Abstract
The fundamental importance of the proteoglycan versican to early heart formation was clearly demonstrated by the Vcan null mouse called heart defect (hdf). Total absence of the Vcan gene halts heart development at a stage prior to the heart’s pulmonary/aortic outlet segment growth. This creates a problem for determining the significance of versican’s expression in the forming valve precursors and vascular wall of the pulmonary and aortic roots. This study presents data from a mouse model, Vcan (tm1Zim), of heart defects that results from deletion of exon 7 in the Vcan gene. Loss of exon 7 prevents expression of two of the four alternative splice forms of the Vcan gene. Mice homozygous for the exon 7 deletion survive into adulthood, however, the inability to express the V2 or V0 forms of versican results in ventricular septal defects, smaller cushions/valve leaflets with diminished myocardialization and altered pulmonary and aortic outflow tracts. We correlate these phenotypic findings with a large-scale differential protein expression profiling to identify compensatory alterations in cardiac protein expression at E13.5 post coitus that result from the absence of Vcan exon 7. The Vcan (tm1Zim) hearts show significant changes in the relative abundance of several cytoskeletal and muscle contraction proteins including some previously associated with heart disease. These alterations define a protein fingerprint that provides insight to the observed deficiencies in pre-valvular/septal cushion mesenchyme and the stability of the myocardial phenotype required for alignment of the outflow tract with the heart ventricles.
Highlights
During embryonic development, the extracellular matrix plays a central role in restructuring the single heart tube into a mature multi-chambered organ
An abnormal relationship was observed between the aortic and pulmonary roots in the mutant hearts. These structural defects suggested developmental alterations in the mutants at or around embryonic stage 13.5 pc when there is a closure of membranous portion of the interventricular septum and the cardiac outlet is integrated into the central cushions [43]
To morphologically assess any detectable changes in versican and other specific Extracellular Matrix (ECM) markers that result from the loss of the V2/V0 splice forms we evaluated the structures in adult hearts (5 K weeks postnatal) by confocal indirect immunofluorescence
Summary
The extracellular matrix plays a central role in restructuring the single heart tube into a mature multi-chambered organ. The exons encode modular protein domains whose presence in the protein core is regulated by alternative splicing of the mRNA [8,9]. At least 4 different mRNA splice forms (V0, V1, V2 and V3) have been identified in adult tissue and are produced by the alternative splicing of exons 7 and 8 (Fig. 1). Several studies of expression have shown that these alternatively spliced mRNA forms are differentially expressed in specific tissues types, e.g. brain, smooth muscle, tumors, suggesting that the regulation of functional domains within versican are required for differentiation and persistence of a tissue’s phenotype [9,10,11,12,13,14,15]. Proteolytic processing of versican occurs during changes in the vascular system [16,17,18] and during critical stages of heart development [19,20,21]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
