A postnatal role for embryonic myosin revealed by MYH3 mutations that alter TGF\u03b2 signaling and cause autosomal dominant spondylocarpotarsal synostosis

Jennifer Zieba,Jessica X Chong,Ralph S Lachman,Tjitske Kleefstra,Deborah Nickerson,Kelly Heard,Kimberly N Forlenza,Dorothy K Grange,Merlin G Butler,Wenjuan Zhang,Jorge H Martin,Daniel H Cohn,Deborah Krakow,Michael Bamshad,Michael Regnier

doi:10.1038/srep41803

Abstract

Spondylocarpotarsal synostosis (SCT) is a skeletal disorder characterized by progressive vertebral, carpal and tarsal fusions, and mild short stature. The majority of affected individuals have an autosomal recessive form of SCT and are homozygous or compound heterozygous for nonsense mutations in the gene that encodes the cytoskeletal protein filamin B (FLNB), but a subset do not have FLNB mutations. Exome sequence analysis of three SCT patients negative for FLNB mutations identified an autosomal dominant form of the disease due to heterozygosity for missense or nonsense mutations in MYH3, which encodes embryonic myosin. Cells transfected with the MYH3 missense mutations had reduced TGFβ signaling, revealing a regulatory role for embryonic myosin in the TGFβ signaling pathway. In wild-type mice, there was persistent postnatal expression of embryonic myosin in the small muscles joining the neural arches of the spine suggesting that loss of myosin function in these muscles contribute to the disease. Our findings demonstrate that dominant mutations in MYH3 underlie autosomal dominant SCT, identify a postnatal role for embryonic myosin and suggest that altered regulation of signal transduction in the muscles within the spine may lead to the development of vertebral fusions.

Highlights

Polyphen-2 prediction Probably Damaging Probably Damaging — dominant form of SCT (AD SCT) has been described in an affected mother and son in whom mutations in both FLNB and Noggin were excluded[3], indicating that there is locus heterogeneity in SCT
In a Flnb knockout mouse model of SCT, we showed that progressive vertebral fusions occur through early degeneration, collapse, and eventual mineralization of the intervertebral disc (IVD)[5]
The vertebral fusions resulted in part from up regulation of both the Transforming Growth Factor β(TGFβ)and Bone Morphogenetic Protein (BMP) signaling pathways within the IVD5

Summary

Inheritance Dominant De novo Dominant Unknown Dominant Unknown

Polyphen-2 prediction Probably Damaging Probably Damaging — Table 1. Affected individuals from all three families were heterozygous for variants in MYH3, which encodes embryonic myosin heavy chain 3 (Table 1). Individual R06-109A was heterozygous for a de novo variant, c.1934T >G, predicted to result in a p.Phe645Cys substitution (Supplemental Fig. 1). The third affected individual, R12-336, was heterozygous for a frameshift deletion, c.2699delT (p.Leu900fs9), predicted to lead to a premature termination codon (Supplemental Fig. 1) These results suggest that mutations in MYH3 underlie AD SCT. Since affected individual R12-336 was ascertained in a cohort of FLNB negative SCT patients, two of whom had mutations in MYH3, we interpret the nonsense allele for embryonic myosin as likely to have phenotypic consequences. Following confirmation by Sanger sequence analyses (Supplemental Fig. 3), the mutated plasmids were transfected into human embryonic kidney (HEK) cells using the Lipofectamine 3000 Reagent Kit (ThermoFisher, L3000015).

No No Yes No No

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Additional Information