Loss-of-function mouse and zebrafish models of TCOF1, POLR1B, POLR1C or POLR1D homologs exhibit extensive p53 dependent neuroepithelium and neural crest cell apoptosis, which presages hypoplasia of the craniofacial skeleton, mimicking the characteristic features of TCS in humans (Dixon et al., 2006; Jones et al., 2008; Noack Watt et al., 2016; Sanchez et al., 2020). The gene discussed is POLR1B; the disease is Treacher-Collins syndrome.