Role of endogenous antisense RNA in cardiac gene regulation

Full-Length Spatial Transcriptomics Reveals the Unexplored Isoform Diversity of the Myocardium Post-MI

We introduce Single-cell Nanopore Spatial Transcriptomics (scNaST), a software suite to facilitate the analysis of spatial gene expression from second- and third-generation sequencing, allowing to generate a full-length near-single-cell transcriptional landscape of the tissue microenvironment. Taking advantage of the Visium Spatial platform, we adapted a strategy recently developed to assign barcodes to long-read single-cell sequencing data for spatial capture technology. Here, we demonstrate our workflow using four short axis sections of the mouse heart following myocardial infarction. We constructed a de novo transcriptome using long-read data, and successfully assigned 19,794 transcript isoforms in total, including clinically-relevant, but yet uncharacterized modes of transcription, such as intron retention or antisense overlapping transcription. We showed a higher transcriptome complexity in the healthy regions, and identified intron retention as a mode of transcription associated with the infarct area. Our data revealed a clear regional isoform switching among differentially used transcripts for genes involved in cardiac muscle contraction and tissue morphogenesis. Molecular signatures involved in cardiac remodeling integrated with morphological context may support the development of new therapeutics towards the treatment of heart failure and the reduction of cardiac complications.

The role of the X chromosome in infectious diseases

Many infectious diseases in humans present with a sex bias. This bias arises from a combination of environmental factors, hormones and genetics. In this study, we review the contribution of the X chromosome to the genetic factor associated with infectious diseases. First, we give an overview of the X-linked genes that have been described in the context of infectious diseases and group them in four main pathways that seem to be dysregulated in infectious diseases: nuclear factor kappa-B, interleukin 2 and interferon γ cascade, toll-like receptors and programmed death ligand 1. Then, we review the infectious disease associations in existing genome-wide association studies (GWAS) from the GWAS Catalog and the Pan-UK Biobank, describing the main associations and their possible implications for the disease. Finally, we highlight the importance of including the X chromosome in GWAS analysis and the importance of sex-specific analysis.

Mechanisms of Antisense Transcription Initiation with Implications in Gene Expression, Genomic Integrity and Disease Pathogenesis

Non-coding antisense transcripts arise from the strand opposite the sense strand. Over 70% of the human genome generates non-coding antisense transcripts while less than 2% of the genome codes for proteins. Antisense transcripts and/or the act of antisense transcription regulate gene expression and genome integrity by interfering with sense transcription and modulating histone modifications or DNA methylation. Hence, they have significant pathological and physiological relevance. Indeed, antisense transcripts were found to be associated with various diseases including cancer, diabetes, cardiac and neurodegenerative disorders, and, thus, have promising potentials for prognostic and diagnostic markers and therapeutic development. However, it is not clearly understood how antisense transcription is initiated and epigenetically regulated. Such knowledge would provide new insights into the regulation of antisense transcription, and hence disease pathogenesis with therapeutic development. The recent studies on antisense transcription initiation and its epigenetic regulation, which are limited, are discussed here. Furthermore, we concisely describe how antisense transcription/transcripts regulate gene expression and genome integrity with implications in disease pathogenesis and therapeutic development.

Right ventricular long noncoding RNA expression in human heart failure

The expression of long noncoding RNAs (lncRNAs) in human heart failure (HF) has not been widely studied. Using RNA sequencing (RNA-Seq), we compared lncRNA expression in 22 explanted human HF hearts with lncRNA expression in 5 unused donor human hearts. We used Cufflinks to identify isoforms and DESeq to identify differentially expressed genes. We identified the noncoding RNAs by cross-reference to Ensembl release 73 (Genome Reference Consortium human genome build 37) and explored possible functional roles using a variety of online tools. In HF hearts, RNA-Seq identified 84,793 total messenger RNA coding and noncoding different transcripts, including 13,019 protein-coding genes, 2,085 total lncRNA genes, and 1,064 pseudogenes. By Ensembl noncoding RNA categories, there were 48 lncRNAs, 27 pseudogenes, and 30 antisense RNAs for a total of 105 differentially expressed lncRNAs in HF hearts. Compared with donor hearts, HF hearts exhibited differential expression of 7.7% of protein-coding genes, 3.7% of lncRNAs (including pseudogenes), and 2.5% of pseudogenes. There were not consistent correlations between antisense lncRNAs and parent genes and between pseudogenes and parent genes, implying differential regulation of expression. Exploratory in silico functional analyses using online tools suggested a variety of possible lncRNA regulatory roles. By providing a comprehensive profile of right ventricular polyadenylated messenger RNA transcriptome in HF, RNA-Seq provides an inventory of differentially expressed lncRNAs, including antisense transcripts and pseudogenes, for future mechanistic study.

From discovery to function: the expanding roles of long noncoding RNAs in physiology and disease

Long noncoding RNAs (lncRNAs) are a relatively poorly understood class of RNAs with little or no coding capacity transcribed from a set of incompletely annotated genes. They have received considerable attention in the past few years and are emerging as potentially important players in biological regulation. Here we discuss the evolving understanding of this new class of molecular regulators that has emerged from ongoing research, which continues to expand our databases of annotated lncRNAs and provide new insights into their physical properties, molecular mechanisms of action, and biological functions. We outline the current strategies and approaches that have been employed to identify and characterize lncRNAs, which have been instrumental in revealing their multifaceted roles ranging from cis- to trans-regulation of gene expression and from epigenetic modulation in the nucleus to posttranscriptional control in the cytoplasm. In addition, we highlight the molecular and biological functions of some of the best characterized lncRNAs in physiology and disease, especially those relevant to endocrinology, reproduction, metabolism, immunology, neurobiology, muscle biology, and cancer. Finally, we discuss the tremendous diagnostic and therapeutic potential of lncRNAs in cancer and other diseases.

The primary microRNA-208b interacts with Polycomb-group protein, Ezh2, to regulate gene expression in the heart

The Polycomb-group protein, Ezh2, is required for epigenetic gene silencing in the adult heart by unknown mechanism. We investigated the role of Ezh2 and non-coding RNAs in a mouse model of pressure overload using transverse aortic constriction (TAC) attenuated by the prototypical histone deacetylase inhibitor, trichostatin A (TSA). Chromatin immunoprecipitation of TAC and TAC+TSA hearts suggests interaction of Ezh2 and primary microRNA-208b (pri-miR-208b) in the regulation of hypertrophic gene expression. RNAi silencing of pri-miR-208b and Ezh2 validate pri-miR-208b-mediated transcriptional silencing of genes implicated in cardiac hypertrophy including the suppression of the bi-directional promoter (bdP) of the cardiac myosin heavy chain genes. In TAC mouse heart, TSA attenuated Ezh2 binding to bdP and restored antisense β-MHC and α-MHC gene expression. RNA-chromatin immunoprecipitation experiments in TAC hearts also show increased pri-miR-208b dependent-chromatin binding. These results are the first description by which primary miR interactions serve to integrate chromatin modifications and the transcriptional response to distinct signaling cues in the heart. These studies provide a framework for MHC expression and regulation of genes implicated in pathological remodeling of ventricular hypertrophy.

Interplay of chromatin modifications and non-coding RNAs in the heart

Precisely regulated patterns of gene expression are dependent on the binding of transcription factors and chromatin-associated determinants referred to as co-activators and co-repressors. These regulatory components function with the core transcriptional machinery to serve in critical activities to alter chromatin modification and regulate gene expression. While we are beginning to understand that cell-type specific patterns of gene expression are necessary to achieve selective cardiovascular developmental programs, we still do not know the molecular machineries that localize these determinants in the heart. With clear implications for the epigenetic control of gene expression signatures, the ENCODE (Encyclopedia of DNA Elements) Project Consortium determined that about 90% of the human genome is transcribed while only 1-2% of transcripts encode proteins. Emerging evidence suggests that non-coding RNA (ncRNA) serves as a signal for decoding chromatin modifications and provides a potential molecular basis for cell type-specific and promoter-specific patterns of gene expression. The discovery of the histone methyltransferase enzyme EZH2 in the regulation of gene expression patterns implicated in cardiac hypertrophy suggests a novel role for chromatin-associated ncRNAs and is the focus of this article.

Non-coding RNAs: the "dark matter" of cardiovascular pathophysiology

Large-scale analyses of mammalian transcriptomes have identified a significant number of different RNA molecules that are not translated into protein. In fact, the use of new sequencing technologies has identified that most of the genome is transcribed, producing a heterogeneous population of RNAs which do not encode for proteins (ncRNAs). Emerging data suggest that these transcripts influence the development of cardiovascular disease. The best characterized non-coding RNA family is represented by short highly conserved RNA molecules, termed microRNAs (miRNAs), which mediate a process of mRNA silencing through transcript degradation or translational repression. These microRNAs (miRNAs) are expressed in cardiovascular tissues and play key roles in many cardiovascular pathologies, such as coronary artery disease (CAD) and heart failure (HF). Potential links between other ncRNAs, like long non-coding RNA, and cardiovascular disease are intriguing but the functions of these transcripts are largely unknown. Thus, the functional characterization of ncRNAs is essential to improve the overall understanding of cellular processes involved in cardiovascular diseases in order to define new therapeutic strategies. This review outlines the current knowledge of the different ncRNA classes and summarizes their role in cardiovascular development and disease.

Mechanisms of antisense transcription initiation from the 3' end of the GAL10 coding sequence in vivo

In spite of the important regulatory functions of antisense transcripts in gene expression, it remains unknown how antisense transcription is initiated. Recent studies implicated RNA polymerase II in initiation of antisense transcription. However, how RNA polymerase II is targeted to initiate antisense transcription has not been elucidated. Here, we have analyzed the association of RNA polymerase II with the antisense initiation site at the 3' end of the GAL10 coding sequence in dextrose-containing growth medium that induces antisense transcription. We find that RNA polymerase II is targeted to the antisense initiation site at GAL10 by Reb1p activator as well as general transcription factors (e.g., TFIID, TFIIB, and Mediator) for antisense transcription initiation. Intriguingly, while GAL10 antisense transcription is dependent on TFIID, its sense transcription does not require TFIID. Further, the Gal4p activator that promotes GAL10 sense transcription is dispensable for antisense transcription. Moreover, the proteasome that facilitates GAL10 sense transcription does not control its antisense transcription. Taken together, our results reveal that GAL10 sense and antisense transcriptions are regulated differently and shed much light on the mechanisms of antisense transcription initiation.

Long Noncoding RNAs in Cardiac Development and Pathophysiology

Heart function requires sophisticated regulatory networks to orchestrate organ development, physiological responses, and environmental adaptation. Until recently, it was thought that these regulatory networks are composed solely of protein-mediated transcriptional control and signaling systems; consequently, it was thought that cardiac disease involves perturbation of these systems. However, it is becoming evident that RNA, long considered to function primarily as the platform for protein production, may in fact play a major role in most, if not all, aspects of gene regulation, especially the epigenetic processes that underpin organogenesis. These include not only well-validated classes of regulatory RNAs, such as microRNAs, but also tens of thousands of long noncoding RNAs that are differentially expressed across the entire genome of humans and other animals. Here, we review this emerging landscape, summarizing what is known about their functions and their role in cardiac biology, and provide a toolkit to assist in exploring this previously hidden layer of gene regulation that may underpin heart adaptation and complex heart diseases.

HIV-1-encoded antisense RNA suppresses viral replication for a prolonged period

BACKGROUND

Recent evidence proposes a novel concept that mammalian natural antisense RNAs play important roles in cellular homeostasis by regulating the expression of several genes. Identification and characterization of retroviral antisense RNA would provide new insights into mechanisms of replication and pathogenesis. HIV-1 encoded-antisense RNAs have been reported, although their structures and functions remain to be studied. We have tried to identify and characterize antisense RNAs of HIV-1 and their function in viral infection.

RESULTS

Characterization of transcripts of HEK293T cells that were transiently transfected with an expression plasmid with HIV-1NL4-3 DNA in the antisense orientation showed that various antisense transcripts can be expressed. By screening and characterizing antisense RNAs in HIV-1NL4-3-infected cells, we defined the primary structure of a major form of HIV-1 antisense RNAs, which corresponds to a variant of previously reported ASP mRNA. This 2.6 kb RNA was transcribed from the U3 region of the 3' LTR and terminated at the env region in acutely or chronically infected cell lines and acutely infected human peripheral blood mononuclear cells. Reporter assays clearly demonstrated that the HIV-1 LTR harbours promoter activity in the reverse orientation. Mutation analyses suggested the involvement of NF-κΒ binding sites in the regulation of antisense transcription. The antisense RNA was localized in the nuclei of the infected cells. The expression of this antisense RNA suppressed HIV-1 replication for more than one month. Furthermore, the specific knockdown of this antisense RNA enhanced HIV-1 gene expression and replication.

CONCLUSIONS

The results of the present study identified an accurate structure of the major form of antisense RNAs expressed from the HIV-1NL4-3 provirus and demonstrated its nuclear localization. Functional studies collectively demonstrated a new role of the antisense RNA in viral replication. Thus, we suggest a novel viral mechanism that self-limits HIV-1 replication and provides new insight into the viral life cycle.

Genetic approaches for changing the heart and dissecting complex syndromes

The genetic, biochemical and molecular bases of human cardiac disease have been the focus of extensive research efforts for many years. Early animal models of cardiovascular disease used pharmacologic or surgical interventions, or took advantage of naturally occurring genetic abnormalities and the data obtained were largely correlative. The inability to directly alter an organism's genetic makeup and cellular protein content and accurately measure the results of that manipulation precluded rigorous examination of true cause-effect and structure-function relationships. Directed genetic manipulation in the mouse gave researchers the ability to modify and control the mammalian heart's protein content, resulting in the rational design of models that could provide critical links between the mutated or absent protein and disease. Two techniques that have proven particularly useful are transgenesis, which involves the random insertion of ectopic genetic material of interest into a "host" genome, and gene targeting, which utilizes homologous recombination at a pre-selected locus. Initially, transgenesis and gene targeting were used to examine systemic loss-of-function and gain-of-function, respectively, but further refinements in both techniques have allowed for investigations of organ-specific, cell type-specific, developmental stage-sensitive and dose-dependent effects. Genetically engineered animal models of pediatric and adult cardiac disease have proven that, when used appropriately, these tools have the power to extend mere observation to the establishment of true causative proof. We illustrate the power of the general approach by showing how genetically engineered mouse models can define the precise signaling pathways that are affected by the gain-of-function mutation that underlies Noonan syndrome. Increasingly precise and modifiable animal models of human cardiac disease will allow researchers to determine not only pathogenesis, but also guide treatment and the development of novel therapies.

Expression of Na(+)/K(+)-ATPase alpha subunit isoforms in rat salivary glands: occurrence of sense and antisense RNAs of the alpha3 isoform in the sublingual gland

We examined the expression of Na(+)/K(+)-ATPase alpha-subunit isoforms in rat salivary glands by RT-PCR. Isoform alpha1 was expressed strongly in all three major salivary glands. The alpha2 isoform was expressed in both submandibular gland (SMG) and sublingual gland (SLG) but faintly in the parotid gland (PG). The alpha3 was detected only in the SLG, and the alpha3 mRNA in the SLG was 1/8 of its level in the brain. Na(+)/K(+)-ATPase alpha3 isoform in the SLG, was localized predominantly on the basolateral plasma membranes in serous cells by immunohistochemical method. We also found the presence of natural antisense RNA of the alpha3 isoform in rat SLG: the 1st-strand cDNA prepared with gene-specific forward primers targeted to the CDS region and to the promoter region of the alpha3 gene in place of oligo(dT) or gene-specific reverse primers produced reasonable PCR products corresponding to the alpha3 cDNA sequence by the subsequent PCR reaction. Synthesis of the 1st-strand cDNA with the gene-specific forward primers was prevented by RNase digestion of the total RNA preparation, indicating that the PCR products in the RT-PCR system were not due to the contaminated genomic DNA, if any. The alpha3 protein level in rat SLG increased with aging, and levels of both alpha3 mRNA (sense RNA) and alpha3 antisense RNA were higher in SLGs of aged rats than in those of young rats, respectively.

antiCODE: a natural sense-antisense transcripts database

Background

Natural antisense transcripts (NATs) are endogenous RNA molecules that exhibit partial or complete complementarity to other RNAs, and that may contribute to the regulation of molecular functions at various levels. In recent years, large-scale NAT screens in several model organisms have produced much data, but there is no database to assemble all these data. AntiCODE intends to function as an integrated NAT database for this purpose.

Results

This release of antiCODE contains more than 30,000 non-redundant natural sense-antisense transcript pairs from 12 eukaryotic model organisms. In order to provide an integrated NAT research platform, efficient browser, search and Blast functions have been included to enable users to easily access information through parameters such as species, accession number, overlapping patterns, coding potential etc. In addition to the collected information, antiCODE also introduces a simple classification system to facilitate the study of natural antisense transcripts.

Conclusion

Though a few similar databases also dealing with NATs have appeared lately, antiCODE is the most comprehensive among these, comprising almost all currently detected NAT pairs.

The Sp6 locus uses several promoters and generates sense and antisense transcripts

The SP/KLF transcription factor family contains over 25 members sharing a DNA-binding domain composed of three zinc fingers of the C(2)H(2) type. We previously identified the sixth member of the SP subfamily (Sp6). The 5' end of the Sp6 transcript was not cloned and was predicted bioinformatically. A mouse molar tooth cDNA was then isolated differing from the Sp6 sequence by its 5' end, and was named epiprofin. Sp6 and epiprofin are currently used as synonyms. Here, we show that the Sp6 transcript possesses a first exon distinct from the epiprofin one: the Sp6 gene thus uses two promoters, generating two transcript variants which differ in their first exon. Furthermore, we identified an Sp6 opposite strand transcript (Sp6os) and examined, by quantitative RT-PCR experiments, the presence and the abundance of these two transcripts in mouse tissues. We also mapped the mouse locus by FISH to chromosome 11D.

Comparative analysis of cis-encoded antisense RNAs in eukaryotes

Recent large-scale transcriptomic analyses have identified numerous endogenously encoded cis-antisense RNAs that are thought to play important roles in diverse cellular processes although comprehensive comparative studies among multiple species have yet to be performed. To investigate conserved genomic features across various species that may be related to sense-antisense regulation, we performed comparative analysis of approximately 1000-2000 cis-encoded antisense RNA pairs from five model eukaryotes (Homo sapiens, Mus musculus, Drosophila melanogaster, Arabidopsis thaliana, and Oryza sativa). Analysis of overlapping patterns relative to the exon-intron structure revealed that the number of pairs sharing the 3' part of the transcripts was larger than that of the 5'-sharing pairs except in rice. Moreover, most of the well-conserved sense-antisense pairs between human and mouse exhibited 3'-overlaps, suggesting that regulatory mechanisms involving these regions may be important in sense-antisense transcription. Functional classification using Gene Ontology revealed that genes related to catalytic activity, nucleotide binding, DNA metabolism, and mitochondria were preferentially distributed within the set of exon-overlapping sense-antisense genes compared to the non-exon-overlapping group in animals. Despite the numerous sense-antisense pairs identified in human and mouse individually, the number of conserved pairs was extremely small (6.6% of the entire set). Whereas both genes of most of the conserved sense-antisense pairs had protein-coding potential, nearly half of the non-conserved pairs included a non-coding RNA, suggesting that non-coding sense-antisense RNAs may function in species-specific regulatory pathways.

Dynamics of myosin heavy chain gene regulation in slow skeletal muscle: role of natural antisense RNA

The evolutionarily conserved order of the skeletal muscle myosin heavy chain (MHC) genes and their close tandem proximity on the same chromosome are intriguing and may be important for their coordinated regulation. We investigated type II MHC gene regulation in slow-type muscle fibers undergoing a slow to fast MHC transformation in response to inactivity, 7 days after spinal cord isolation (SI) in rats. We examined the transcriptional products of both the sense and antisense strands across the IIa-IIx-IIb MHC gene locus. A strand-specific reverse transcription (RT)-PCR approach was utilized to study the expression of the mRNA, the primary transcript (pre-mRNA), the antisense RNA overlapping the MHC genes, and both the intergenic sense and antisense RNAs. Results showed that the mRNA and pre-mRNA of each MHC had a similar response to SI, suggesting regulation of these genes at the transcriptional level. In addition, we detected previously unknown antisense strand transcription that produced natural antisense transcripts (NATs). RT-PCR mapping of the RNA products revealed that the antisense activity resulted in the formation of three major products: aII, xII, and bII NATs (antisense products of the IIa, IIx, and IIb genes, respectively). The aII NAT begins in the IIa-IIx intergenic region in close proximity to the IIx promoter, extends across the 27-kb IIa MHC gene, and continues to the IIa MHC gene promoter. The expression of the aII NAT was significantly up-regulated in muscles after SI, was negatively correlated with IIa MHC gene expression, and was positively correlated with IIx MHC gene expression. The exact role of the aII NAT is not clear; however, it is consistent with the inhibition of IIa MHC gene transcription. In conclusion, NATs may mediate cross-talk between adjacent genes, which may be essential to the coordinated regulation of the skeletal muscle MHC genes during dynamic phenotype shifts.

The complexity of antisense transcription revealed by the study of developing male germ cells

Computational analyses have identified the widespread occurrence of antisense transcripts in the human and the mouse genome. However, the structure and the origin of the majority of the antisense transcripts are unknown. The presence of antisense transcripts for 19 of 64 differentially expressed genes during mouse spermatogenesis was demonstrated with orientation-specific RT-PCR. These antisense transcripts were derived from a wide variety of origins, including processed sense transcripts, intronic and exonic sequences of a single gene or multiple genes, intergenic sequences, and pseudogenes. They underwent normal and alternative splicing, 5' capping, and 3' polyadenylation, similar to the sense transcripts. There were also antisense transcripts that were not capped and/or polyadenylated. The testicular levels of the sense transcripts were higher than those of the antisense transcripts in all cases, while the relative expression in nontesticular tissues was variable. Thus antisense transcripts have complex origins and structures and the sense and antisense transcripts can be regulated independently.

Characterisation of the mulibrey nanism-associated TRIM37 gene: transcription initiation, promoter region and alternative splicing

The TRIM37 gene encodes a peroxisomal protein of unknown function. Mutations in TRIM37 underlie mulibrey nanism, a rare autosomal recessively inherited disorder with severe growth failure of prenatal onset, constrictive pericardium, hepatomegaly and characteristic dysmorphic features. Eleven mulibrey nanism-associated mutations have been identified. We here characterised TRIM37 further by mapping the transcription initiation site and promoter region as well as by analysing splice variants. By primer extension analysis, several transcription initiation sites were localised to a region between -246 and -373 relative to the ATG codon for translation initiation. Basal promoter activity was mapped within 600 nucleotides upstream from the translation initiation site using promoter-luciferase reporter constructs. Several alternative splice variants of TRIM37 exist in databases. Most of these predict non-functional protein products, are expressed at low levels and are thus likely to be targets for nonsense-mediated mRNA decay. A novel splice variant, TRIM37b, with an alternative termination codon and 3'untranslated region (UTR) transcribed from an exon 16 kb downstream from exon 24, predicts an identical protein product with the previously identified transcript, TRIM37a. As seen by Northern blot analysis and quantitative real-time PCR, both transcripts are highly expressed in testis, whereas in other tissues TRIM37a is prominent. The 3'UTR of the PPM1E gene in the opposite strand overlaps TRIM37b. These data suggest that TRIM37 expression is regulated by several mechanisms: through nonsense surveillance of non-functional transcripts, as well as through 3'UTR regulatory sequences and/or naturally occurring antisense RNAs especially in testis.

Natural antisense transcripts: sound or silence?

Antisense RNA was a rather uncommon term in a physiology environment until short interfering RNAs emerged as the tool of choice to knock down the expression of specific genes. As a consequence, the concept of RNA having regulatory potential became widely accepted. Yet, there is more to come. Computational studies suggest that between 15 and 25% of mammalian genes overlap, giving rise to pairs of sense and antisense RNAs. The resulting transcripts potentially interfere with each other’s processing, thus representing examples of RNA-mediated gene regulation by endogenous, naturally occurring antisense transcripts. Concerns that the large-scale antisense transcription may represent transcriptional noise rather than a gene regulatory mechanism are strongly opposed by recent reports. A relatively small, well-defined group of antisense or noncoding transcripts is linked to monoallelic gene expression as observed in genomic imprinting, X chromosome inactivation, and clonal expression of B and T leukocytes. For the remaining, much larger group of bidirectionally transcribed genes, however, the physiological consequences of antisense transcription as well as the cellular mechanism(s) involved remain largely speculative.

The upstream area of the chicken α-globin gene domain is transcribed in both directions in the same cells

It was demonstrated previously that in erythroid chicken cells an extended upstream area of the alpha-globin gene domain is transcribed in both directions as a part of ggPRX gene and a part of a full domain transcript of the alpha-globin gene domain. Here, we show that both DNA chains of the above-mentioned region are transcribed in the same cells and that the corresponding transcripts coexist in nuclei. The data obtained suggest that cells possess a molecular mechanism which in some cases prevents the formation of dsRNA and subsequent destruction of both transcripts in spite of the presence of complementary RNA chains in the cell nucleus.