Christopher B. Burge | bioRxiv Science

bioRxiv2014

Functional Antagonism Between CELF and Mbnl Proteins in the Cytoplasm

The conserved CUGBP1, Elav-like (CELF) family of RNA binding proteins contribute to heart and skeletal muscle development and are implicated in myotonic dystrophy (DM). To understand genome-wide functions of CELF proteins, we analyzed transcriptome dynamics following induction of CELF1 or CELF2 in adult mouse heart or CELF1 in muscle by RNA-seq, complemented by crosslinking/immunoprecipitation-sequencing (CLIP-seq) analysis of mouse cells and tissues to distinguish direct from indirect regulatory targets. Analysis of expression and mRNA binding data revealed hundreds of mRNAs bound in their 3' UTRs by both CELF1 and and the developmentally induced Mbnl1 protein, 3-fold more than expected. The relative extent of CELF1 and Mbnl1 binding in 3' UTRs predicted the extent of repression or stabilization, respectively, following CELF induction. These findings support a ?Cytoplasmic Competition? model in which CELF and Mbnl proteins compete to specify degradation or membrane localization/stabilization, respectively, of an overlapping set of targets. Several hundred messages contained proximal CELF1 and Mbnl1 binding sites (within 50 bases), and were more strongly repressed by CELF1 than messages with distal sites. Messages with different spacing of CELF and Mbnl sites in their 3' UTRs exhibited different developmental dynamics, suggesting that spacing is used to tune cytoplasmic competition between these factors to specify the timing of developmental induction. CELF1 also shared dozens of splicing targets with Mbnl1, most regulated oppositely, confirming a phenomenon observed in smaller scale studies but not previously supported by genome-wide methods, which also appears to enhance developmental transitions.

Genomics↗

bioRxiv2014

Rapid transcriptional response to physiological neuronal activity in vivo revealed by transcriptome sequencing

Neuronal activity serves as a gateway between external stimulus from environment and the brain, often inducing gene expression changes. Alternative splicing (AS) is a widespread mechanism of increasing the number of transcripts produced from a single gene and has been shown to alter properties of neuronal genes, such as ion channels (Xie and Black 2001) and neurotransmitter receptors (Mu et al. 2003). Patterns of neural tissue-specific AS have been identified, often regulated by neuron-specific splicing factors that are essential for survival (Jensen et al. 2000; Li et al. 2007), demonstrating the importance of AS in neurons. In vitro studies of neuronal activity found AS changes in response to neuronal activity in addition to transcriptional ones, raising the question of whether such changes are recapitulated in vivo on behaviorally relevant timescales. We developed a paradigm for studying physiological neuronal activity through controlled stimulation of the olfactory bulb, and performed RNA-Seq transcriptome analysis of olfactory bulbs from odor-deprived and stimulated mice. We found that physiological stimulation induces large, rapid and reproducible changes in transcription in vivo, and that the activation of a core set of activity-regulated factors is recapitulated in an in vitro model of neuronal stimulation. However, physiological activity did not induce global changes in post-transcriptional mRNA processing, such as AS or alternative cleavage and polyadenylation. In contrast, analysis of RNA-Seq from in vitro stimulation models showed rapid activity-dependent changes in both transcription and mRNA processing. Our results provide the first genome-wide look at neuronal activity-dependent mRNA processing and suggest that rapid changes in AS might not be the dominant form of transcriptome alterations that take place during olfactory rodent behavior.

Neuroscience↗