MKS1 regulates ciliary INPP5E levels in Joubert syndrome.
BACKGROUND
Joubert syndrome (JS) is a recessive ciliopathy characterised by a distinctive brain malformation 'the molar tooth sign'. Mutations in >27 genes cause JS, and mutations in 12 of these genes also cause Meckel-Gruber syndrome (MKS). The goals of this work are to describe the clinical features of MKS1-related JS and determine whether disease causing MKS1 mutations affect cellular phenotypes such as cilium number, length and protein content as potential mechanisms underlying JS.


METHODS
We measured cilium number, length and protein content (ARL13B and INPP5E) by immunofluorescence in fibroblasts from individuals with MKS1-related JS and in a three-dimensional (3D) spheroid rescue assay to test the effects of disease-related MKS1 mutations.


RESULTS
We report MKS1 mutations (eight of them previously unreported) in nine individuals with JS. A minority of the individuals with MKS1-related JS have MKS features. In contrast to the truncating mutations associated with MKS, all of the individuals with MKS1-related JS carry ≥ 1 non-truncating mutation. Fibroblasts from individuals with MKS1-related JS make normal or fewer cilia than control fibroblasts, their cilia are more variable in length than controls, and show decreased ciliary ARL13B and INPP5E. Additionally, MKS1 mutant alleles have similar effects in 3D spheroids.


CONCLUSIONS
MKS1 functions in the transition zone at the base of the cilium to regulate ciliary INPP5E content, through an ARL13B-dependent mechanism. Mutations in INPP5E also cause JS, so our findings in patient fibroblasts support the notion that loss of INPP5E function, due to either mutation or mislocalisation, is a key mechanism underlying JS, downstream of MKS1 and ARL13B.
Department of Nephrology and Hypertension, University Medical Center Utrecht, Utrecht, The Netherlands.
Gisela G
GG
Slaats
Department of Pediatrics, University of Washington, Seattle, Washington, USA.
Christine R
CR
Isabella
Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands.
Hester Y
HY
Kroes
Department of Pediatrics, University of Washington, Seattle, Washington, USA.
Jennifer C
JC
Dempsey
Department of Nephrology and Hypertension, University Medical Center Utrecht, Utrecht, The Netherlands.
Hendrik
H
Gremmels
Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands.
Glen R
GR
Monroe
Department of Pediatrics, University of Washington, Seattle, Washington, USA.
Ian G
IG
Phelps
Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands.
Karen J
KJ
Duran
Department of Pediatrics, University of Washington, Seattle, Washington, USA Division of Integrated Cancer Genomics, Translational Genomics Research Institute, Phoenix, Arizona, USA.
Jonathan
J
Adkins
Department of Pediatrics, University of Washington, Seattle, Washington, USA.
Sairam A
SA
Kumar
Department of Pediatrics, University of Washington, Seattle, Washington, USA.
Dana M
DM
Knutzen
Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands.
Nine V
NV
Knoers
Department of Medical Genetics, Children's Hospitals & Clinics of Minnesota, Minneapolis, Minnesota, USA.
Nancy J
NJ
Mendelsohn
Department of Child, Adolescent and Developmental Neurology, University Children's Hospital Ljubljana, Ljubljana, Slovenia.
David
D
Neubauer
Department of Neurology, Children's Hospital of Athens "P. and A. Kyriakou", Athens, Greece.
Sotiria D
SD
Mastroyianni
West Midlands Regional Genetics Service, Birmingham Women's Hospital, Birmingham, UK.
Julie
J
Vogt
Department of Clinical Genetics, Liverpool Hospital, Liverpool, Australia.
Lisa
L
Worgan
Medical Genetics Program, Department of Pediatrics, London Health Science Centre, University of Western Ontario, London, Ontario, Canada.
Natalya
N
Karp
Division of Clinical and Metabolic Genetics, Department of Paediatrics, The Hospital for Sick Children, Toronto, Ontario, Canada.
Sarah
S
Bowdin
Department of Pediatrics, University of Washington, Seattle, Washington, USA.
Ian A
IA
Glass
Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA.
Melissa A
MA
Parisi
Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, Michigan, USA.
Edgar A
EA
Otto
Section of Ophthalmology and Neuroscience, Leeds Institutes of Molecular Medicine, University of Leeds, Leeds, UK.
Colin A
CA
Johnson
Division of Nephrology, Boston Children's Hospital, Boston, Massachusetts, USA Howard Hughes Medical Institute, Chevy Chase, Maryland, USA.
Friedhelm
F
Hildebrandt
Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands.
Gijs
G
van Haaften
Department of Nephrology and Hypertension, University Medical Center Utrecht, Utrecht, The Netherlands.
Rachel H
RH
Giles
Department of Pediatrics, University of Washington, Seattle, Washington, USA Seattle Children's Research Institute, Seattle, Washington, USA.
Dan
D
Doherty
D020727:ADP-Ribosylation Factors / Q000378:metabolism; D000015:Abnormalities, Multiple / Q000175:diagnosis / Q000235:genetics* / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000473:pathology; D002478:Cells, Cultured; D002531:Cerebellum / Q000002:abnormalities* / Q000378:metabolism; D002923:Cilia / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D005091:Exons; D005124:Eye Abnormalities / Q000175:diagnosis / Q000235:genetics* / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D005786:Gene Expression Regulation; D006801:Humans; D052177:Kidney Diseases, Cystic / Q000175:diagnosis / Q000235:genetics* / Q000378:metabolism*; D008279:Magnetic Resonance Imaging; D051379:Mice; D008954:Models, Biological; D009154:Mutation; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D011485:Protein Binding; D021381:Protein Transport; D011506:Proteins / Q000235:genetics* / Q000378:metabolism*; D012160:Retina / Q000002:abnormalities* / Q000378:metabolism; D014057:Tomography, X-Ray Computed; D000099182:Phosphoinositide 5-Phosphatases
D020727:ADP-Ribosylation Factors; D010744:Phosphoric Monoester Hydrolases; D011506:Proteins; D000099182:Phosphoinositide 5-Phosphatases; C509165:MKS1 protein, human; C530391:ARL13B protein, human
Cell biology; Genetics