Abstract
Objective: Alternative splicing (AS) is one of the key mechanisms for the proteomic and functional diversity of eukaryotes. However, the complex nature of AS, its associated regulators and their targets are only partially understood. In the present study we investigated the transcriptomic diversity in the zebrafish heart using RNA-Sequencing and elucidated the functional role of the splicing regulator A2BP1 in vivo. Results: Using RNA-Sequencing we characterized the cardiac transcriptome of 48 hours post fertilization (hpf) old zebrafish embryos and compared the expression of genes and their isoforms to whole fish tissue. Besides the known cardiac genes, we found several previously described genes, highly expressed in cardiac tissue. The analysis of RNA-Seq data indicates that 14% of all genes expressed in the heart undergo AS by single exon-skipping/inclusion. To determine the effect of splicing factors on mRNA splicing we investigated the functional role of splicing regulator a2bp1 in vivo by using the zebrafish as a model organism. Morpholino-mediated a2bp1 knockdown in zebrafish embryos led to progressive cardiac contractile dysfunction, suggesting an important role of a2bp1 in maintenance of cardiac function. Splicing analysis revealed that loss of a2bp1 does not result in a completely splicing failure, but rather alters the splicing pattern of specific target genes. Here we identified novel spliceforms and potentialy novel targets of splicing factor a2bp1. Splice-junction blockage experiments showed that a balanced isoform expression of the targets actn3a, hug, ktn1, ptpla and camk2g is necessary for maintaining cardiac function in zebrafish. We assume, that the a2bp1-knockdown phenotype is not caused by missplicing of specific targets rather by the cumulative effect of many splicing abnormalities. Conclusion: Our study reveal a novel splicing regulator that is necessary for normal heart function. We showed that dysfunction of a2bp1 not only leads to heart failure, but show that a2bp1 mediates the splicing of different transcripts which might mediate the observed phenotype. Our results highlight the importance of balanced mRNA splicing in the heart and represents intriguing opportunities for novel therapeutic approaches.
Published Version
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