Differential fates of introns in gene expression due to global alternative splicing.

The discovery of introns over four decades ago revealed a new vision of genes and their interrupted arrangement. Throughout the years, it has appeared that introns play essential roles in the regulation of gene expression. Unique processing of excised introns through the formation of lariats suggests a widespread role for these molecules in the structure and function of cells. In addition to rapid destruction, these lariats may linger on in the nucleus or may even be exported to the cytoplasm, where they remain stable circular RNAs (circRNAs). Alternative splicing (AS) is a source of diversity in mature transcripts harboring retained introns (RI-mRNAs). Such RNAs may contain one or more entire retained intron(s) (RIs), but they may also have intron fragments resulting from sequential excision of smaller subfragments via recursive splicing (RS), which is characteristic of long introns. There are many potential fates of RI-mRNAs, including their downregulation via nuclear and cytoplasmic surveillance systems and the generation of new protein isoforms with potentially different functions. Various reports have linked the presence of such unprocessed transcripts in mammals to important roles in normal development and in disease-related conditions. In certain human neurological-neuromuscular disorders, including myotonic dystrophy type 2 (DM2), frontotemporal dementia/amyotrophic lateral sclerosis (FTD/ALS) and Duchenne muscular dystrophy (DMD), peculiar processing of long introns has been identified and is associated with their pathogenic effects. In this review, we discuss different mechanisms involved in the processing of introns during AS and the functions of these large sections of the genome in our biology.

Thermal adaptation of mRNA secondary structure: stability versus lability.

Macromolecular function commonly involves rapidly reversible alterations in three-dimensional structure (conformation). To allow these essential conformational changes, macromolecules must possess higher order structures that are appropriately balanced between rigidity and flexibility. Because of the low stabilization free energies (marginal stabilities) of macromolecule conformations, temperature changes have strong effects on conformation and, thereby, on function. As is well known for proteins, during evolution, temperature-adaptive changes in sequence foster retention of optimal marginal stability at a species' normal physiological temperatures. Here, we extend this type of analysis to messenger RNAs (mRNAs), a class of macromolecules for which the stability-lability balance has not been elucidated. We employ in silico methods to determine secondary structures and estimate changes in free energy of folding (ΔGfold) for 25 orthologous mRNAs that encode the enzyme cytosolic malate dehydrogenase in marine mollusks with adaptation temperatures spanning an almost 60 °C range. The change in free energy that occurs during formation of the ensemble of mRNA secondary structures is significantly correlated with adaptation temperature: ΔGfold values are all negative and their absolute values increase with adaptation temperature. A principal mechanism underlying these adaptations is a significant increase in synonymous guanine + cytosine substitutions with increasing temperature. These findings open up an avenue of exploration in molecular evolution and raise interesting questions about the interaction between temperature-adaptive changes in mRNA sequence and in the proteins they encode.

Construction of ceRNA network to identify the lncRNA and mRNA related to non-small cell lung cancer.

BACKGROUND: Non-small cell lung cancer (NSCLC) harms human health, but its pathogenesis remains unclear. We wish to provide more molecular therapeutic targets for NSCLC. METHODS: The NSCLC tissue and normal tissue samples were screened for genetic comparison in the TCGA database. The predicted lncRNA and mRNA in BEAS2B and A549 cells were detected. RESULTS: Volcano plot displayed differentially expressed lncRNAs and mRNAs in adjacent tissues and NSCLC tissues. The survival curve showed that the lncRNA and mRNA had a significant impact on the patient's survival. The results of GO term enrichment analysis indicated that mRNA functions were enriched in cell cycle-related pathways. In the ceRNA interaction network, 13 lncRNAs and 20 miRNAs were found to have an interactive relationship. Finally, 3 significantly different lncRNAs (LINC00968, lnc-FAM92A-9 and lnc-PTGFR-1) and 6 mRNAs (CTCFL, KRT5, LY6D, TMEM, GBP6, and TMEM179) with potential therapeutic significance were screened out. And the cell experiment verified our results. CONCLUSION: We screened out clinically significant 3 lncRNAs and 6 mRNAs involved in the ceRNA network, which were the key to our future research on the treatment of NSCLC.

Identification of cell cycle as the critical pathway modulated by exosome-derived microRNAs in gallbladder carcinoma.

Gallbladder cancer (GBC), the most common malignancy in the biliary tract, is highly lethal malignant due to seldomly specific symptoms in the early stage of GBC. This study aimed to identify exosome-derived miRNAs mediated competing endogenous RNAs (ceRNA) participant in GBC tumorigenesis. A total of 159 differentially expressed miRNAs (DEMs) was identified as exosome-derived miRNAs, contains 34 upregulated exo-DEMs and 125 downregulated exo-DEMs based on the expression profiles in GBC clinical samples downloaded from the Gene Expression Omnibus database with the R package. Among them, 2 up-regulated exo-DEMs, hsa-miR-125a-3p and hsa-miR-4647, and 5 down-regulated exo-DEMs, including hsa-miR-29c-5p, hsa-miR-145a-5p, hsa-miR-192-5p, hsa-miR-194-5p, and hsa-miR-338-3p, were associated with the survival of GBC patients. Results of the gene set enrichment analysis showed that the cell cycle-related pathways were activated in GBC tumor tissues, mainly including cell cycle, M phase, and cell cycle checkpoints. Furthermore, the dysregulated ceRNA network was constructed based on the lncRNA-miRNA-mRNA interactions using miRDB, TargetScan, miRTarBase, miRcode, and starBase v2.0., consisting of 27 lncRNAs, 6 prognostic exo-DEMs, and 176 mRNAs. Together with prognostic exo-DEMs, the STEAP3-AS1/hsa-miR-192-5p/MAD2L1 axis was identified, suggesting lncRNA STEAP3-AS1, might as a sponge of exosome-derived hsa-miR-192-5p, modulates cell cycle progression via affecting MAD2L1 expression in GBC tumorigenesis. In addition, the biological functions of genes in the ceRNA network were also annotated by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes. Our study promotes exploration of the molecular mechanisms associated with tumorigenesis and provide potential targets for GBC diagnosis and treatment.

Hepatocyte Nuclear Factor 4 alpha 2 Messenger RNA Reprograms Liver-Enriched Transcription Factors and Functional Proteins in End-Stage Cirrhotic Human Hepatocytes.

The only definitive therapy for end-stage liver disease is whole-organ transplantation. The success of this intervention is severely limited by the complexity of the surgery, the cost of patient care, the need for long-term immunosuppression, and the shortage of donor organs. In rodents and humans, end-stage degeneration of hepatocyte function is associated with disruption of the liver-specific transcriptional network and a nearly complete loss of promoter P1-driven hepatocyte nuclear factor 4-alpha (P1-HNF4α) activity. Re-expression of HNF4α2, the predominant P1-HNF4α, reinstates the transcriptional network, normalizes the genes important for hepatocyte function, and reverses liver failure in rodents. In this study, we tested the effectiveness of supplementary expression of human HNF4α2 messenger RNA (mRNA) in primary human hepatocytes isolated from explanted livers of patients who underwent transplant for end-stage irreversibly decompensated liver failure (Child-Pugh B, C) resulting from alcohol-mediated cirrhosis and nonalcoholic steatohepatitis. Re-expression of HNF4α2 in decompensated cirrhotic human hepatocytes corrects the disrupted transcriptional network and normalizes the expression of genes important for hepatocyte function, improving liver-specific protein expression. End-stage liver disease in humans is associated with both loss of P1-HNF4α expression and failure of its localization to the nucleus. We found that while HNF4α2 re-expression increased the amount of P1-HNF4α protein in hepatocytes, it did not alter the ability of hepatocytes to localize P1-HNF4α to their nuclei. Conclusion: Re-expression of HNF4α2 mRNA in livers of patients with end-stage disease may be an effective therapy for terminal liver failure that would circumvent the need for organ transplantation. The efficacy of this strategy may be enhanced by discovering the cause for loss of nuclear P1-HNF4α localization in end-stage cirrhosis, a process not found in rodent studies.

Integrated microRNA and transcriptome profiling reveal key miRNA-mRNA interaction pairs associated with seed development in Tartary buckwheat (Fagopyrum tataricum).

BACKGROUND: Tartary buckwheat seed development is an extremely complex process involving many gene regulatory pathways. MicroRNAs (miRNAs) have been identified as the important negative regulators of gene expression and performed crucial regulatory roles in various plant biological processes. However, whether miRNAs participate in Tartary buckwheat seed development remains unexplored. RESULTS: In this study, we first identified 26 miRNA biosynthesis genes in the Tartary buckwheat genome and described their phylogeny and expression profiling. Then we performed small RNA (sRNA) sequencing for Tartary buckwheat seeds at three developmental stages to identify the miRNAs associated with seed development. In total, 230 miRNAs, including 101 conserved and 129 novel miRNAs, were first identified in Tartary buckwheat, and 3268 target genes were successfully predicted. Among these miRNAs, 76 exhibited differential expression during seed development, and 1534 target genes which correspond to 74 differentially expressed miRNAs (DEMs) were identified. Based on integrated analysis of DEMs and their targets expression, 65 miRNA-mRNA interaction pairs (25 DEMs corresponding to 65 target genes) were identified that exhibited significantly opposite expression during Tartary buckwheat seed development, and 6 of the miRNA-mRNA pairs were further verified by quantitative real-time polymerase chain reaction (qRT-PCR) and ligase-mediated rapid amplification of 5' cDNA ends (5'-RLM-RACE). Functional annotation of the 65 target mRNAs showed that 56 miRNA-mRNA interaction pairs major involved in cell differentiation and proliferation, cell elongation, hormones response, organogenesis, embryo and endosperm development, seed size, mineral elements transport, and flavonoid biosynthesis, which indicated that they are the key miRNA-mRNA pairs for Tartary buckwheat seed development. CONCLUSIONS: Our findings provided insights for the first time into miRNA-mediated regulatory pathways in Tartary buckwheat seed development and suggested that miRNAs play important role in Tartary buckwheat seed development. These findings will be help to study the roles and regulatory mechanism of miRNAs in Tartary buckwheat seed development.

Comprehensive analysis of ceRNA networks reveals prognostic lncRNAs related to immune infiltration in colorectal cancer.

BACKGROUND: Competing endogenous RNA (ceRNA) represents a class of RNAs (e.g., long noncoding RNAs [lncRNAs]) with microRNA (miRNA) binding sites, which can competitively bind miRNA and inhibit its regulation of target genes. Increasing evidence has underscored the involvement of dysregulated ceRNA networks in the occurrence and progression of colorectal cancer (CRC). The purpose of this study was to construct a ceRNA network related to the prognosis of CRC and further explore the potential mechanisms that affect this prognosis. METHODS: RNA-Seq and miRNA-Seq data from The Cancer Genome Atlas (TCGA) were used to identify differentially expressed lncRNAs (DElncRNAs), microRNAs (DEmiRNAs), and mRNAs (DEmRNAs), and a prognosis-related ceRNA network was constructed based on DElncRNA survival analysis. Subsequently, pathway enrichment, Pearson correlation, and Gene Set Enrichment Analysis (GSEA) were performed to determine the function of the genes in the ceRNA network. Gene Expression Profiling Interactive Analysis (GEPIA) and immunohistochemistry (IHC) were also used to validate differential gene expression. Finally, the correlation between lncRNA and immune cell infiltration in the tumor microenvironment was evaluated based on the CIBERSORT algorithm. RESULTS: A prognostic ceRNA network was constructed with eleven key survival-related DElncRNAs (MIR4435-2HG, NKILA, AFAP1-AS1, ELFN1-AS1, AC005520.2, AC245884.8, AL354836.1, AL355987.4, AL591845.1, LINC02038, and AC104823.1), 54 DEmiRNAs, and 308 DEmRNAs. The MIR4435-2HG- and ELFN1-AS1-associated ceRNA subnetworks affected and regulated the expression of the COL5A2, LOX, OSBPL3, PLAU, VCAN, SRM, and E2F1 target genes and were found to be related to prognosis and tumor-infiltrating immune cell types. CONCLUSIONS: MIR4435-2HG and ELFN1-AS1 are associated with prognosis and tumor-infiltrating immune cell types and could represent potential prognostic biomarkers or therapeutic targets in colorectal carcinoma.

Identification of circRNA-miRNA-mRNA Regulatory Network in Bladder Cancer by Integrated Analysis.

INTRODUCTION: Bladder cancer (BC) is a common malignant tumor in the urinary system with high mortality and recurrence rates. This study sought to identify crucial circular RNAs (circRNAs) associated with BC. METHODS: The mRNA, miRNA, and circRNA expression profiles of BC were downloaded from GEO database. The differentially expressed mRNAs (DEmRNAs), miRNAs (DEmiRNAs), and circRNAs (DEcircRNAs) were identified using bioinformatics method. Combining circRNA-miRNA pairs with miRNA-mRNA pairs, the competing endogenous RNA (ceRNA; DEcircRNA-DEmi-RNA-DEmRNA) regulatory network was constructed. Functional annotation of host gene of DEcircRNAs and DEmRNAs in ceRNA regulatory network were performed. qRT-PCR validation was performed. RESULTS: A total of 4,003 DEmRNAs, 25 DEmiRNAs, and 119 DEcircRNAs were obtained. The ceRNA network contained 18 circRNA-miRNA pairs and 699 mi-RNA-mRNA pairs, including 17 circRNAs, 4 miRNAs, and 624 mRNAs. Functional annotation of DEmRNAs in ceRNA regulatory network revealed that these DEmRNAs were significantly enriched in glycerolipid metabolism, p53 signaling pathway, and oocyte meiosis. Except for hsa_circ_0028173, expression of the others in the qRT-PCR results was consistent with that in our integrated analysis, generally. CONCLUSION: We speculate that hsa_circ_0008035/hsa-miR-107/MSRB3 and hsa_circ_0028173/hsa-miR-338-3p/TPX2/GATA3 interaction pairs may play a vital role in BC.

Short prolactin isoforms are expressed in photoreceptors of canine retinas undergoing retinal degeneration.

Prolactin (PRL) hormone functions as a pleiotropic cytokine with a protective role in the retina. We recently identified by transcriptome profiling that PRL is one of the most highly upregulated mRNAs in the retinas of mutant rcd1 (PDE6B) and xlpra2 (RPGR) dogs at advanced stages of photoreceptor disease. In the present study, we have identified the expression of a short PRL isoform that lacks exon 1 in canine retinas and analyzed the time-course of expression and localization of this isoform in the retinas of these two models. Using laser capture microdissection to isolate RNA from each of the retinal cellular layers, we found by qPCR that this short PRL isoform is expressed in photoreceptors of degenerating retinas. We confirmed by in situ hybridization that its expression is localized to the outer nuclear layer and begins shortly after the onset of disease at the time of peak photoreceptor cell death in both models. PRL protein was also detected only in mutant dog retinas. Our results call for further investigations into the role of this novel PRL isoform in retinal degeneration.

Emerging Role for Linear and Circular Spermine Oxidase RNAs in Skeletal Muscle Physiopathology.

Skeletal muscle atrophy is a pathological condition so far without effective treatment and poorly understood at a molecular level. Emerging evidence suggest a key role for circular RNAs (circRNA) during myogenesis and their deregulation has been reported to be associated with muscle diseases. Spermine oxidase (SMOX), a polyamine catabolic enzyme plays a critical role in muscle differentiation and the existence of a circRNA arising from SMOX gene has been recently identified. In this study, we evaluated the expression profile of circular and linear SMOX in both C2C12 differentiation and dexamethasone-induced myotubes atrophy. To validate our findings in vivo their expression levels were also tested in two murine models of amyotrophic lateral sclerosis: SOD1G93A and hFUS+/+, characterized by progressive muscle atrophy. During C2C12 differentiation, linear and circular SMOX show the same trend of expression. Interestingly, in atrophy circSMOX levels significantly increased compared to the physiological state, in both in vitro and in vivo models. Our study demonstrates that SMOX represents a new player in muscle physiopathology and provides a scientific basis for further investigation on circSMOX RNA as a possible new therapeutic target for the treatment of muscle atrophy.

Identification of a competing endogenous RNA axis related to gastric cancer.

Competing endogenous RNA (ceRNA) pathways play pivotal roles in the formation and progression of gastric cancer (GC). Employing multi-omics analysis, we sought to identify a ceRNA network associated with GC progression. We analyzed3Gene Expression Omnibus datasets as well as data from The Cancer Genome Atlas to identify genes that were differentially expressed in GC tissues. A total of 84 upregulated genes and 106 downregulated genes were found. Enrichment analysis indicated that some pathways were strongly linked with tumor formation and progression. We also screened hub genes to establish a lncRNA-miRNA-mRNA network. We ultimately identified 8 hub genes, 6 key miRNAs and 4 key lncRNAs that interact within a common ceRNA network. Correlation analysis and in vitro experiments were conducted to verify the regulatory effect of the ceRNA network in GC. A knockdown assay confirmed that the DLGAP1-AS1/miR-203a-3p/THBS2 axis is a ceRNA network involved in GC progression. In this study, we elucidated the role of the DLGAP1-AS1/miR-203a-3p/THBS2 ceRNA network in the progression of GC. These molecules maybe evaluated as therapeutic targets and prognostic biomarkers for GC.

A possible universal role for mRNA secondary structure in bacterial translation revealed using a synthetic operon.

In bacteria, translation re-initiation is crucial for synthesizing proteins encoded by genes that are organized into operons. The mechanisms regulating translation re-initiation remain, however, poorly understood. We now describe the ribosome termination structure (RTS), a conserved and stable mRNA secondary structure localized immediately downstream of stop codons, and provide experimental evidence for its role in governing re-initiation efficiency in a synthetic Escherichia coli operon. We further report that RTSs are abundant, being associated with 18%-65% of genes in 128 analyzed bacterial genomes representing all phyla, and are selectively depleted when translation re-initiation is advantageous yet selectively enriched so as to insulate translation when re-initiation is deleterious. Our results support a potentially universal role for the RTS in controlling translation termination-insulation and re-initiation across bacteria.

Ribosome profiling reveals a functional role for autophagy in mRNA translational control.

Autophagy promotes protein degradation, and therefore has been proposed to maintain amino acid pools to sustain protein synthesis during metabolic stress. To date, how autophagy influences the protein synthesis landscape in mammalian cells remains unclear. Here, we utilize ribosome profiling to delineate the effects of genetic ablation of the autophagy regulator, ATG12, on translational control. In mammalian cells, genetic loss of autophagy does not impact global rates of cap dependent translation, even under starvation conditions. Instead, autophagy supports the translation of a subset of mRNAs enriched for cell cycle control and DNA damage repair. In particular, we demonstrate that autophagy enables the translation of the DNA damage repair protein BRCA2, which is functionally required to attenuate DNA damage and promote cell survival in response to PARP inhibition. Overall, our findings illuminate that autophagy impacts protein translation and shapes the protein landscape.

Dissecting MicroRNA-mRNA Regulatory Networks Underlying Sulfur Assimilation and Cadmium Accumulation in Poplar Leaves.

The process of cadmium (Cd) accumulation and detoxification under different sulfur levels remains largely unknown in woody plants. To investigate the physiological and transcriptomic regulation mechanisms of poplars in response to different sulfate (S) supply levels and Cd exposure, we exposed Populus deltoides saplings to one of the low, moderate and high S levels together with either 0 or 50 µM Cd. Cd accumulation was decreased in low S-treated poplar leaves, and it tended to be increased in high S-supplied leaves under the Cd exposure condition. Sulfur nutrition was deficient in low S-supplied poplars, and it was improved in high S-treated leaves. Cd exposure resulted in lower sulfur level in the leaves supplied with moderate S, it exacerbated a Cd-induced sulfur decrease in low S-treated leaves and it caused a higher sulfur concentration in high S-supplied leaves. In line with the physiological changes, a number of mRNAs and microRNAs (miRNAs) involved in Cd accumulation and sulfur assimilation were identified and the miRNA-mRNA networks were dissected. In the networks, miR395 and miR399 members were identified as hub miRNAs and their targets were ATP sulfurylase 3 (ATPS3) and phosphate 2 (PHO2), respectively. These results suggest that Cd accumulation and sulfur assimilation are constrained by low and enhanced by high S supply, and Cd toxicity is aggravated by low and relieved by high S in poplar leaves, and that miRNA-mRNA regulatory networks play pivotal roles in sulfur-mediated Cd accumulation and detoxification in Cd-exposed poplars.

Identification of a circRNA-miRNA-mRNA network to explore the effects of circRNAs on pathogenesis and treatment of spinal cord injury.

AIMS: Many studies have demonstrated that circRNAs are closely associated with human diseases. Nonetheless, the potential mechanism by which circRNAs impacts spinal cord injury (SCI) is not fully understood. The aim of this study was to explore the regulatory roles of circRNAs in SCI. MAIN METHODS: The sequencing data of circRNA, miRNA and mRNA were obtained from Gene Expression Omnibus (GEO) datasets. Candidates were identified to construct a circRNA-miRNA-mRNA network based on circRNA-miRNA interactions and miRNA-mRNA interactions. Protein-protein interactions (PPI) analysis was performed to determine hub genes, and a connectivity map (CMap) analysis was applied to determine potential therapeutic targets for SCI. KEY FINDINGS: A total of 1656 differentially expressed circRNAs (DEcircRNAs), 71 differentially expressed miRNAs (DEmiRNAs) and 2782 differentially expressed mRNAs (DEmRNAs) were identified. We integrated four overlapped circRNAs, six miRNAs and 101 target mRNAs into a circRNA-miRNA-mRNA network. We next identified two hub genes (DDIT4, EZR) based on the PPI network and identified five circRNA-miRNA-hub gene regulatory axes. In addition, we discovered three chemicals (tanespimycin, fulvestrant, carbamazepine) as potential treatment options for SCI. SIGNIFICANCE: Our study suggests a regulatory role for circRNAs in the pathogenesis and treatment of SCI from the view of a competitive endogenous RNA (ceRNA) network.

mRNA decapping is an evolutionarily conserved modulator of neuroendocrine signaling that controls development and ageing.

Eukaryotic 5'-3' mRNA decay plays important roles during development and in response to stress, regulating gene expression post-transcriptionally. In Caenorhabditis elegans, deficiency of DCAP-1/DCP1, the essential co-factor of the major cytoplasmic mRNA decapping enzyme, impacts normal development, stress survival and ageing. Here, we show that overexpression of dcap-1 in neurons of worms is sufficient to increase lifespan through the function of the insulin/IGF-like signaling and its effector DAF-16/FOXO transcription factor. Neuronal DCAP-1 affects basal levels of INS-7, an ageing-related insulin-like peptide, which acts in the intestine to determine lifespan. Short-lived dcap-1 mutants exhibit a neurosecretion-dependent upregulation of intestinal ins-7 transcription, and diminished nuclear localization of DAF-16/FOXO. Moreover, neuronal overexpression of DCP1 in Drosophila melanogaster confers longevity in adults, while neuronal DCP1 deficiency shortens lifespan and affects wing morphogenesis, cell non-autonomously. Our genetic analysis in two model-organisms suggests a critical and conserved function of DCAP-1/DCP1 in developmental events and lifespan modulation.

The new function of circRNA: translation.

Circular RNAs (circRNAs) have been considered a special class of non-coding RNAs without 5' caps and 3' tails which are covalently closed RNA molecules generated by back splicing of mRNA. For a long time, circRNAs have been considered to be directly involved in various biological processes as functional RNA. In recent years, a variety of circRNAs have been found to have translational functions, and the resultant peptides also play biological roles in the emergence and progression of human disease. The discovery of these circRNAs and their encoded peptides has enriched genomics, helped us to study the causes of diseases, and promoted the development of biotechnology. The purpose of this review is to summarize the research progress of the detection methods, translation initiation mechanism, as well as functional mechanism of peptides encoded by circRNAs, with the goal of providing the directions for the discovery of biomarkers for diagnosis, prognosis, and therapeutic targets for human disease.

The m6A epitranscriptome: transcriptome plasticity in brain development and function.

The field of epitranscriptomics examines the recently deciphered form of gene expression regulation that is mediated by type- and site-specific RNA modifications. Similarly to the role played by epigenetic mechanisms - which operate via DNA and histone modifications - epitranscriptomic modifications are involved in the control of the delicate gene expression patterns that are needed for the development and activity of the nervous system and are essential for basic and higher brain functions. Here we describe the mechanisms that are involved in the writing, erasing and reading of N6-methyladenosine, the most prevalent internal mRNA modification, and the emerging roles played by N6-methyladenosine in the nervous system.

Reduction of mRNA export unmasks different tissue sensitivities to low mRNA levels during Caenorhabditis elegans development.

Animal development requires the execution of specific transcriptional programs in different sets of cells to build tissues and functional organs. Transcripts are exported from the nucleus to the cytoplasm where they are translated into proteins that, ultimately, carry out the cellular functions. Here we show that in Caenorhabditis elegans, reduction of mRNA export strongly affects epithelial morphogenesis and germline proliferation while other tissues remain relatively unaffected. Epithelialization and gamete formation demand a large number of transcripts in the cytoplasm for the duration of these processes. In addition, our findings highlight the existence of a regulatory feedback mechanism that activates gene expression in response to low levels of cytoplasmic mRNA. We expand the genetic characterization of nuclear export factor NXF-1 to other members of the mRNA export pathway to model mRNA export and recycling of NXF-1 back to the nucleus. Our model explains how mutations in genes involved in general processes, such as mRNA export, may result in tissue-specific developmental phenotypes.