Histology and Immunohistochemistry of the Cardiac Ventricular Structure in the Green Turtle (Chelonia mydas)

The myoarchitecture of the vertebrate cardiac ventricles: evolution and classification

The ventricle of the vertebrate heart is the main segment of the cardiac outflow region. Compared with other cardiac components, it shows remarkable histomorphological variation among different animal groups. This variation is especially apparent in the myocardium, which is generally classified into three main types: trabeculated, compact and mixed. The trabeculated or 'spongy' myocardium is characterized by the existence of trabeculae and deep recesses or intertrabecular spaces, lined by the endocardium. The compact type is composed of condensed myocardial fibers, with almost no trabeculated layer. The mixed type consists of an outer compact layer and an inner trabeculated layer. Among vertebrates, fishes show a great diversity of myocardial types. On this basis, the ventricular myoarchitecture has been categorized into four groups of varying complexity. This classification is made according to (i) the proportion of the two types of myocardium, trabeculated versus compact, and (ii) the vascularization of the heart wall. Here, we review the morphogenetic mechanisms that give rise to the different ventricular myoarchitecture in gnathostomes (i.e. jawed vertebrates) with special emphasis on the diversity of the ventricular myocardium throughout the phylogeny of ancient actinopterygians and teleosts. Finally, we propose that the classification of the ventricular myoarchitecture should be reconsidered, given that the degrees of myocardial compactness on which the current classification system is based do not constitute discrete states, but an anatomical continuum.

Nexilin in cardiomyopathy: unveiling its diverse roles with special focus on endocardial fibroelastosis

Cardiac disorders exhibit considerable heterogeneity, and understanding their genetic foundations is crucial for their diagnosis and treatment. Recent genetic analyses involving a growing number of participants have uncovered novel mutations within both coding and non-coding regions of DNA, contributing to the onset of cardiac conditions. The NEXN gene, encoding the Nexilin protein, an actin filament-binding protein, is integral to normal cardiac function. Mutations in this gene have been linked to cardiomyopathies, cardiovascular disorders, and sudden deaths. Heterozygous or homozygous variants of the NEXN gene are associated with the development of endocardial fibroelastosis (EFE), a rare cardiac condition characterized by excessive collagen and elastin deposition in the left ventricular endocardium predominantly affecting infants and young children. EFE occurs both primary and secondary to other conditions and often leads to unfavorable prognoses and outcomes. This review explores the role of NEXN genetic variants in cardiovascular disorders, particularly EFE, revealing that functional mutations are not clustered in a specific domain of Nexilin based on the cardiac disorder phenotype. Our review underscores the importance of understanding genetic mutations for the diagnosis and treatment of cardiac conditions.

Heart morphology during the embryonic development of Podocnemis unifilis Trosquel 1948 (Testudines: Podocnemididae)

Cardiogenesis is similar in all vertebrates, but differences in the valvuloseptal morphogenesis among non-crocodilian reptiles, birds, and mammals are noted. The origin of mesenchymal structures such as valves that regulate the passage of blood and the formation of partial septa that prevent the complete mixing of oxygen-rich and low-oxygen blood present in adult chelonians are essential in the evolutionary understanding of complete septation, endothermy and malformations, even in mammals. In this context, this study analyzed the heart morphogenesis of Podocnemis unifilis (Testudines: Podocnemididae) from the 4th to the 60th day of incubation. We identified the tubular heart stage, folding of the cardiac tube and expansion of the atrial and ventricular compartments followed by atrial septation by the septum primum, ventricle septation by partial septa, outflow tract septation and the formation of bicuspid valves with cartilage differentiation at the base. The formation of the first atrial septum with the mesenchymal cap is noted during the development of the atrial septum, joining the atrioventricular cushion on the 17th day and completely dividing the atria. Small secondary perforations appeared in the mid-cranial part, observed up to the 45th day. Partial ventricle septation into the pulmonary, venous, and arterial subcompartments takes place by trabeculae carneae thickening and grouping on the 15th day. The outflow tract forms the aorticopulmonary and interaortic septa on the 16th day and the bicuspid valves, on the 20th day. Therefore, after the first 20 days, the heart exhibits a general anatomical conformation similar to that of adult turtles.

Ventricular Septation and Outflow Tract Development in Crocodilians Result in Two Aortas with Bicuspid Semilunar Valves

Background: The outflow tract of crocodilians resembles that of birds and mammals as ventricular septation is complete. The arterial anatomy, however, presents with a pulmonary trunk originating from the right ventricular cavum, and two aortas originating from either the right or left ventricular cavity. Mixing of blood in crocodilians cannot occur at the ventricular level as in other reptiles but instead takes place at the aortic root level by a shunt, the foramen of Panizza, the opening of which is guarded by two facing semilunar leaflets of both bicuspid aortic valves. Methods: Developmental stages of Alligator mississipiensis, Crocodilus niloticus and Caiman latirostris were studied histologically. Results and Conclusions: The outflow tract septation complex can be divided into two components. The aorto-pulmonary septum divides the pulmonary trunk from both aortas, whereas the interaortic septum divides the systemic from the visceral aorta. Neural crest cells are most likely involved in the formation of both components. Remodeling of the endocardial cushions and both septa results in the formation of bicuspid valves in all three arterial trunks. The foramen of Panizza originates intracardially as a channel in the septal endocardial cushion.

Endocardial fibroelastosis and dilated cardiomyopathy - the past and future of the interface between histology and genetics

Endocardial fibroelastosis (EFE) signifies the pathological process by which collagen and elastin are focally or diffuse deposited in the endocardium of the left ventricle. The new layer causes left ventricular dysfunction sometimes with fulminant progression to heart failure. EFE is a major component in many congenital heart abnormalities but can also occur in the absence of heart malformations, either as a primary process or in response to cardiac injury. The endothelial-mesenchymal transition (EndMT) abnormalities seem to be main pathogenic factor in fibroelastosis development. The "gold standard" for diagnosis of primary EFE (pEFE) is the histological examination. Additionally, genetic studies may help to establish the natural course of the disease and to communicate prophylactic measures to family members of the affected child. Moreover, in the newborn, EFE takes the form of dilated cardiomyopathy (DCM) with unfavorable evolution. The proper management should be established considering negative prognostic factors, involving early transplantation, drug therapy and long-term follow-up.