Loss-of-function variants in myocardin cause congenital megabladder in humans and mice
Arjan C. Houweling, … , Adrian S. Woolf, Esther E. Creemers
Arjan C. Houweling, … , Adrian S. Woolf, Esther E. Creemers
Published September 12, 2019
Citation Information: J Clin Invest. 2019;129(12):5374-5380. https://doi.org/10.1172/JCI128545.
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Concise Communication Muscle biology

Loss-of-function variants in myocardin cause congenital megabladder in humans and mice

Abstract

Myocardin (MYOCD) is the founding member of a class of transcriptional coactivators that bind the serum-response factor to activate gene expression programs critical in smooth muscle (SM) and cardiac muscle development. Insights into the molecular functions of MYOCD have been obtained from cell culture studies, and to date, knowledge about in vivo roles of MYOCD comes exclusively from experimental animals. Here, we defined an often lethal congenital human disease associated with inheritance of pathogenic MYOCD variants. This disease manifested as a massively dilated urinary bladder, or megabladder, with disrupted SM in its wall. We provided evidence that monoallelic loss-of-function variants in MYOCD caused congenital megabladder in males only, whereas biallelic variants were associated with disease in both sexes, with a phenotype additionally involving the cardiovascular system. These results were supported by cosegregation of MYOCD variants with the phenotype in 4 unrelated families by in vitro transactivation studies in which pathogenic variants resulted in abrogated SM gene expression and by the finding of megabladder in 2 distinct mouse models with reduced Myocd activity. In conclusion, we have demonstrated that variants in MYOCD result in human disease, and the collective findings highlight a vital role for MYOCD in mammalian organogenesis.

Authors

Arjan C. Houweling, Glenda M. Beaman, Alex V. Postma, T. Blair Gainous, Klaske D. Lichtenbelt, Francesco Brancati, Filipa M. Lopes, Ingeborg van der Made, Abeltje M. Polstra, Michael L. Robinson, Kevin D. Wright, Jamie M. Ellingford, Ashley R. Jackson, Eline Overwater, Rita Genesio, Silvio Romano, Letizia Camerota, Emanuela D’Angelo, Elizabeth J. Meijers-Heijboer, Vincent M. Christoffels, Kirk M. McHugh, Brian L. Black, William G. Newman, Adrian S. Woolf, Esther E. Creemers

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Figure 4

Myocd loss of function in mice causes the megabladder phenotype.

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Myocd loss of function in mice causes the megabladder phenotype. (A) Sc...
(A) Schematic representation of the MyocdΔLZ allele, in which 24 nucleotides are deleted in the LZ domain (p.I531_R539delinsM in NP_666498.2). (B–E) αSMA immunohistochemistry in 1-day-old neonates from Myocd+/– and MyocdΔLZ/+ crosses. (C) Compound heterozygosity (MyocdΔLZ/–; reminiscent of the alleles present in the affected individuals in family A) results in wall thinning of the bladder and lack of SM cells compared with the WT bladder wall (B). (D and E) Higher magnifications of WT and MyocdΔLZ/– bladder walls showing lack of αSMA-expressing muscle bundles in the putative detrusor layer, although expression appeared retained in myofibroblast-like cells in the lamina propria directly below the urothelium and in the rectum. (F) Schematic representation of the MyocdMgb allele. (G–J) Representative αSMA immunohistochemistry in P1 bladder of WT (G and H) and Myocdmgb/– compound heterozygote (I and J) (from a cross of Myocdmgb/+ and Myocd+/– mice). Note the severe bladder distention and absent detrusor muscle in the Myocdmgb/– bladder. Bl, bladder; In, intestine; Re, rectum; U, urethelium; S, submucosa; DM, detrusor muscle. Scale bars: 500 μm (B, C, G, and I); 100 μm (D, E, H, and J). (K) Myocd mRNA levels were quantified by qPCR using E15 bladders of WT, Myocd+/–, Myocdmgb/+, Myocdmgb/mgb, and Myocdmgb/– mice. The absolute numbers of embryos developing megabladder as a fraction of the total number of embryos analyzed are indicated above the graph and reveals a highly penetrant phenotype in the Myocdmgb/mgb and Myocdmgb/– mice.