Polarity of myocardial cells during cardiac chamber formation – cardiopol

Heart failure is a major cause of death in industrial countries. Designing cell therapies for heart repair is therefore a topical issue. Many laboratories worldwide focus on the isolation and characterisation of potential cardiac stem cells. The identification of factors that improve cell differentiation and expansion has benefited from the analysis of heart development in vivo. However, the behaviour of cardiac cells, which underlies the growth of the myocardium, has been neglected and exploring this could provide new insight into regenerative cardiovascular medicine.
Previous work of the coordinator has shown that the growth of the myocardium is polarised, but it has remained unclear how this is achieved at the cellular level. How cardiac cell polarity regulates cell behaviour and ultimately the shape of the heart remains largely unexplored in mammals. We wish to decipher the mechanisms which underlie the polarity of cells in the heart and model the expansion of cardiac chambers using an interdisciplinary approach.
We propose to characterise, by immunostaining in 3D images of the embryonic heart, the orientation of cell behaviour, such as cell division and cell shape elongation, as well as the polarised localisation, within cells, of regulators of the mitotic spindle position. We have established conditions, which permit us to acquire a high number of images of the heart. Preliminary results support the hypothesis that myocardial cells and their behaviour are polarised. Studying the development of a complex 3D geometry such as the heart and studying the non-stereotyped behaviour of cells in mammals is ambitious. It requires sophisticated quantitative and statistical analyses, based on tools being developed in an existing interdisciplinary collaboration. These will be performed by a post-doc, who will be financed by the grant. We shall conduct functional studies using mutant mice to understand how disruption of polarity affects the overall heart shape and myocardial cell behaviour. We shall use pre-existing mutant mouse lines with impaired polarity signalling or mispositioning of the mitotic spindle. To understand how the polarised growth of the myocardium impacts heart morphogenesis, we shall design a computer model of cardiac chamber expansion. This model will be adapted from a pre-existing framework successfully implemented in the flower. We wish to examine how different aspects of cell behaviour integrate to generate shape. The variation of cell polarity with the shape of the chambers will be analysed, to determine how similar basic cell behaviour and similar polarity clues are tuned differently to generate distinct shapes. Finally, we wish to apply this knowledge of myocardial cell polarity to improve the culture of isolated cardiomyocytes and the growth of myocardial tissue in vitro.
We expect to identify new players in heart morphogenesis and we aim to characterise tools for controlling the behaviour of cardiac cells in vitro. This study should provide a better understanding of how polarity underlies the morphogenesis of a complex 3D geometry such as the mouse heart. This is important in a post-genomic era, to elucidate the way from the genotype to the phenotype. This is relevant to the diagnosis, and perhaps treatment, of congenital heart malformations.