FBS Colloquia No.425Laboratory of Cancer Pathology

Analysis of the craniofacial phenotype of Schinzel-Giedion syndrome using Setbp1 mutant mice

Among genes encoding epigenetic regulators, a considerable number cause cancer when mutated somatically, yet give rise to severe developmental disorders when the same lesions are present in the germline. SETBP1 is a representative example: hotspot mutations within its degron motif are found in myeloid neoplasms, and, when present in the germline, cause Schinzel-Giedion syndrome (SGS). SGS is a congenital disorder characterized by distinctive craniofacial dysmorphism together with severe developmental delay and hydronephrosis. Although mutant SETBP1 escapes degradation and accumulates in cells throughout the body, the resulting pathology is confined to particular tissues, and the basis of this tissue selectivity has remained unresolved. Here we generated a conditional knock-in mouse carrying the D859N substitution, orthologous to human D868N, at the endogenous Setbp1 locus, which reproduced the phenotypes seen in patients, including calvarial hypoplasia and hydronephrosis. Noting that the craniofacial skeleton, unlike the axial skeleton, is derived almost entirely from neural crest cells (NCCs), and that the phenotypic spectrum of SGS overlaps broadly with that of the neurocristopathies, we restricted the mutation to NCCs; this reproduced the reduced calvarial mineralization and widened sutures observed in the systemic model. To define how the mutation perturbs gene regulation within the NCC lineage, we combined the allele with a reporter mouse in which Cre recombination switches fluorescence from EGFP to dsRed, isolated cells of the NCC lineage, and performed multi-omic analyses. NCC-derived mesenchymal stem cells were found to pass through a stage of elevated expression of ribosome biogenesis genes during osteoblast differentiation, and this progression was altered in mutant cells. Mutant SETBP1 localized to the nucleolus as well as the nucleoplasm, whereas the p53-dependent quality control pathway that normally operates under such conditions was not activated in mutant cells. In this colloquium, I will present our lineage-tracing platform and discuss how a single germline mutation causes disease through a cell lineage–specific vulnerability.