Alternative isoforms and phase separation of Ref1 repress morphogenesis in Cryptococcus

Cryptococcus neoformans, the causative agent of cryptococcosis and a representative of the Basidiomycota phylum of Fungi, is a valuable model for our understanding of eukaryotic/fungal biology. Negative feedback is a well-documented mechanism across Eukarya to regulate developmental transitions. Here, we describe a repressor of the yeast-to-hypha transition, Ref1, which completes a negative feedback loop driven by the master regulator of hyphal morphogenesis, Znf2, during sexual development. Alternative transcription of Ref1, driven by Znf2, produces a functionally distinct Ref1 isoform. Isoform-specific capacity for phase separation imparts this functional distinction, making Ref1 a stronger repressor and more vulnerable to proteolytic degradation. The multimodal nature of Ref1 provides versatility that allows cells to fine-tune Ref1 activity to suit developmental context. This work reveals a mechanism by which phase separation allows a transcriptional program to tailor its own repression to guide an organism through morphological transition. [Display omitted] •Cryptococcus morphogenesis activator Znf2 self-regulates via negative feedback by Ref1•Znf2 toggles repressor Ref1 between distinct activity states via alternative transcription•Znf2-induced Ref1 isoform forms condensates, increasing potency and decreasing stability•Ref1 activity is tuned to fit the needs of the developmental state in which it is produced Sexual development is fundamental to the life cycle and evolutionary success of the pathogen Cryptococcus neoformans. Glueck et al. identify negative feedback regulator Ref1 and describe how alternative transcription is employed to alter Ref1’s capacity for phase separation, thus changing Ref1 dynamics to suit the developmental needs of the fungus.