Mutations in ORC1, encoding the largest subunit of the origin recognition complex, cause microcephalic primordial dwarfism resembling Meier-Gorlin syndrome


Studies into disorders of extreme growth failure (for example, Seckel syndrome and Majewski osteodysplastic primordial dwarfism type II) have implicated fundamental cellular processes of DNA damage response signaling and centrosome function in the regulation of human growth. Here we report that mutations in ORC1, encoding a subunit of the origin recognition complex, cause microcephalic primordial dwarfism resembling Meier-Gorlin syndrome. We establish that these mutations disrupt known ORC1 functions including pre-replicative complex formation and origin activation. ORC1 deficiency perturbs S-phase entry and S-phase progression. Additionally, we show that Orc1 depletion in zebrafish is sufficient to markedly reduce body size during rapid embryonic growth. Our data suggest a model in which ORC1 mutations impair replication licensing, slowing cell cycle progression and consequently impeding growth during development, particularly at times of rapid proliferation. These findings establish a novel mechanism for the pathogenesis of microcephalic dwarfism and show a surprising but important developmental impact of impaired origin licensing.

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Figure 1: ORC1 expression and pre-RC complex assembly in ORC1-deficient cell lines from affected individuals.
Figure 2: ORC1-deficient cells fail to efficiently activate replication origins.
Figure 3: ORC1-deficient cells show slow S-phase progression.
Figure 4: ORC1-deficient cells show delayed G1 to S progression.
Figure 5: Depletion of Orc1 causes dwarfism in zebrafish.

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We thank the families and clinicians for their involvement; S. McKay, K. Erskine and the MRC HGU core sequencing service for advice and technical support; D. Fitzpatrick, J. Blow, E. Patton, V. van Heyningen, N. Hastie and T. Carr for discussions and comments; A. Sinclair for p294(oriP); A. Oliver for structural modeling; and S. Devroy for subject enrollment and sample collection. The A.P.J. laboratory is funded by the MRC and the Lister Insitute for Preventive Medicine, the M.O'D. laboratory is funded by Cancer Research UK and the MRC, and the P.A.J. laboratory is funded by the MRC, Association for International Cancer Research and the Wellcome Research Trust. A.P.J. is an MRC Senior Clinical Fellow and Lister Institute Prize fellow. M.O'D. is a CRUK Senior Cancer Research Fellow.

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L.S.B. and A.P.J. designed and performed the genetics experiments. A.K., A.L., C.-A.M., P.Y. and A.P.J. performed the zebrafish studies. S.W., T.S., C.K., M.O'D. and P.A.J. designed and performed the functional cell biology experiments. N.A.S., D.J., M.B. and C.W. provided clinical samples and data. P.A.J., A.P.J., L.S.B. and M.O'D. wrote the paper.

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Correspondence to Andrew P Jackson or Mark O'Driscoll.

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The authors declare no competing financial interests.

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Bicknell, L., Walker, S., Klingseisen, A. et al. Mutations in ORC1, encoding the largest subunit of the origin recognition complex, cause microcephalic primordial dwarfism resembling Meier-Gorlin syndrome. Nat Genet 43, 350–355 (2011).

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