Functional Morphology of the Cardiac Jelly in the Tubular Heart of Vertebrate Embryos

Abstract

The early embryonic heart is a multi-layered tube consisting of (1) an outer myocardial tube; (2) an inner endocardial tube; and (3) an extracellular matrix layer interposed between the myocardium and endocardium, called “cardiac jelly” (CJ). During the past decades, research on CJ has mainly focused on its molecular and cellular biological aspects. This review focuses on the morphological and biomechanical aspects of CJ. Special attention is given to (1) the spatial distribution and fiber architecture of CJ; (2) the morphological dynamics of CJ during the cardiac cycle; and (3) the removal/remodeling of CJ during advanced heart looping stages, which leads to the formation of ventricular trabeculations and endocardial cushions. CJ acts as a hydraulic skeleton, displaying striking structural and functional similarities with the mesoglea of jellyfish. CJ not only represents a filler substance, facilitating end-systolic occlusion of the embryonic heart lumen. Its elastic components antagonize the systolic deformations of the heart wall and thereby power the refilling phase of the ventricular tube. Non-uniform spatial distribution of CJ generates non-circular cross sections of the opened endocardial tube (initially elliptic, later deltoid), which seem to be advantageous for valveless pumping. Endocardial cushions/ridges are cellularized remnants of non-removed CJ.

Human heart-forming organoids recapitulate early heart and foregut development

“…However, in the embryo, the FHF forms adjacent to the AFE, whereas SHF cells appear medially to the FHF 46 . Last, formation of cardiac jelly, which develops around week 4 of human gestation between the myocardium and endocardium 47 , was not apparent in HFOs, potentially reflecting the early developmental stage. Despite these differences from spatiotemporal heart and foregut development in vivo, our HFO approach mimics important aspects of native pattern formation.…”

Decellularized Human Dermal Matrix as a Biological Scaffold for Cardiac Repair and Regeneration

“…Cardiac jelly is the primitive cardiac ECM that mechanically connects the inner endocardial layer and the outer myocardium layer of the tubular heart and that forms a thick viscoelastic layer that mechanically supports the valveless pumping function of the embryonic heart (Garita et al, 2011). GAGs control the hydration of the cardiac jelly generating turgor pressure that is involved in the remodeling process of the ventricular tube that initiates trabeculation and formation of cardiac chambers (Farouz et al, 2015;Männer and Yelbuz, 2019). Further important components of d-HuSk that are also crucial components of the cardiac matrix, since its earliest form as cardiac jelly, include the non-collagenous glycoproteins fibronectin and laminin.…”

Bearing My Heart: The Role of Extracellular Matrix on Cardiac Development, Homeostasis, and Injury Response

“…At E8.0, the heart has a tubular shape and is composed of two cell layers—the myocardium (outer layer) and the endocardium (inner layer)—separated by an amorphous matrix-denominated cardiac jelly ( Figure 1 , heart tube). The cardiac jelly consists of a network of ECM molecules enriched in HA; collagens I, III, and IV; laminin; FN; fibrillin; perlecan; fibulin-1; and thrombospondin (TSP) ( Little and Rongish, 1995 ; Männer and Yelbuz, 2019 ). The heart expands by the contribution of second heart field (SHF) cells and undergoes a series of looping events at E8.5 ( Figure 1 , looping heart).…”