Structure and function relationship of Zebrafish embryonic heart from confocal microscopy images

Confocal microscopy enables us to track myocytes in the embryonic zebrafish heart. The Zeiss LSM 5 Live high speed confocal microscope has been used to take optical sections (at 3 µm intervals and 151 frames per second) through a fluorescently labeled zebrafish heart at two developmental stages (26 and 34 hours post fertilization (hpf)). This data provides unique information allowing us to conjecture on the morphology and biomechanics of the developing vertebrate heart. Nevertheless, the myocytes, whose positions could be determined in a reliable manner, were located sparsely and mostly in one side of the heart tube. This difficulty was overcome using computational methods, that give longitudinal, radial and circumferential displacements of the myocytes as well as their contractile behavior. Applied strain analysis has shown that in the early embryonic heart tube, only the caudal region (near the in-flow) and another point in the middle of the tube can be active; the rest appears to be mostly passive. This statement is based on the delay between major strain and displacement which a material point experiences. Wave-like propagation of all three components of the displacement, especially in the circumferential direction, as well as the almost-periodic changes of the maximum strain support the hypothesis of helical muscle structure embedded in the tube. Changes of geometry in the embryonic heart after several hours are used to verify speculations about the structure based on the earlier images and aforementioned methods.