In this project, we are studying C1orf131 that we identified as a novel gene involved in intellectual disability. The protein product plays a crucial role in maintaining the structural integrity of the nucleolus. It seems to be essential for a normal brain development and function. A better understanding of the nucleolar and mitotic function of C1orf131 will shed light on the cellular processes disrupted in C1orf131-mutated individuals. Data obtained from this study will give us an unprecedented opportunity to gain new insights into the gene regulatory networks required to form an optimally functional brain.
Intellectual disability (ID) is characterized by substantial limitations in both intellectual functioning and adaptive behavior. Its worldwide prevalence is estimated to range from 1% to 3%, which casts a serious socio-economic burden on societies. Based on the inheritance patterns, ID is classified into X-linked, autosomal recessive (ARID) and dominant. We studied a Pakistani family featuring ARID and identified linkage regions with a maximum possible LOD score of 2.4 on chromosomes 1, 2, 15 and 21. Whole-exome sequencing (WES) of two affected members revealed a missense mutation (NM_152379.3;c.112G>A; p.Asp38Asn) in C1orf131 located in the linkage region on chromosome 1. The mutated residue is highly conserved and its substitution is predicted to be pathogenic by several in silico tools. Virtually nothing has been reported about C1orf131 or its protein product. Our preliminary data suggest that it is a novel nucleolar component that relocates to the chromosomal periphery during mitosis. Depletion of the protein as observed in both patient fibroblasts or cells treated with siRNA resulted in distorted nucleoli. Intriguingly, pulldown data also showed that it interacts with several nucleolar and centrosomal proteins.
Here we propose to explore the potential involvement of the C1orf131 protein in nucleolar functions and cell cycle progression and to study their impairment. We also aim to investigate its role in neurogenesis by generating single-cell RNA sequencing (scRNA-seq) data of cerebral organoids, generated from patient-derived fibroblasts via induced pluripotent stem cells (iPSC). These data will allow us to dissect the progenitor/neuronal cell ratio and progenitor-to-neuron lineage relationships. Assuming high relevance for their etiology, we are confident to elucidate yet unknown mechanisms underlying ARID and microcephaly.
The main focus of our research is to unravel genetic causes of neurodevelopmental disorders and to explore the consequences of the identified mutations. In the last decade, we have provided new insights into the genetic etiology of families afflicted with primary microcephaly (MCPH), microcephalic primordial dwarfism (MPD) and Filippi syndrome (FS) using state-of-the-art genetic, biochemical and cell-biological methods (Table 1). Somatic cells of a patient from a Pakistani MCPH family with a homozygous truncating frame shift mutation (c.970delC, p.Gln324Serfs*2) of CEP135 showed characteristic features of aberrant centrosomes like multiple or fragmented centrosomes along with disorganized microtubules (Figure 1A). We also found a homozygous nonsense mutation (NM_017668.2; c.658C>T, p.Arg220*) of NDE1 in an
|No||Disorder||Gene||Consequences of the identified mutations|
|1||MCPH||CEP135||Centrosomal dysfunctions, multiple and fragmented centrosomes, disorganized microtubules.|
|2||MCPH||CDK6||Association with centrosome, depletion causes supernumerary centrosomes, disorganized microtubules.|
|3||MCPH||KIF14||Midbody protein, mutation triggered loss of CRIK (citron rho-interacting kinase) at the midbody that consequently impaired cytokinesis and led to apoptosis.|
|4||MCPH||NUP37||Component of outer rings of the nuclear pore complex (NPC), mutation altered the amount and localization of other NPCs — NUP160 and NUP133 — and decreased the number of nuclear pores.|
|5||MPD||PLK4||Mutation activates a novel cryptic splice acceptor site and introduces a premature termination codon. It impaired centriole biogenesis and resulted in a monopolar configuration, centriole loss and defective spindle formation.|
|6||FS||CKAP2L||First genetic cause of Filippi syndrome, mutation caused disorganized spindle microtubules, multipolar configurations and defects in chromosome segregation.|
|7||ARID||C1orf131||New ARID gene encoding a novel nucleolar protein, its depletion causes a distortion of the nucleoli.|
MCPH patient of Yemeni origin. Primary fibroblasts of the patient showed an impaired localization pattern of the mutant protein (NudE) in form of aggregates within the nucleus as well as faint staining at the centrosomes as detected by ϒ-tubulin (Figure 1B). Investigation of CENPJ-mutated cells(NM_018451.4: c.18delC, p.Ser7Profs*2) resulted in the impairment of centriole (Figure 1C, left panel) and centrosome (Figure 1C, right panel) duplication, which depicts the role of CENP-J in centriole duplication (Figure 1C). One of our most recent findings is the identification of novel MCPH gene named KIAA0408 which encodes a novel centrosomal protein (Figure 1D).
Maria Asif (Doctoral student)
Arwa Khayyat (Doctoral student)
Syeda Seema Waseem (Doctoral student)
Martina Munck (technician)