may play a crucial role in determining transcriptional output. Furthermore, non-coding RNAs appear to play a dual role, being targeting modules as well as encoding for target sites for complex recognition.

Animals↗