hnRNP U protein is required for normal pre-mRNA splicing and postnatal heart development and function

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 112; no. 23; pp. E3020 - E3029
• Main Authors: Ye, Junqiang, Beetz, Nadine, O’Keeffe, Sean, Tapia, Juan Carlos, Macpherson, Lindsey, Chen, Weisheng V., Bassel-Duby, Rhonda, Olson, Eric N., Maniatis, Tom
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 09.06.2015; National Acad Sciences
• Series: PNAS Plus
• Subjects: alternative splicing; Alternative Splicing - physiology; Animals; Biological Sciences; Calcium - metabolism; calcium-binding proteins; Calcium-Binding Proteins - metabolism; Cardiomyocytes; cardiomyopathy; gene expression; genes; Glycosylation; heart; Heart - growth & development; Heart - physiology; Heterogeneous-Nuclear Ribonucleoprotein U - genetics; Heterogeneous-Nuclear Ribonucleoprotein U - physiology; knockout mutants; Membrane Proteins - metabolism; Mice; Mice, Knockout; Mixed Function Oxygenases - metabolism; Muscle Proteins - metabolism; Mutation; PNAS Plus; Proteins; Ribonucleic acid; ribonucleoproteins; RNA; RNA Precursors - metabolism; RNA, Messenger - metabolism; Rodents; Sarcomeres - metabolism; sarcoplasmic reticulum; heart development; RNA-seq; alternative splicing; N-glycosylation; dilated cardiomyopathy
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1508461112

Significance We studied the physiological function of the heterogeneous nuclear ribonucleoprotein U (hnRNP U) by generating a conditional knockout mouse in which the Hnrnpu gene is deleted in the heart. We found that hnRNP U is required for normal pre-mRNA splicing and postnatal heart development and function. Mutant mice develop severe dilated cardiomyopathy and die 2 wk after birth. Phenotypic characterization of mutant hearts coupled with RNA-seq data analyses revealed that mutant hearts display multiple cardiac defects as a result of misregulated gene expression and abnormal pre-mRNA splicing. We also identified the sarcoplasmic reticulum membrane protein Junctin as a splicing target of hnRNP U and provide an interesting example of alternative splicing in controlling the modification and function of proteins. We report that mice lacking the heterogeneous nuclear ribonucleoprotein U (hnRNP U) in the heart develop lethal dilated cardiomyopathy and display numerous defects in cardiac pre-mRNA splicing. Mutant hearts have disorganized cardiomyocytes, impaired contractility, and abnormal excitation–contraction coupling activities. RNA-seq analyses of Hnrnpu mutant hearts revealed extensive defects in alternative splicing of pre-mRNAs encoding proteins known to be critical for normal heart development and function, including Titin and calcium/calmodulin-dependent protein kinase II delta ( Camk2d ). Loss of hnRNP U expression in cardiomyocytes also leads to aberrant splicing of the pre-mRNA encoding the excitation–contraction coupling component Junctin. We found that the protein product of an alternatively spliced Junctin isoform is N -glycosylated at a specific asparagine site that is required for interactions with specific protein partners. Our findings provide conclusive evidence for the essential role of hnRNP U in heart development and function and in the regulation of alternative splicing.