Cardiac Looping und die frühe Topogenese der AV-Region: Untersuchung an Hühnerembryonen
Cardiac looping and the early topogenesis of the atrioventricular canal (avc) in the embryonic chick heart
by Thomas Reichel
Date of Examination:2017-08-22
Date of issue:2017-08-10
Advisor:PD Dr. Jörg Männer
Referee:Prof. Dr. Theodor Tirilomis
Referee:PD Dr. Claudius Jacobshagen
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Abstract
English
The early embryonic heart is a tubular structure that forms by merging of left and right heart fields (HF) along the midline of the dorsal pericardial wall. During HF merging, the initially linear heart tube elongates and becomes deformed into a helical tube. This deformation is named cardiac looping. It is the first manifestation of visceral asymmetries and is controlled by molecular signals conferring left or right (LR) identities to the two body halves. Defects in LR-specification (isomerisms) frequently lead to AVC septation defects indicating that LR-specification plays an important role in AVC development. Fate-mapping has shown that, in the post-looping heart, the ventral wall of the AVC, which harbors the superior AV-cushion, derives from the left HF, while the dorsal wall of the AVC, which harbors the inferior AV-cushion, derives from the right HF. The process leading to this situation is unknown. Positional changes of the AVC were documented in the looping embryonic chick heart (HH-stages 11-24) by 3D-OCT + SEM. The original left and right halves of the AVC retain their initial LR-orientation during the first phase of cardiac looping (C-looping, HH-stages 11-13), which is characterized by ventral bending and rightward torsion of the future ventricles. Concomitantly with the subsequent caudal displacement of the ventricles (early S- looping, HH-stages 14-18), the AVC undergoes a torsion, which brings its original left and right halves into their final ventral and dorsal positions, respectively. C-looping defines the direction of future AVC torsion, while AVC torsion itself is caused by early S-looping.
Keywords: Cardiac looping; AVC development; LR-specification