The dynamic landscape of fission yeast meiosis alternative-splice isoforms

Abstract

Alternative splicing increases the diversity of transcriptomes and proteomes in metazoans. The extent to which alternative splicing is active and functional in unicellular organisms is less understood. Here we exploit a single-molecule long-read sequencing technique and develop an open-source software program called SpliceHunter to characterize the transcriptome in the meiosis of fission yeast. We reveal 14353 alternative splicing events in 17669 novel isoforms at different stages of meiosis, including antisense and read-through transcripts. Intron retention is the major type of alternative splicing, followed by alternate 'intron in exon'. 770 novel transcription units are detected; 53 of the predicted proteins show homology in other species and form theoretical stable structures. We report the complexity of alternative splicing along isoforms, including 683 intramolecularly co-associated intron pairs. We compare the dynamics of novel isoforms based on the number of supporting full-length reads with those of annotated isoforms and explore the translational capacity and quality of novel isoforms. The evaluation of these factors indicates that the majority of novel isoforms are unlikely to be both condition-specific and translatable but consistent with the possibility of biologically functional novel isoforms. Moreover, the co-option of these unusual transcripts into newly born genes seems likely. Together, this study highlights the diversity and dynamics at the isoform level in the sexual development of fission yeast.