UCSF

Multicellular development in the choanoflagellate Salpingoeca rosetta is regulated by environmental cues, providing a model for understanding how external signals influence developmental programs in the closest living relatives of animals. In this dissertation, I identify the red algal polysaccharide porphyran as a potent inducer of multicellular development and use it as a tool to investigate the molecular mechanisms underlying this process. Transcriptomic and proteomic analyses revealed an enrichment of genes and proteins associated with carbohydrate recognition and vesicular trafficking in response to porphyran. A combination of proteomics and CRISPR-Cas9 genome editing identified soltero, a gene encoding previously uncharacterized RicinB-domain-containing protein, as a necessary component of multicellular development in response to both porphyran and bacterial lipids. Loss of soltero disrupts extracellular matrix organization and prevents secretion of the necessary developmental protein Rosetteless, demonstrating a critical role for extracellular matrix assembly in rosette development. Together, these findings uncover a connection between environmental carbohydrate sensing, secretory remodeling, and multicellular development, providing new insight into mechanisms that may have contributed to the evolution of animal multicellularity.