TRRAP participates in embryonic development as demonstrated
TRRAP participates in embryonic development, as demonstrated by its binding with proteins regulating the Notch signaling pathway in fruit fly, the Ras signaling pathway in C. elegans, or the Wnt signaling pathway in 293T cells. Therefore we suspect that TRRAP variants, more especially those falling within the 1031–1159 region, perturb the interactions with at least one of these developmental signaling pathways; such a perturbance would explain the multiple malformations observed in about half of the affected individuals.
In yeast, a series of ∼100 Benzamil deletion mutants in the ortholog tra1 showed reduced or complete loss of viability. Most deletions impaired coactivator complex assembly, notably the ones encompassing the homologous 1031–1159 cluster (mutants Δ13–Δ14), as well as the regions homologous to those containing variants p.Leu805Phe, p.Phe860Leu, and p.Arg893Leu (mutants Δ11–Δ12) and the p.Arg3757Gln variant (mutant Δ39). In contrast, mutants Δ21–Δ22 encompassing the region homologous to the cluster associated with fewer malformations (codons 1859–1932) were viable, which might help explain the milder clinical phenotype associated with variants within this cluster. In mice, Trrap knockout leads to early embryonic lethality, and a neural-cell-specific conditional Trrap knockout line revealed premature differentiation of neural progenitors, depletion of progenitor pools, and a significant reduction in cortical thickness. These mice exhibited striking microcephaly, in agreement with what we observed in half of the individuals in our study cohort, primarily those with variants in the 1031–1159 cluster.
In summary, we report evidence that variants in TRRAP are associated with a pleiotropic neurodevelopmental syndrome with a potential genotype-phenotype correlation. Our functional data highlight an enrichment of genes related to neuronal function and ion transport. This enrichment could underline the pathophysiology of the disease. Future in vitro and in vivo studies on variants inside and outside the main cluster will be required if we are to determine which gene expression changes are connected to which TRRAP-related specific phenotypes.
Declaration of Interests
Acknowledgments We would like to thank all families for participating in this study. This work was supported in part by grants from: the French Ministry of Health and the Health Regional Agency from Poitou-Charentes (HUGODIMS, 2013, RC14_0107) to S.B.; the National Institute of Neurological Disorders and Stroke (The Epilepsy Phenome/Genome Project NS053998; Epi4K NS077364, NS077274, NS077303, and NS077276) to D.L. and D.B.G.; the National Institutes of Health/Eunice Kennedy Shriver National Institute of Child Health and Human Development grant (HD064667) to D.A.S.; NINDS R35 NS105078 to J.R.L.; the National Human Genome Research Institute (NHGRI) and National Heart, Lung, and Blood Institute (NHLBI) to the Baylor-Hopkins Center for Mendelian Genomics (UM1 HG006542); NHGRI K08 HG008986 to J.E.P.; the Duke Genome Sequencing Clinic to V.S. and J.S.; the intramural research program of the NHGRI (grant HG200328 12) to L.G.B., J.J.J., and J.C.S.; the US National Institute of Mental Health grant R01MH101221 to E.E.E.; the Kids Brain Health Network and Dart NeuroScience to F.B.; and Mining for Miracles, British Columbia Children’s Hospital Foundation, and Genome British Columbia to the CAUSES Study. We thank the Canadian Institutes of Health Research (CIHR) and Fonds de la recherche en santé du Québec (FRSQ) for clinician-scientist awards to P.M.C.; and the Mayo Clinic Center for Individualized Medicine (CIM) for supporting this research through the CIM Investigative and Functional Genomics Program. We are grateful to the members of the Canadian Center for Computational Genomics and the McGill University and Génome Québec Innovation Center for their help in bioinformatics analysis.