Long-read sequencing-based atlas of tissue-specific expression of DNM1L transcript variants.

Dynamin-related protein 1 (Drp1), encoded by DNM1L, is essential for mitochondrial fission, but its functional roles remain unclear due to isoform-specific effects from alternative splicing. Short-read RNA sequencing fails to resolve full-length isoforms involving distant exons, limiting our understanding. Here, we applied targeted long-read sequencing to profile full-length DNM1L transcripts in human left ventricle and induced pluripotent stem cell-derived cardiomyocytes, recovering all annotated isoforms with conserved expression patterns and isoforms 1-4 being the most abundant. Functional assays revealed that isoform abundance does not predict enzymatic activity. Extending this to six different mouse tissues, we identified distinct, tissue-enriched expression profiles. Functional rescue in Drp1-knockout mouse embryonic fibroblasts showed isoform-dependent differences in mitochondrial fission. Isoforms lacking the A-insert robustly rescued mitochondrial fission, with maximal activity observed for variants also lacking the B-insert (e.g. isoform b), consistent with a modulatory role of exon 3 in Drp1 activity. Our cross-species atlas integrates long-read transcriptomics with functional validation, revealing how isoform diversity underpins tissue-specific mitochondrial dynamics and physiological roles of Drp1.