title: CDK6 associates with the centrosome during mitosis and is mutated in a large Pakistani family with primary microcephaly.
abstract: Autosomal recessive primary microcephaly (MCPH) is characterized by reduced head circumference, reduction in the size of the cerebral cortex with otherwise grossly normal brain structure and variable intellectual disability. MCPH is caused by mutations of 11 different genes which code for proteins implicated in cell division and cell cycle regulation. We studied a consanguineous eight-generation family from Pakistan with ten microcephalic children using homozygosity mapping and found a new MCPH locus at HSA 7q21.11-q21.3. Sanger sequencing of the most relevant candidate genes in this region revealed a homozygous single nucleotide substitution c.589G>A in CDK6, which encodes cyclin-dependent kinase 6. The mutation changes a highly conserved alanine at position 197 into threonine (p.Ala197Thr). Post hoc whole-exome sequencing corroborated this mutation's identification as the causal variant. CDK6 is an important protein for the control of the cell cycle and differentiation of various cell types. We show here for the first time that CDK6 associates with the centrosome during mitosis; however, this was not observed in patient fibroblasts. Moreover, the mutant primary fibroblasts exhibited supernumerary centrosomes, disorganized microtubules and mitotic spindles, an increased centrosome nucleus distance, reduced cell proliferation and impaired cell motility and polarity. Upon ectopic expression of the mutant protein and knockdown of CDK6 through shRNA, we noted similar effects. We propose that the identified CDK6 mutation leads to reduced cell proliferation and impairs the correct functioning of the centrosome in microtubule organization and its positioning near the nucleus which are key determinants during neurogenesis.
authors.affiliation: Cologne Center for Genomics (CCG).
authors.forename: Muhammad S
authors.initials: MS
authors.lastname: Hussain
authors.forename: Shahid M
authors.initials: SM
authors.lastname: Baig
authors.forename: Sascha
authors.initials: S
authors.lastname: Neumann
authors.forename: Vivek S
authors.initials: VS
authors.lastname: Peche
authors.forename: Sandra
authors.initials: S
authors.lastname: Szczepanski
authors.forename: Gudrun
authors.initials: G
authors.lastname: Nürnberg
authors.forename: Muhammad
authors.initials: M
authors.lastname: Tariq
authors.forename: Muhammad
authors.initials: M
authors.lastname: Jameel
authors.forename: Tahir N
authors.initials: TN
authors.lastname: Khan
authors.forename: Ambrin
authors.initials: A
authors.lastname: Fatima
authors.forename: Naveed A
authors.initials: NA
authors.lastname: Malik
authors.forename: Ilyas
authors.initials: I
authors.lastname: Ahmad
authors.forename: Janine
authors.initials: J
authors.lastname: Altmüller
authors.forename: Peter
authors.initials: P
authors.lastname: Frommolt
authors.forename: Holger
authors.initials: H
authors.lastname: Thiele
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Höhne
authors.forename: Gökhan
authors.initials: G
authors.lastname: Yigit
authors.forename: Bernd
authors.initials: B
authors.lastname: Wollnik
authors.forename: Bernd A
authors.initials: BA
authors.lastname: Neubauer
authors.forename: Peter
authors.initials: P
authors.lastname: Nürnberg
authors.forename: Angelika A
authors.initials: AA
authors.lastname: Noegel
mesh_terms: D018385:Centrosome / Q000378:metabolism*; D002874:Chromosome Mapping; D002897:Chromosomes, Human, Pair 7 / Q000235:genetics; D051361:Cyclin-Dependent Kinase 6 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005260:Female; D056726:Genetic Association Studies; D006801:Humans; D008607:Intellectual Disability / Q000235:genetics* / Q000503:physiopathology; D008297:Male; D008831:Microcephaly / Q000235:genetics* / Q000503:physiopathology; D008870:Microtubules / Q000235:genetics / Q000378:metabolism; D008938:Mitosis / Q000235:genetics*; D009154:Mutation; D010375:Pedigree; D020641:Polymorphism, Single Nucleotide; D011487:Protein Conformation
chemical_list: C495911:CDK6 protein, human; D051361:Cyclin-Dependent Kinase 6