Endocardial cells combine to form endocardium tissues and are the inner-most layer of tissues that line the chambers of the heart. These tissues play a role in controlling myocardial contractions in mammals.
Endocardial notch signaling is one of several forms of communication utilized by endocardial cells to communicate with each other. It is a highly conserved cell signaling system meaning that the both the nucleic acid and protein sequences are similar and in some cases are even identical in different species of organisms.
There are four different notch receptors: NOTCH 1, NOTCH 2, NOTCH 3, and NOTCH 4. The notch signaling system also includes notch ligands that act as the receptors. These ligands are transmembrane receptor proteins that span the length of the membrane of the endocardial cell. The notch signaling receptor is a heterodimer transmembrane protein, meaning that the protein was formed from the combination of two normally non-covalently bonded macromolecules.
Notch signaling is activated by cell to cell contact causing the ligand to bind to the notch receptor. When this signal is activated it leads to three cleavages. The first cleavage is activated by an enzyme known as TACE/ADAM17 and this is responsible for the cleavage of the membrane. The other two cleavages are controlled by a mixture of enzyme (presenilin1, presenilin2, Pen-2, Aph-1, and nicastrin).
This form of signaling allows a group of cells to arrange themselves to form a large structure by influencing them to switch off certain traits in neighbouring cells.
Cell adhesion also occurs in endocardial cells.
The endocardial cell is structural made of 5-6 cubular cells along the AP axis of the endocardiaum (Westerfield et al 2009). The endocardial cell migrate mid-line before myocardial cells. Preceding myocardial cell bilateral migration, localized cardiomycytes change direction. This causes myocardial cells to alter direction and move inward to meet the endocardial cells thus establishing nascent heart circumference. Bilateral heart fields are formed as a result of fusion at the midline between the two forming cardiac tissue discs, which are located at the central circumference of the future ventricle (Bakkers 2011).
The physical proximity of the endocardial and myocardial cell suggests that the two may be influenced by each other or that they both respond to the similar environmental cues during their migration towards the midline. One such non-cardiac tissue to which both myocardial and endocardial cells are enar is the endoderm. The endoderm, which will later form the gut is shown to be an influencing factor in cardiac fusion.
1. Monte Westerfield, Leonard I. Zon, H. William Detrich, III ‘Essential Zebrafish Methods’. 2009.
Monte Westerfield, Leonard I. Zon, H. William Detrich, III ‘Essential Zebrafish Methods’. 2009.
Jeroen Bakkers. ‘Zebrafish as a model to study cardiac development and human cardiac disease
Received January 18, 2011.
Revision received March 22, 2011.
Accepted April 1, 2011