The development of the sturgeon heart

Abstract

This paper presents a sequential analysis of the development of the sturgeon (Acipenser naccarii) heart from the end of gastrulation to the early juvenile stages. At late neurulation, the heart appears as a straight, short tube located over the endoderm that forms the wall of the yolk sac, in front of the developing head. The heart axis is aligned with the axis of the developing head. Subsequently, the heart elongates and adopts a C-shape, and its axis becomes perpendicular to that of the head. Around the time of hatching, the heart loses the loop and appears as a mostly straight tube with the chambers arranged in a craniocaudal sequence: outflow tract, ventricle, atrium, and a small sinus venosus. During the first 4 days post-hatching (dph), the heart starts looping again, adopts a C-shape, and undergoes a counterclockwise movement that brings the atrium to the left of the outflow tract and the ventricle to a caudal position. Thus, a primary and a secondary cardiac loop occur in the sturgeon. Later, the atria come to occupy a middle position behind the outflow tract, and the sinus venosus shifts from a caudal to a dorsal position. A morphological arrangement similar to that found in adult sturgeons is attained in all specimens at days 7-9 dph. The external changes are accompanied by a series of internal modifications that include trabeculation (3-4 dph), development of endocardial cushions in the atrioventricular canal (4 dph) and in the conus arteriosus (3-4 dph), conus (22-24 dph) and atrioventricular (18-20 dph) valve formation, and development of the epicardium (4 dph) and the coronary vessels (10 dph). The main developmental features of the heart have been registered, and a basic body of information, which should be very useful in future developmental studies, has been established. Similarities and dissimilarities between the development of the sturgeon heart and that of other vertebrates are underscored.

Absence of heartbeat in the Xenopus tropicalis mutation muzak is caused by a nonsense mutation in cardiac myosin myh6

“…The ancestral teleost genome duplication has also led to wholesale reassignment and shuffling of gene functions (Force et al, 1999; Postlethwait et al, 2000), complicating orthology assignment and contributing to the diversity of developmental mechanisms. For example, zebrafish cardiac valves are thought to form by an atypical direct invagination of endocardial epithelia into leaflet structures (Scherz et al, 2008) rather than via a mesenchymal ‘endocardial cushion’ intermediate as has been described in other vertebrates (Armstrong and Bischoff, 2004; Eisenberg and Markwald, 1995) and indeed other fish (Gallego et al, 1997; Icardo et al, 2004). Genetic analysis of X. tropicalis , with its more conventionally-organized tetrapod genome and array of functional assays, will help bridge studies of cardiac development from teleost models to amniotes.…”

Morphological analysis of the hagfish heart. I. The ventricle, the arterial connection and the ventral aorta

“…Specifically, the atrium ascends from a caudal position in relation to the ventricle to occupy a position dorsal and cranial to it. This occurs in tetrapods (see Icardo et al, ) as well as in the fish species examined (for instance, see Stainier et al, ; Icardo et al, ) and depends on the progressive incorporation of cardiac precursors to the growing heart. It follows that if chamber incorporation and/or molecular differentiation are defective, looping would be aborted or remains incomplete.…”

High-speed imaging of developing heart valves reveals interplay of morphogenesis and function

“…One possible explanation is that this invagination is the more basal mechanism for valve development, with large mesenchymal cushions arising in tetrapods due to the demands of the more complicated, septated hearts of higher vertebrates. However, this explanation does not seem to hold true, as histological analyses of the hearts of both the dogfish (Gallego et al, 1997), a chondrichthyan, and the sturgeon (Icardo et al, 2004), a more basal fish than zebrafish, show mesenchymal cushions, suggesting that the mechanism of forming mesenchymal cushions by EMT is more ancient than simple invagination. An alternative explanation is that invagination is a novel mechanism that evolved at some point in the zebrafish lineage since its divergence from sturgeon.…”