Loss-of-function variant in SPIN4 causes an X-linked overgrowth syndrome
Julian C. Lui, Jacob Wagner, Elaine Zhou, Lijin Dong, Kevin M. Barnes, Youn Hee Jee, Jeffrey Baron
Julian C. Lui, Jacob Wagner, Elaine Zhou, Lijin Dong, Kevin M. Barnes, Youn Hee Jee, Jeffrey Baron
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Research Article Development Genetics

Loss-of-function variant in SPIN4 causes an X-linked overgrowth syndrome

Abstract

Overgrowth syndromes can be caused by pathogenic genetic variants in epigenetic writers, such as DNA and histone methyltransferases. However, no overgrowth disorder has previously been ascribed to variants in a gene that acts primarily as an epigenetic reader. Here, we studied a male individual with generalized overgrowth of prenatal onset. Exome sequencing identified a hemizygous frameshift variant in Spindlin 4 (SPIN4), with X-linked inheritance. We found evidence that SPIN4 binds specific histone modifications, promotes canonical WNT signaling, and inhibits cell proliferation in vitro and that the identified frameshift variant had lost all of these functions. Ablation of Spin4 in mice recapitulated the human phenotype with generalized overgrowth, including increased longitudinal bone growth. Growth plate analysis revealed increased cell proliferation in the proliferative zone and an increased number of progenitor chondrocytes in the resting zone. We also found evidence of decreased canonical Wnt signaling in growth plate chondrocytes, providing a potential explanation for the increased number of resting zone chondrocytes. Taken together, our findings provide strong evidence that SPIN4 is an epigenetic reader that negatively regulates mammalian body growth and that loss of SPIN4 causes an overgrowth syndrome in humans, expanding our knowledge of the epigenetic regulation of human growth.

Authors

Julian C. Lui, Jacob Wagner, Elaine Zhou, Lijin Dong, Kevin M. Barnes, Youn Hee Jee, Jeffrey Baron

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Figure 6

Spin4 promotes Wnt/β-catenin signaling.

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Spin4 promotes Wnt/β-catenin signaling. (A) In HEK293T cells, Spin1 and ...
(A) In HEK293T cells, Spin1 and Spin4 WT (WT), but not frameshift variant (Mut), promotes Wnt signaling when cotransfected with β-catenin (1-way ANOVA; n = 10–15). Signals were represented in a luciferase activity ratio of firefly luciferase (from TOPFLASH or FOPFLASH) over renilla luciferase (for normalization of transfection efficiency). (B) SPIN4 WT, but not SPIN4 Mut, increased TOPFLASH signal when cotransfected with TCF1 and β-catenin. The induction was not observed, however, when cotransfected with TCF1 alone, suggesting the dependence on β-catenin expression (1-way ANOVA, n = 8–10). (C) In monolayer chondrocytes isolated from 1-week-old WT mice or Spin4 long deletion (KO), luciferase assay of TOPFLASH showed decreased baseline Wnt signaling activity in KO cells. This difference was abolished when mouse Spin4 was overexpressed in both cells, suggesting that the difference was due to a lack of endogenous Spin4 expression (1-way ANOVA, n = 9). (D) KO chondrocytes showed decreased expression of Spin4 and Axin2 but similar expression levels of Col2a1 and Col10a1 compared with WT chondrocytes. Expression of Dlx5, Rankl, and Cd4 were low, suggesting minimal contamination with osteoblast or bone marrow cells (Student’s t test, n = 5–7).