Ewelina Bukowska-Olech, Robert Schöpflin, Verena Heinrich, Magdalena Socha, Martin Franke, Varun K. A. Sreenivasan, Uirá Souto Melo, Inga Nagel, Cristina López, Aleksander Jamsheer, Martin Vingron, Anna Sowińska-Seidler, Stefan Mundlos, Nicolas Gruchy, Bjørt K Kragesteen, Malte Spielmann, Department of Medical Genetics, Poznan University of Medical Sciences [Poland] (PUMS), Max Planck Institute for Molecular Genetics (MPIMG), Max-Planck-Gesellschaft, Institute for Medical Genetics and Human Genetics, Charité - UniversitätsMedizin = Charité - University Hospital [Berlin], Department of Immunology, Weizmann Institute of Science [Rehovot, Israël], Centro Andaluz de Biología del Desarrollo, Consejo Superior de Investigaciones Científicas, Institute of Human Genetics, Christian-Albrechts University and University Hospital Schleswig-Holstein, Campus Kiel, Service de Génétique [CHU Caen], CHU Caen, Normandie Université (NU)-Tumorothèque de Caen Basse-Normandie (TCBN)-Normandie Université (NU)-Tumorothèque de Caen Basse-Normandie (TCBN)-Université de Caen Normandie (UNICAEN), Normandie Université (NU), Biologie, génétique et thérapies ostéoarticulaires et respiratoires (BIOTARGEN), Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU), Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Institute of Human Genetic, Universitätsklinikum Schleswig Holstein Campus Lübeck and University of Lübecks, Centers for Medical Genetics GENESIS, Polish National Agency for Academic Exchange, Generalitat de Catalunya, European Commission, National Science Centre (Poland), German Research Foundation, and Max Planck Society
Copy-number variations (CNVs) are a common cause of congenital limb malformations and are interpreted primarily on the basis of their effect on gene dosage. However, recent studies show that CNVs also influence the 3D genome chromatin organization. The functional interpretation of whether a phenotype is the result of gene dosage or a regulatory position effect remains challenging. Here, we report on two unrelated families with individuals affected by bilateral hypoplasia of the femoral bones, both harboring de novo duplications on chromosome 10q24.32. The ∼0.5 Mb duplications include FGF8, a key regulator of limb development and several limb enhancer elements. To functionally characterize these variants, we analyzed the local chromatin architecture in the affected individuals’ cells and re-engineered the duplications in mice by using CRISPR-Cas9 genome editing. We found that the duplications were associated with ectopic chromatin contacts and increased FGF8 expression. Transgenic mice carrying the heterozygous tandem duplication including Fgf8 exhibited proximal shortening of the limbs, resembling the human phenotype. To evaluate whether the phenotype was a result of gene dosage, we generated another transgenic mice line, carrying the duplication on one allele and a concurrent Fgf8 deletion on the other allele, as a control. Surprisingly, the same malformations were observed. Capture Hi-C experiments revealed ectopic interaction with the duplicated region and Fgf8, indicating a position effect. In summary, we show that duplications at the FGF8 locus are associated with femoral hypoplasia and that the phenotype is most likely the result of position effects altering FGF8 expression rather than gene dosage effects., M.S. and A.S.-S. were supported by the Polish National Science Centre (UMO-2016/23/N/NZ2/02362 to M.S. and UMO-2016/21/D/NZ5/00064 to A.S.-S.). A.S.-S. was also supported by the Polish National Science Centre scholarship for PhD students (UMO-2013/08/T/NZ2/00027). C.L. is supported by postdoctoral Beatriu de Pinós from Secretaria d’Universitats I Recerca del Departament d’Empresa i Coneixement de la Generalitat de Catalunya and by the Marie Sklodowska-Curie COFUND program from H2020 (2018-BP-00055). A.J. was supported by the Polish National Science Centre (UMO-2016/22/E/NZ5/00270) as well as the Polish National Centre for Research and Development (LIDER/008/431/L-4/12/NCBR/2013). M.S. is supported by grants from the Deutsche Forschungsgemeinschaft (DFG) (SP1532/3-1, SP1532/4-1, and SP1532/5-1), the Max Planck Foundation, and the Deutsches Zentrum für Luft- und Raumfahrt (DLR 01GM1925).