Cell Type-specific Isoform Function Prediction by Multiplex Heterogeneous Network.

Alternatively spliced isoforms from the same gene can perform distinct functions; however, their cell-type-specific roles remain largely uncharacterized, limiting our ability to understand cellular diversity and development beyond traditional gene-level analyses. We present cIsoFun, a multi-modal fusion framework for cell-type-specific isoform function prediction from single-cell transcriptomics data. cIsoFun leverages pre-trained ESM-2 and BERT models to extract initial sequence features, constructs a multiplex heterogeneous network over genes, isoforms, GO terms, and cell types to represent their complex relationships, and applies relation-aware attention to integrate multi-modal information and refine node embeddings. It then optimizes a multi-component loss on the updated embeddings to predict isoform functions, enabling biological interpretability via sequence-importance and cell-type-specific analyses. Experiments demonstrate that cIsoFun outperforms existing methods, particularly for sparse GO terms, and reveal distinct functional programs across contexts: kidney tumor cells are enriched for metabolism and growth regulation, skin tumor cells emphasize immune surveillance and migration, and cell lines prioritize DNA repair and telomere maintenance. Sequence-importance analysis highlights critical amino-acid regions and shows that domains annotated with the same function can exhibit distinct importance profiles across spliced isoforms. Together, these results provide new insights into cell-type-specific isoform functionality and establish cIsoFun as a practical tool for single-cell isoform analysis. Code and datasets are available at www.sdu-idea.cn/codes.php?name=cIsoFun.