Cell fate determination by ubiquitin-dependent regulation of ribosome function

Metazoan development depends on accurate execution of differentiation programs that allow pluripotent stem cells to adopt specific fates. Differentiation is brought about by global changes to chromatin architecture and transcriptional networks, yet whether other regulatory events support cell fate determination is less well understood. Using a human embryonic stem cell model, we identified the vertebrate-specific ubiquitin ligase Cul3KBTBD8 as an essential regulator of neural crest cell formation. Cul3KBTBD8 monoubiquitylates NOLC1 and its paralog TCOF1, whose mutation underlies the developmental disease Treacher Collins Syndrome that is characterized by a loss of cranial neural crest cells. Ubiquitylation of NOLC1 and TCOF1 drives formation of a platform that connects RNA polymerase I with ribosome modification enzymes, thereby altering the translational program of differentiating cells to support the generation of neural crest cells. We conclude that the dynamic regulation of ribosome function is an important feature of cell fate determination. Affymetrix assays were performed according to the manufacturer's directions on total RNA isolated from three independent samples of human embryonic stem cells (hESC) H1 cells or cells that had been differentiated into embryoid bodies for 6 days. Where indicated, hESC cells were transduced with control shRNA or shRNA targeting KBTBD8 prior to mRNA isolation. HUMAN GENE 1.0 ST ARRAY chips were used.