Project description:Alternative mRNA splicing generates transcriptomic diversity to direct tissue-specific functions. There is a high level of alternative splicing in the brain, particularly in development, but the master regulators are poorly understood. A key splicing event early in neuronal differentiation is the inclusion of a microexon in the SH3 domain of the ubiquitous tyrosine kinase, C-SRC, to yield the constitutively active, neural-specific N1-SRC kinase. We previously demonstrated that specific inhibition of N1-SRC in developing Xenopus embryos inhibits neurogenesis, but the targets and mode of action of N1-SRC are unknown. In the current study we screened for N1-SRC SH3 domain interactors, surprisingly finding no unique targets compared to C-SRC, but rather a subset of low affinity binders, enriched in splicing regulators. Analysis of public phosphoproteomic data revealed that SRC-dependent phosphorylation of the splicing machinery is widespread and enriched in RNA binding proteins. To investigate whether N1-SRC-dependent regulation of splicing underpins its role in neurogenesis, we undertook long and short read RNAseq analysis of N1-SRC knockdown Xenopus embryos. We observed an upregulation of splicing factor expression and aberrant splicing of splicing regulators, principally HNRNPA1 and TRA2A. The affected splice junctions in both genes were in their glycine rich C-termini and enriched in SFPQ/NONO and FUS binding sites. These RNA binding proteins are SRC substrates and suggest a mechanism by which N1-SRC knockdown leads to mis-splicing of HNRNPA1 and TRA2A. Thus, the neuronal splicing of C-SRC to generate N1-SRC regulates the alternative splicing landscape during neurogenesis.
Project description:The COVID mRNA vaccines utilize the modified nucleobase N1-methylpseudouridine, in place of canonical uridine, to improve immunogenicity and protein yield. However, relatively few studies have investigated the effect of modified nucleobases on the fidelity of protein translation. Given the interest in the COVID mRNA vaccines, we sought to investigate how N1-methylpseudouridine (and the related modification pseudouridine) is read by ribosomes.
Project description:RNA binding proteins play an important role in regulating alternative pre-mRNA splicing and in turn cellular gene expression. Polypyrimidine tract binding proteins, PTBP1 and PTBP2, are paralogous RNA binding proteins that play a critical role in the process of neuronal differentiation and maturation; changes in the concentration of PTBP proteins during neuronal development direct splicing changes in many transcripts that code for proteins critical for neuronal differentiation. How the two related proteins regulate different sets of neuronal exons is unclear. The distinct splicing activities of PTBP1 and PTBP2 can be recapitulated in an in vitro splicing system with the differentially regulated N1 exon of the c-src pre-mRNA. Here, we conducted experiments under these in vitro splicing conditions to identify PTBP1 and PTBP2 interacting partner proteins.
Project description:We reported that stable expression of constitutively active intra cellular Notch (ICN), in quail neuroretina (QNR) cells transformed by a conditional v-Src mutant (QNR/v-src cells), resulted in the suppression of their transformed properties. Acquisition of a normal phenotype coincided with a major switch in cell identity, as these undifferentiated QNR/v-src cells acquired characteristics of glial differentiation. Similar loss of transformation and gene reprogramming can be achieved in QNR/v-src cells, stably expressing the human CBF protein, RBP-Jk, whose activity was rendered ligand independent by fusion to the VP16 transactivator. These major phenotypic changed are correlated with a dominant interference with signaling effectors, regulating cell morphology and cytoskeleton organization. To understand the mechanisms by which Notch signaling activation suppressed v-Src induced cell transformation and induced differentiation, we compared the transcription profile of QNR cells transformed by a v-Src mutant encoding a temperature sensitive oncoprotein (QNR/v-src), with that of cells stably expressing ICN (QNR/v-src/ICN) or RBP-Jk-VP16 (QNR/v-src/RBP-Jk-VP16). Total RNA was extracted from QNR/v-src, QNR/v-src/ICN or QNR/v-src/RBP-Jk-VP16 cells maintained at permissive (37°C) or restrictive (41°C) temperature. cDNA from QNR/v-src cells was probed with that of QNR/v-src/ICN or QNR/v-src/RBP-Jk-VP16 at both temperature on microarrays spotted with 13,000 cDNA from chicken EST collections designed by the genomic facility of the Fred Hutchinson Cancer Research Center (Seattle). For two sets of sample, dye swap experiments were performed.
Project description:How the ubiquitously expressed splicing factors specifically regulate neural crest (NC) development and enhance their vulnerability to splicing perturbations remain poorly understood. Here, we show that NC-specific DLC1, partnering with SF3B1-PHF5A splicing complex, are crucial for determining avian trunk NC cell fate by regulating the splicing of NC specifiers SOX9 and SNAI2 pre-mRNAs rather than their upstream regulators BMP4, WNT1, and PAX7. Mechanistically, SF3B1-PHF5A binds to the intronic branch site (BS) sequences of all factors, while DLC1 interacts with a specific motif near the BS sequences of SOX9 and SNAI2, thereby determining their functional specificity in NC specification. Moreover, DLC1 increases NC cells’ vulnerability to splicing modulator pladienolide B by reducing the binding capacity of the SF3B1-PHF5A splicing complex to the shorter length of both SOX9 intron 2 and SNAI2 intron 1, which possess weaker polypyrimidine tract 3’ of the BS sequence, resulting in intron retention and loss of NC progenitors. Conversely, somite specific SLU7-SF3B1-PHF5A splicing complex regulates SOX9 and SNAI2 expression and imparts resistance to PB. Our data reveal the cell-type specific splicing complexes with distinct vulnerabilities to PB, highlighting the critical role of the DLC1-SF3B1-PHF5A in determining trunk NC cell fate and enhancing its susceptibility to splicing perturbation.
Project description:We reported that stable expression of constitutively active intra cellular Notch (ICN), in quail neuroretina (QNR) cells transformed by a conditional v-Src mutant (QNR/v-src cells), resulted in the suppression of their transformed properties. Acquisition of a normal phenotype coincided with a major switch in cell identity, as these undifferentiated QNR/v-src cells acquired characteristics of glial differentiation. Similar loss of transformation and gene reprogramming can be achieved in QNR/v-src cells, stably expressing the human CBF protein, RBP-Jk, whose activity was rendered ligand independent by fusion to the VP16 transactivator. These major phenotypic changed are correlated with a dominant interference with signaling effectors, regulating cell morphology and cytoskeleton organization. To understand the mechanisms by which Notch signaling activation suppressed v-Src induced cell transformation and induced differentiation, we compared the transcription profile of QNR cells transformed by a v-Src mutant encoding a temperature sensitive oncoprotein (QNR/v-src), with that of cells stably expressing ICN (QNR/v-src/ICN) or RBP-Jk-VP16 (QNR/v-src/RBP-Jk-VP16).