Charged multivesicular body protein 1A (CHMP1A; also known as chromatin-modifying protein 1A) is a member of the ESCRT-III (endosomal sorting complex required for transport-III) complex but is also suggested to localize to the nuclear matrix and regulate chromatin structure. Here, we show that loss-of-function mutations in human CHMP1A cause reduced cerebellar size (pontocerebellar hypoplasia) and reduced cerebral cortical size (microcephaly). CHMP1A-mutant cells show impaired proliferation, with increased expression of INK4A, a negative regulator of stem cell proliferation. Chromatin immunoprecipitation suggests loss of the normal INK4A repression by BMI in these cells. Morpholino-based knockdown of zebrafish chmp1a resulted in brain defects resembling those seen after bmi1a and bmi1b knockdown, which were partially rescued by INK4A ortholog knockdown, further supporting links between CHMP1A and BMI1-mediated regulation of INK4A. Our results suggest that CHMP1A serves as a critical link between cytoplasmic signals and BMI1-mediated chromatin modifications that regulate proliferation of central nervous system progenitor cells.
Bibliographical noteFunding Information:
We thank the individuals and their families reported herein for their participation in this research. We thank M. van Lohuizen (Netherlands Cancer Institute) for providing the Bmi1knockout mice, A. Wagers for help with breeding the Bmi1knockout mice and P. Baas for sharing human DNA samples. This research was supported by grants from the US National Institute of Neurological Disorders and Stroke (NINDS; R01NS035129) and the Fogarty International Center (R21TW008223) to C.A.W., the Dubai Harvard Foundation for Medical Research, the Simons Foundation and the Manton Center for Orphan Disease Research. G.H.M. was supported by the Young Investigator Award of the National Alliance for Research on Schizophrenia and Depression (NARSAD) as a NARSAD Lieber Investigator. V.S.G. is supported by the Medical Scientist Training Program of Harvard Medical School, with financial support from the US National institute of General Medical Sciences (NIGMS). C.A.W. and L.I.Z. are investigators of the Howard Hughes Medical Institute. Microscopy and image analyses were performed with support from the Cellular Imaging Core of the Boston Children’s Hospital Intellectual and Developmental Disabilities Research Center.