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- Biallelic BUB1 mutations cause microcephaly, developmental delay, and variable effects on cohesion and chromosome segregationPublication . Carvalhal, Sara; Bader, Ingrid; Rooimans, Martin A.; Oostra, Anneke B.; Balk, Jesper A.; Feichtinger, René G.; Beichler, Christine; Speicher, Michael R.; van Hagen, Johanna M.; Waisfisz, Quinten; van Haelst, Mieke; Bruijn, Martijn; Tavares, Alexandra; Mayr, Johannes A.; Wolthuis, Rob M. F.; Oliveira, Raquel A.; de Lange, JobBudding uninhibited by benzimidazoles (BUB1) contributes to multiple mitotic processes. Here, we describe the first two patients with biallelic BUB1 germline mutations, who both display microcephaly, intellectual disability, and several patient-specific features. The identified mutations cause variable degrees of reduced total protein level and kinase activity, leading to distinct mitotic defects. Both patients' cells show prolonged mitosis duration, chromosome segregation errors, and an overall functional spindle assembly checkpoint. However, while BUB1 levels mostly affect BUBR1 kinetochore recruitment, impaired kinase activity prohibits centromeric recruitment of Aurora B, SGO1, and TOP2A, correlating with anaphase bridges, aneuploidy, and defective sister chromatid cohesion. We do not observe accelerated cohesion fatigue. We hypothesize that unresolved DNA catenanes increase cohesion strength, with concomitant increase in anaphase bridges. In conclusion, BUB1 mutations cause a neurodevelopmental disorder, with clinical and cellular phenotypes that partially resemble previously described syndromes, including autosomal recessive primary microcephaly, mosaic variegated aneuploidy, and cohesinopathies.
- Editorial: molecular mechanisms of cilia related diseasesPublication . Carvalhal, Sara; Carmona, Bruno; Tassin, Anne-Marie; Gonçalves, JoãoEukaryotic cilia are fascinating evolutionarily conserved microtubule-based organelles that protrude from the cell surface. In vertebrates, multiple types of motile and primary (immotile) cilia fulfill motility and signaling functions, critical for embryonic development and homeostasis of adult tissues. Importantly, perturbed cilia assembly and functions are associated with a growing number of diseases. This Research Topic gathers an update on recent progress made in understanding the molecular mechanisms of cilia-related diseases. Critically, understanding disease development has been facilitated by advances in technology. For example, the importance of omics techniques for monitoring the progression of cilia-associated rare diseases is showcased in the work of (Jeziorny et al.). This study applied an untargeted metabolomic approach using LC-QTOF-MS to study patients with Alström (ALMS) and Bardet-Biedl (BBS), which shared defective primary ciliary structures and found common molecular fingerprints between ALMS and BBS, and alterations in various lipid metabolites when comparing obese and healthy participants (Jeziorny et al.).
- Generation and characterization of two isogenic induced pluripotent stem cell lines from a young female with microcephaly carrying a compound heterozygous mutation in BUB1 genePublication . Ferreira, Anita; Calado, Sofia; Jorge, Xavier; Lange, Job de; Carvalhal, SaraMutations in the Budding uninhibited by benzimidazoles (BUB1) gene were recently associated with neurodevelopmental disorders (Carvalhal et al., 2022). Here, we describe the generation and characterization of two induced pluripotent stem cells (iPSC) clones from a young female with microcephaly. The patient carried two variants in the BUBfibroblast gene (OMIM # 602452), one (c.[2197dupG]; p.[D732fs*11]) paternally inherited and one (c.[2625+1G>A]; p.[V822_L875del] maternally inherited. The generated clones exhibit a normal karyotype (UALGi003-A) and trisomy 8 (UALGi003-B), express pluripotency markers, and differentiate into trilineage cells in vitro. These cell lines can be used to study neurodevelopment and the processes of chromosome segregation.
- Common mechanistic pathways in rare congenital syndromes with primary microcephalyPublication . Jorge, Xavier; Milagre, Ines; Ferreira, Anita; Calado, Sofia; Oliveira, Raquel; Carvalhal, SaraPrimary microcephaly is an often-seen phenotype in several rare congenital syndromes. It is characterised by a smaller brain size at birth compared to the norm. The causes of this malformation are not fully understood, but genetic testing suggests a connection with defective genes involved in mitotic regulation and proteins related to DNA repair and replication pathways. Cohesinopathies represent a group of rare syndromes, where several subtypes exhibit spontaneous railroad chromosomes and primary microcephaly. This includes Roberts Syndrome, Warsaw Breakage Syndrome and a recently characterised syndrome caused by mutations in the BUB1 gene. Currently, we are examining fibroblast cells from patients with these syndromes to identify common mechanistic pathways. In this context, we have identified a new promising candidate: Topoisomerase II alpha, a protein responsible for resolving of the DNA catenation both in the DNA replication and mitosis. Defective localisation of Topoisomerase II alpha may contribute to the observed mitotic defects in these cells. We are currently exploring the impact of these defects on brain development using reprogramming techniques to assess proper neuronal differentiation.