Epigenetic control of adaptive or homeostatic splicing during interval-training activities.

Interval-training activities induce adaptive cellular changes without altering their fundamental identity, but the precise underlying molecular mechanisms are not fully understood. In this study, we demonstrate that interval-training depolarization (ITD) of pituitary cells triggers distinct adaptive or homeostatic splicing responses of alternative exons. This occurs while preserving the steady-state expression of the Prolactin and other hormone genes. The nature of these splicing responses depends on the exon's DNA methylation status, the methyl-C-binding protein MeCP2 and its associated CA-rich motif-binding hnRNP L. Interestingly, the steady expression of the Prolactin gene is also reliant on MeCP2, whose disruption leads to exacerbated multi-exon aberrant splicing and overexpression of the hormone gene transcripts upon ITD, similar to the observed hyperprolactinemia or activity-dependent aberrant splicing in Rett Syndrome. Therefore, epigenetic control is crucial for both adaptive and homeostatic splicing and particularly the steady expression of the Prolactin hormone gene during ITD. Disruption in this regulation may have significant implications for the development of progressive diseases.

Transcriptome-Wide Detection of Intron/Exon Definition in the Endogenous Pre-mRNA Transcripts of Mammalian Cells and Its Regulation by Depolarization.

Pairing of splice sites across an intron or exon is the central point of intron or exon definition in pre-mRNA splicing with the latter mode proposed for most mammalian exons. However, transcriptome-wide pairing within endogenous transcripts has not been examined for the prevalence of each mode in mammalian cells. Here we report such pairings in rat GH3 pituitary cells by measuring the relative abundance of nuclear RNA-Seq reads at the intron start or end (RISE). Interestingly, RISE indexes are positively correlated between 5' and 3' splice sites specifically across introns or exons but inversely correlated with the usage of adjacent exons. Moreover, the ratios between the paired indexes were globally modulated by depolarization, which was disruptible by 5-aza-Cytidine. The nucleotide matrices of the RISE-positive splice sites deviate significantly from the rat consensus, and short introns or exons are enriched with the cross-intron or -exon RISE pairs, respectively. Functionally, the RISE-positive genes cluster for basic cellular processes including RNA binding/splicing, or more specifically, hormone production if regulated by depolarization. Together, the RISE analysis identified the transcriptome-wide regulation of either intron or exon definition between weak splice sites of short introns/exons in mammalian cells. The analysis also provides a way to further track the splicing intermediates and intron/exon definition during the dynamic regulation of alternative splicing by extracellular factors.

Genome-wide evolution of wobble base-pairing nucleotides of branchpoint motifs with increasing organismal complexity.

How have the branchpoint motifs evolved in organisms of different complexity? Here we identified and examined the consensus motifs (R1C2T3R4A5Y6, R: A or G, Y: C or T) of 898 fungal genomes. In Ascomycota unicellular yeasts, the G4/A4 ratio is mostly (98%) below 0.125 but increases sharply in multicellular species by about 40 times on average, and in the more complex Basidiomycota, it increases further by about 7 times. The global G4 increase is consistent with A4 to G4 transitions in evolution. Of the G4/A4-interacting amino acids of the branchpoint binding protein MSL5 (SF1) and the HSH155 (SF3B1), as well as the 5' splice sites (SS) and U2 snRNA genes, the 5' SS G3/A3 co-vary with the G4 to some extent. However, corresponding increase of the G4-complementary GCAGTA-U2 gene is rare, suggesting wobble-base pairing between the G4-containing branchpoint motif and GTAGTA-U2 in most of these species. Interestingly, the G4/A4 ratio correlates well with the abundance of alternative splicing in the two phyla, and G4 enriched significantly at the alternative 3' SS of genes in RNA metabolism, kinases and membrane proteins. Similar wobble nucleotides also enriched at the 3' SS of multicellular fungi with only thousands of protein-coding genes. Thus, branchpoint motifs have evolved U2-complementarity in unicellular Ascomycota yeasts, but have gradually gained more wobble base-pairing nucleotides in fungi of higher complexity, likely to destabilize branchpoint motif-U2 interaction and/or branchpoint A protrusion for alternative splicing. This implies an important role of relaxing the branchpoint signals in the multicellularity and further complexity of fungi.

Transcriptome protection by the expanded family of hnRNPs.

The family of heterogeneous ribonucleoproteins (hnRNPs) have multiple functions in RNA metabolism. In recent years, several hnRNPs have also been shown to be essential for the maintenance of transcriptome integrity, by preventing intronic cryptic splicing signals from mis-splicing of many endogeneous pre-mRNA transcripts. Here we discuss the possibility for a general role of this family of proteins and their expansion in transcriptome protection.

Increase of a group of PTC(+) transcripts by curcumin through inhibition of the NMD pathway.

Nonsense-mediated mRNA decay (NMD), an mRNA surveillance mechanism, eliminates premature termination codon-containing (PTC⁺) transcripts. For instance, it maintains the homeostasis of splicing factors and degrades aberrant transcripts of human genetic disease genes. Here we examine the inhibitory effect on the NMD pathway and consequent increase of PTC+ transcripts by the dietary compound curcumin. We have found that several PTC⁺ transcripts including that of serine/arginine-rich splicing factor 1 (SRSF1) were specifically increased in cells by curcumin. We also observed a similar curcumin effect on the PTC⁺ mutant transcript from a Tay-Sachs-causing HEXA allele or from a beta-globin reporter gene. The curcumin effect was accompanied by significantly reduced expression of the NMD factors UPF1, 2, 3A and 3B. Consistently, in chromatin immunoprecipitation assays, curcumin specifically reduced the occupancy of acetyl-histone H3 and RNA polymerase II at the promoter region (-376 to -247nt) of human UPF1, in a time- and dosage-dependent way. Importantly, knocking down UPF1 abolished or substantially reduced the difference of PTC(+) transcript levels between control and curcumin-treated cells. The disrupted curcumin effect was efficiently rescued by expression of exogenous Myc-UPF1 in the knockdown cells. Together, our data demonstrate that a group of PTC⁺ transcripts are stabilized by a dietary compound curcumin through the inhibition of UPF factor expression and the NMD pathway.

Differential expression, distinct localization and opposite effect on Golgi structure and cell differentiation by a novel splice variant of human PRMT5.

Alternative splicing contributes greatly to the proteomic diversity of metazoans. Protein arginine methyltransferase 5 (PRMT5) methylates arginines of Golgi components and other factors exerting diverse effects on cell growth/differentiation, but the underlying molecular basis for its subcellular distribution and diverse roles has not been fully understood. Here we show the detailed properties of an evolutionarily emerged splice variant of human PRMT5 (PRMT5S) that is distinct from the original isoform (PRMT5L). The isoforms are differentially expressed among mammalian cells and tissues. The PRMT5S is distributed all over the cell but PRMT5L mainly colocalizes with Giantin, a Golgi marker. PRMT5 knockdown led to an enlarged Giantin pattern, which was prevented by the expression of either isoform. Rescuing PRMT5S also increased the percentage of cells with an interphase Giantin pattern compacted at one end of the nucleus, consistent with its cell cycle-arresting effect, while rescuing PRMT5L increased that of the mitotic Giantin patterns of dynamically fragmented structures. Moreover, the isoforms are differentially expressed during neuronal or dendritic cell differentiation, and their ectopic expression showed an opposite effect on dendritic cell differentiation. Furthermore, besides their differential regulation of gene expression, both isoforms also similarly regulate over a thousand genes particularly those involved in apoptosis and differentiation. Taking these properties together, we propose that their differential expression and subcellular localization contribute to spatial and temporal regulation of arginine methylation and gene expression to exert different effects. The novel PRMT5S likely contributes to the observed diverse effects of PRMT5 in cells.

Increased stability of heterogeneous ribonucleoproteins by a deacetylase inhibitor.

Splicing factors are often influenced by various signaling pathways, contributing to the dynamic changes of protein isoforms in cells. Heterogeneous ribonucleoproteins (hnRNPs) regulate many steps of RNA metabolism including pre-mRNA splicing but their control by cell signaling particularly through acetylation and ubiquitination pathways remains largely unknown. Here we show that TSA, a deacetylase inhibitor, reduced the ratio of Bcl-x splice variants Bcl-xL/xS in MDA-MB-231 breast cancer cells. This TSA effect was independent of TGFß1; however, only in the presence of TGFß1 was TSA able to change the splicing regulators hnRNP F/H by slightly reducing their mRNA transcripts but strongly preventing protein degradation. The latter was also efficiently prevented by lactacystin, a proteasome inhibitor, suggesting their protein stability control by both acetylation and ubiquitination pathways. Three lysines K87, K98 and K224 of hnRNP F are potential targets of the mutually exclusive acetylation or ubiquitination (K(Ac/Ub)) in the protein modification database PhosphoSitePlus. Mutating each of them but not a control non-K(Ac/Ub) (K68) specifically abolished the TSA enhancement of protein stability. Moreover, mutating K98 (K98R) and K224 (K224R) also abolished the TSA regulation of alternative splicing of a Bcl-x mini-gene. Furthermore, about 86% (30 of 35) of the multi-functional hnRNP proteins in the database contain lysines that are potential sites for acetylation/ubiquitination. We demonstrate that the degradation of three of them (A1, I and L) are also prevented by TSA. Thus, the deacetylase inhibitor TSA enhances hnRNP F stability through the K(Ac/Ub) lysines, with some of them essential for its regulation of alternative splicing. Such a regulation of protein stability is perhaps common for a group of hnRNPs and RNA metabolism.

Diverse regulation of 3' splice site usage.

The regulation of splice site (SS) usage is important for alternative pre-mRNA splicing and thus proper expression of protein isoforms in cells; its disruption causes diseases. In recent years, an increasing number of novel regulatory elements have been found within or nearby the 3'SS in mammalian genes. The diverse elements recruit a repertoire of trans-acting factors or form secondary structures to regulate 3'SS usage, mostly at the early steps of spliceosome assembly. Their mechanisms of action mainly include: (1) competition between the factors for RNA elements, (2) steric hindrance between the factors, (3) direct interaction between the factors, (4) competition between two splice sites, or (5) local RNA secondary structures or longer range loops, according to the mode of protein/RNA interactions. Beyond the 3'SS, chromatin remodeling/transcription, posttranslational modifications of trans-acting factors and upstream signaling provide further layers of regulation. Evolutionarily, some of the 3'SS elements seem to have emerged in mammalian ancestors. Moreover, other possibilities of regulation such as that by non-coding RNA remain to be explored. It is thus likely that there are more diverse elements/factors and mechanisms that influence the choice of an intron end. The diverse regulation likely contributes to a more complex but refined transcriptome and proteome in mammals.

Refinement of the spectra of exon usage by combined effects of extracellular stimulus and intracellular factors.

Finely tuned differential expression of alternative splice variants contributes to important physiological processes such as the fine-tuning of electrical firing or hearing frequencies; yet the underlying molecular basis for the expression control is not clear. The inclusion levels of four depolarization-regulated alternative exons were measured by RT-PCR in GH3 pituitary cells under different conditions of stimulation and/or RNA interference of splicing factors. The usage of the exons was reduced by membrane depolarization to various extents and was differentially modulated by the knock-down of splicing factors hnRNP L, L-like, I (PTBP1) or K or their combinations. A spectrum of each exon's level was produced under six knock-down conditions and was significantly shifted by depolarization. When all these conditions were considered together, a more refined or expanded spectrum of exon usage was obtained for each of the four exons. As a proof of principle for the molecular basis of the fine-tuning of exon usage, we show in the cases of hnRNP L and LL that their differential effects through the same element or different combinations of RNA sequences by the same factor hnRNP L are critical. The results thus demonstrate that the combined effect of varying extracellular stimuli and intracellular factors/RNA sequences refines or expands the spectra of endogenous exon usage, likely contributing to the fine-tuning of cellular properties.

Differential evolution of signal-responsive RNA elements and upstream factors that control alternative splicing.

Cell signal-regulated alternative splicing occurs for many genes but the evolutionary origin of the regulatory components and their relationship remain unclear. This review focuses on the alternative splicing components of several systems based on the available bioinformatics data. Eight mammalian RNA elements for signal-regulated splicing were aligned among corresponding sequences from dozens of representative vertebrate species to allow for assessment of the trends in evolutionary changes. Four distinct trends were observed. Four of the elements are highly conserved in bird, reptile and fish species examined (i); two elements can be found in fish but the sequences have been changing till in marsupials or higher mammals (ii); one element is almost exclusively found in mammals with mostly the same sequence (iii); and one element can be found in birds or lower vertebrates but expanded abruptly to have variable numbers of copies in mammals (iv). All examined prototype trans-acting factors and protein kinases emerged earlier than the RNA elements but additional (paralog) factors emerged in the same or later species. Thus, after their emergence mainly in fish or mammals with pre-existing prototype trans-acting factors/kinases, half of the elements have been highly conserved from fish to humans but the other half have evolved differentially with additional trans-acting factors. Their differential evolution likely contributes to the exon- and species/class-specific control of alternative splicing and its regulation by cell signals. The evolvement of a group of mammal-specific components would help relay signals from extracellular stimuli to the splicing machinery and thus contribute to higher proteomic diversity.

Evolutionarily emerged G tracts between the polypyrimidine tract and 3' AG are splicing silencers enriched in genes involved in cancer.

BACKGROUND: The 3' splice site (SS) at the end of pre-mRNA introns has a consensus sequence (Y)nNYAG for constitutive splicing of mammalian genes. Deviation from this consensus could change or interrupt the usage of the splice site leading to alternative or aberrant splicing, which could affect normal cell function or even the development of diseases. We have shown that the position "N" can be replaced by a CA-rich RNA element called CaRRE1 to regulate the alternative splicing of a group of genes. RESULTS: Taking it a step further, we searched the human genome for purine-rich elements between the -3 and -10 positions of the 3' splice sites of annotated introns. This identified several thousand such 3'SS; more than a thousand of them contain at least one copy of G tract. These sites deviate significantly from the consensus of constitutive splice sites and are highly associated with alterative splicing events, particularly alternative 3' splice and intron retention. We show by mutagenesis analysis and RNA interference that the G tracts are splicing silencers and a group of the associated exons are controlled by the G tract binding proteins hnRNP H/F. Species comparison of a group of the 3'SS among vertebrates suggests that most (~87%) of the G tracts emerged in ancestors of mammals during evolution. Moreover, the host genes are most significantly associated with cancer. CONCLUSION: We call these elements together with CaRRE1 regulatory RNA elements between the Py and 3'AG (REPA). The emergence of REPA in this highly constrained region indicates that this location has been remarkably permissive for the emergence of de novo regulatory RNA elements, even purine-rich motifs, in a large group of mammalian genes during evolution. This evolutionary change controls alternative splicing, likely to diversify proteomes for particular cellular functions.

Emerging mechanisms and consequences of calcium regulation of alternative splicing in neurons and endocrine cells.

Alternative splicing contributes greatly to proteomic complexity. How it is regulated by external stimuli to sculpt cellular properties, particularly the highly diverse and malleable neuronal properties, is an underdeveloped area of emerging interest. A number of recent studies in neurons and endocrine cells have begun to shed light on its regulation by calcium signals. Some mechanisms include changes in the trans-acting splicing factors by phosphorylation, protein level, alternative pre-mRNA splicing, and nucleocytoplasmic redistribution of proteins to alter protein-RNA or protein-protein interactions, as well as modulation of chromatin states. Importantly, functional analyses of the control of specific exons/splicing factors in the brain point to a crucial role of this regulation in synaptic maturation, maintenance, and transmission. Furthermore, its deregulation has been implicated in the pathogenesis of neurological disorders, particularly epilepsy/seizure. Together, these studies have not only provided mechanistic insights into the regulation of alternative splicing by calcium signaling but also demonstrated its impact on neuron differentiation, function, and disease. This may also help our understanding of similar regulations in other types of cells.

Control of alternative splicing by forskolin through hnRNP K during neuronal differentiation.

The molecular basis of cell signal-regulated alternative splicing at the 3' splice site remains largely unknown. We isolated a protein kinase A-responsive ribonucleic acid (RNA) element from a 3' splice site of the synaptosomal-associated protein 25 (Snap25) gene for forskolin-inhibited splicing during neuronal differentiation of rat pheochromocytoma PC12 cells. The element binds specifically to heterogeneous nuclear ribonucleo protein (hnRNP) K in a phosphatase-sensitive way, which directly competes with the U2 auxiliary factor U2AF65, an essential component of early spliceosomes. Transcripts with similarly localized hnRNP K target motifs upstream of alternative exons are enriched in genes often associated with neurological diseases. We show that such motifs upstream of the Runx1 exon 6 also bind hnRNP K, and importantly, hnRNP K is required for forskolin-induced repression of the exon. Interestingly, this exon encodes the peptide domain that determines the switch of the transcriptional repressor/activator activity of Runx1, a change known to be critical in specifying neuron lineages. Consistent with an important role of the target genes in neurons, knocking down hnRNP K severely disrupts forskolin-induced neurite growth. Thus, through hnRNP K, the neuronal differentiation stimulus forskolin targets a critical 3' splice site component of the splicing machinery to control alternative splicing of crucial genes. This also provides a regulated direct competitor of U2AF65 for cell signal control of 3' splice site usage.

A conserved serine of heterogeneous nuclear ribonucleoprotein L (hnRNP L) mediates depolarization-regulated alternative splicing of potassium channels.

Molecular mechanisms of gene regulation underlying the activity-dependent long term changes of cellular electrical properties, such as those during memory, are largely unknown. We have shown that alternative splicing can be dynamically regulated in response to membrane depolarization and Ca(2+)/calmodulin-dependent protein kinase IV (CaMKIV) activation, through special CaM kinase responsive RNA elements. However, proteins that mediate this regulation and how they are affected by CaMKIV are not known. Here we show that the regulation of the stress axis-regulated exon of the Slo1 potassium channel transcripts by membrane depolarization requires a highly conserved CaMKIV target serine (Ser-513) of the heterogeneous ribonucleoprotein L. Ser-513 phosphorylation within the RNA recognition motif 4 enhanced heterogeneous ribonucleoprotein L interaction with the CaMKIV-responsive RNA element 1 of stress axis-regulated exon and inhibited binding of the large subunit of the U2 auxiliary factor U2AF65. Both of these activities were abolished by a S513A mutation. Thus, through Ser-513, membrane depolarization/calcium signaling controls a critical spliceosomal assembly step to regulate the variant subunit composition of potassium channels.

Variations of intronic branchpoint motif: identification and functional implications in splicing and disease.

The branchpoint (BP) motif is an essential intronic element for spliceosomal pre-mRNA splicing. In mammals, its sequence composition, distance to the downstream exon, and number of BPs per 3´ splice site are highly variable, unlike the GT/AG dinucleotides at the intron ends. These variations appear to provide evolutionary advantages for fostering alternative splicing, satisfying more diverse cellular contexts, and promoting resilience to genetic changes, thus contributing to an extra layer of complexity for gene regulation. Importantly, variants in the BP motif itself or in genes encoding BP-interacting factors cause human genetic diseases or cancers, highlighting the critical function of BP motif and the need to precisely identify functional BPs for faithful interpretation of their roles in splicing. In this perspective, we will succinctly summarize the major findings related to BP motif variations, discuss the relevant issues/challenges, and provide our insights.

Forming cytoplasmic stress granules PURα suppresses mRNA translation initiation of IGFBP3 to promote esophageal squamous cell carcinoma progression.

Esophageal squamous cell carcinoma (ESCC) is one of the most fatal malignancies worldwide. Recently, our group identified purine-rich element binding protein alpha (PURα), a single-stranded DNA/RNA-binding protein, to be significantly associated with the progression of ESCC. Additional immunofluorescence staining demonstrated that PURα forms cytoplasmic stress granules to suppress mRNA translation initiation. The expression level of cytoplasmic PURα in ESCC tumor tissues was significantly higher than that in adjacent epithelia and correlated with a worse patient survival rate by immunohistochemistry. Functionally, PURα strongly preferred to bind to UG-/U-rich motifs and mRNA 3´UTR by CLIP-seq analysis. Moreover, PURα knockout significantly increased the protein level of insulin-like growth factor binding protein 3 (IGFBP3). In addition, it was further demonstrated that PURα-interacting proteins are remarkably associated with translation initiation factors and ribosome-related proteins and that PURα regulates protein expression by interacting with translation initiation factors, such as PABPC1, eIF3B and eIF3F, in an RNA-independent manner, while the interaction with ribosome-related proteins is significantly dependent on RNA. Specifically, PURα was shown to interact with the mRNA 3´UTR of IGFBP3 and inhibit its expression by suppressing mRNA translation initiation. Together, this study identifies cytoplasmic PURα as a modulator of IGFBP3, which could be a promising therapeutic target for ESCC treatment.

Differential effects of PKA-controlled CaMKK2 variants on neuronal differentiation.

Regulation between protein kinases is critical for the establishment of signaling pathways/networks to 'orchestrate' cellular processes. Besides posttranslational phosphorylation, alternative pre-mRNA splicing is another way to control kinase properties, but splicing regulation between two kinases and the effect of resulting variants on cells has barely been explored. Here we examined the effect of the protein kinase A (PKA) pathway on the alternative splicing and variant properties of the Ca²âº/calmodulin-dependent protein kinase kinase 2 (CaMKK2) gene in B35 neuroblastoma cells. Inclusion of the exon 16 of CaMKK2 was significantly reduced by H89, a PKA selective inhibitor. Consistently, overexpressed PKA strongly promoted the exon inclusion in a CaMKK2 sequence-dependent way in splicing reporter assays. In vitro, purified CaMKKß1 variant proteins were found to be kinase-active. In cells, they were differentially phosphorylated by PKA. In RNA interference assays, CaMKKß1 was found to be essential for forskolin-induced neurite growth. Interestingly, overexpression of the variant without exon 16 (-E16) promoted neurite elongation while the other one (+E16) promoted neurite branching; in contrast, reduction of the latter one enhanced neurite elongation. Moreover, the variants are differentially expressed and the exon 16-containing transcripts highly enriched in the brain, particularly the cerebellum and hippocampus. Thus, PKA regulates the alternative splicing of CaMKK2 to produce variants that differentially modulate neuronal differentiation. Taken together with the many distinct variants of kinases, alternative splicing regulation likely adds another layer of modulation between protein kinases in cellular signaling networks.

Depolarization and CaM kinase IV modulate NMDA receptor splicing through two essential RNA elements.

Alternative splicing controls the activity of many proteins important for neuronal excitation, but the signal-transduction pathways that affect spliced isoform expression are not well understood. One particularly interesting system of alternative splicing is exon 21 (E21) of the NMDA receptor 1 (NMDAR1 E21), which controls the trafficking of NMDA receptors to the plasma membrane and is repressed by Ca(++)/calmodulin-dependent protein kinase (CaMK) IV signaling. Here, we characterize the splicing of NMDAR1 E21. We find that E21 splicing is reversibly repressed by neuronal depolarization, and we identify two RNA elements within the exon that function together to mediate the inducible repression. One of these exonic elements is similar to an intronic CaMK IV-responsive RNA element (CaRRE) originally identified in the 3' splice site of the BK channel STREX exon, but not previously observed within an exon. The other element is a new RNA motif. Introduction of either of these two motifs, called CaRRE type 1 and CaRRE type 2, into a heterologous constitutive exon can confer CaMK IV-dependent repression on the new exon. Thus, either exonic CaRRE can be sufficient for CaMK IV-induced repression. Single nucleotide scanning mutagenesis defined consensus sequences for these two CaRRE motifs. A genome-wide motif search and subsequent RT-PCR validation identified a group of depolarization-regulated alternative exons carrying CaRRE consensus sequences. Many of these exons are likely to alter neuronal function. Thus, these two RNA elements define a group of co-regulated splicing events that respond to a common stimulus in neurons to alter their activity.

A G-tract element in apoptotic agents-induced alternative splicing.

Alternative splicing of a single pre-mRNA transcript can produce protein isoforms that promote either cell growth or death. Here we show that Ro-31-8220 (Ro), an apoptotic agent that inhibits protein kinase C and activates the c-Jun N terminal kinase, decreased the proportion of the cell growth-promoting Bcl-xL splice variant. Targeted mutagenesis analyses narrowed down a critical sequence to a 16-nt G-tract element (Gt16). Transferring this element to a heterologous gene conferred Ro response on an otherwise constitutive exon. The Ro effect was reduced by okadaic acid, an inhibitor of protein phosphatases PP1 and PP2A, in a concentration-dependent manner. Search in the human genome followed by RT-PCR identified a group of genes that contain similar exonic G-tract elements and are responsive to Ro. Moreover, the Gt16 element also mediates the regulation of alternative splicing by other cell apoptosis-inducers particularly retinoic acid. Therefore, the G-tract element likely plays a role in the apoptotic agents-induced alternative splicing of a group of genes. The functions of these genes imply that this regulation will have impact on cell growth/death.

Control of alternative pre-mRNA splicing by Ca(++) signals.

Alternative pre-mRNA splicing is a common way of gene expression regulation in metazoans. The selective use of specific exons can be modulated in response to various manipulations that alter Ca(++) signals, particularly in neurons. A number of splicing factors have also been found to be controlled by Ca(++) signals. Moreover, pre-mRNA elements have been identified that are essential and sufficient to mediate Ca(++)-regulated splicing, providing model systems for dissecting the involved molecular components. In neurons, this regulation likely contributes to the fine-tuning of neuronal properties.