Metazoan development depends on accurate execution of differentiation programs that allow pluripotent stem cells to adopt specific fates 1. Differentiation requires changes to chromatin architecture and transcriptional networks, yet whether other regulatory events support cell fate determination is less well understood. Here, we have identified the vertebrate-specific ubiquitin ligase CUL3KBTBD8 as an essential regulator of neural crest specification. CUL3KBTBD8 monoubiquitylates NOLC1 and its paralog TCOF1, whose mutation underlies the neurocristopathy Treacher Collins Syndrome 2,3. Ubiquitylation drives formation of a TCOF1-NOLC1 platform that connects RNA polymerase I with ribosome modification enzymes and remodels the translational program of differentiating cells in favor of neural crest specification. We conclude that ubiquitin-dependent regulation of translation is an important feature of cell fate determination.

The ubiquitin ligase CUL3 is an essential regulator of neural crest specification whose aberrant activation has been linked to autism, schizophrenia, and hypertension. CUL3 exerts its roles by pairing with ∼90 distinct substrate adaptors, yet how the different CUL3-complexes are activated is poorly understood. Here, we show that CUL3 and its adaptor KLHL12 require two calcium-binding proteins, PEF1 and ALG2, for recognition of their substrate SEC31. PEF1 and ALG2 form a target-specific co-adaptor that translates a transient rise in cytosolic calcium levels into more persistent SEC31 ubiquitylation, which in turn triggers formation of large COPII coats and promotes collagen secretion. As calcium also instructs chondrocyte differentiation and collagen synthesis, calcium-dependent control of CUL3 integrates collagen secretion into broader programs of craniofacial bone formation. Our work, therefore, identifies both calcium and CUL3 co-adaptors as important regulators of ubiquitylation events that control human development.

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To ensure proper attachment of all chromosomes to the spindle, PLK1 has to associate with kinetochores during prometaphase and must be released from these sites before sister chromatid separation can begin. The monoubiquitylation of PLK1 by the ubiquitin ligase CUL3-KLHL22 is now identified as a critical step in promoting the release of PLK1 from kinetochores, pushing non-proteolytic ubiquitylation into the limelight of cell division research.