N-cadherin relocalization during cardiac trabeculation

Abstract

During cardiac trabeculation, cardiomyocytes delaminate from the outermost (compact) layer to form complex muscular structures known as trabeculae. As these cardiomyocytes delaminate, the remodeling of adhesion junctions must be tightly coordinated so cells can extrude from the compact layer while remaining in tight contact with their neighbors. In this study, we examined the distribution of N-cadherin (Cdh2) during cardiac trabeculation in zebrafish. By analyzing the localization of a Cdh2-EGFP fusion protein expressed under the control of the zebrafish cdh2 promoter, we initially observed Cdh2-EGFP expression along the lateral sides of embryonic cardiomyocytes, in an evenly distributed pattern, and with the occasional appearance of punctae. Within a few hours, Cdh2-EGFP distribution on the lateral sides of cardiomyocytes evolves into a clear punctate pattern as Cdh2-EGFP molecules outside the punctae cluster to increase the size of these aggregates. In addition, Cdh2-EGFP molecules also appear on the basal side of cardiomyocytes that remain in the compact layer. Delaminating cardiomyocytes accumulate Cdh2-EGFP on the surface facing the basal side of compact layer cardiomyocytes, thereby allowing tight adhesion between these layers. Importantly, we find that blood flow/cardiac contractility is required for the transition from an even distribution of Cdh2-EGFP to the formation of punctae. Furthermore, using time-lapse imaging of beating hearts in conjunction with a Cdh2 tandem fluorescent protein timer transgenic line, we observed that Cdh2-EGFP molecules appear to move from the lateral to the basal side of cardiomyocytes along the cell membrane, and that Erb-b2 receptor tyrosine kinase 2 (Erbb2) function is required for this relocalization.T o maximize its function, the heart undergoes a series of morphological changes during development, with trabeculation being one of the main processes (1-5). Trabeculae initially appear as myocardial ridges in the outer curvature of the ventricle, and they are important for cardiac function, as evidenced by studies of hypo-and hypertrabeculation models (3,(6)(7)(8)(9)(10)(11). Previous studies have shown that Erbb2 signaling is essential for trabeculation (3,6,7,10,11). Moreover, disturbing blood flow or cardiac contractility in the ventricle perturbs trabeculation (4, 12, 13), suggesting an important role for mechanical forces in this process. Our understanding of the cellular mechanisms regulating trabeculation remains fairly limited. Cardiomyocytes in the early heart tube show an epithelium-like morphology (3,14). During trabeculation, some cardiomyocytes delaminate and enter the trabecular layer, where they join other trabecular cardiomyocytes to form ridge-like structures (3,15). Previous studies have shown that the most proximal cardiomyocytes in the trabecular layer remain tightly attached to the basal side of compact layer cardiomyocytes (3, 15). Some of the key molecules involved in cellcell adhesion belong to the cadherin family, and they also play crucial roles in...

The Hippo pathway effector Wwtr1 regulates cardiac wall maturation in zebrafish

“…In 52 hpf wild-type hearts, N-cadherin-GFP is localized at the junctions between cardiomyocytes (Cherian et al, 2016); in wwtr1 −/− hearts, it appeared to distribute in a punctate manner over the apical and basal surfaces of some cardiomyocytes (Fig. 5D).…”

The transmembrane protein Crb2a regulates cardiomyocyte apicobasal polarity and adhesion in zebrafish

“…Moreover, during tissue morphogenesis, mechanical tension plays a key role in controlling actomyosin networks and cell-cell junction remodeling to maintain cell shape (Lecuit et al, 2011;Lecuit and Yap, 2015). Compact layer CMs are subjected to mechanical forces necessary for ventricular chamber maturation (Cherian et al, 2016). In view of these data, we propose that loss of cell-cell adhesions in crb2a mutant hearts is at least partially responsible for the CM multilayering phenotype coming from the collapse of the CM monolayer prior to the onset of delamination.…”

“…Cardiac trabeculation in zebrafish has been proposed as an EMTlike process whereby a subset of CMs undergo apical constriction and lose apicobasal polarity as they delaminate to seed the trabecular layer (Liu et al, 2010;Staudt et al, 2014;Cherian et al, 2016;Jiménez-Amilburu et al, 2016). However, it remains unclear how CM apicobasal polarity is regulated.…”

Defects in Trabecular Development Contribute to Left Ventricular Noncompaction

“…Trabeculation depends on tissue mechanics, cardiac jelly composition, cell behavior, and cell-to-cell signaling between the endocardium and the myocardium [12][13][14]. In mammals, both oriented cell division and delamination of cardiomyocytes from the early myocardial layer are important early events in the formation of trabeculae.…”