Amsterdam UMC, University of Amsterdam, Department of Medical Biology, Amsterdam Cardiovascular Sciences, Amsterdam, Netherlands
Roeland MH Merks
Mathematical Institute, Leiden University, Leiden, Netherlands; Origins Center, Leiden University, Leiden, Netherlands; Institute of Biology, Leiden University, Leiden, Netherlands
Hubrecht Institute-KNAW and University Medical Center Utrecht, Utrecht, Netherlands; Department of Pediatric Cardiology, Division of Pediatrics, University Medical Center Utrecht, Utrecht, Netherlands
Organ laterality refers to the left-right asymmetry in disposition and conformation of internal organs and is established during embryogenesis. The heart is the first organ to display visible left-right asymmetries through its left-sided positioning and rightward looping. Here, we present a new zebrafish loss-of-function allele for tbx5a, which displays defective rightward cardiac looping morphogenesis. By mapping individual cardiomyocyte behavior during cardiac looping, we establish that ventricular and atrial cardiomyocytes rearrange in distinct directions. As a consequence, the cardiac chambers twist around the atrioventricular canal resulting in torsion of the heart tube, which is compromised in tbx5a mutants. Pharmacological treatment and ex vivo culture establishes that the cardiac twisting depends on intrinsic mechanisms and is independent from cardiac growth. Furthermore, genetic experiments indicate that looping requires proper tissue patterning. We conclude that cardiac looping involves twisting of the chambers around the atrioventricular canal, which requires correct tissue patterning by Tbx5a.
