Sulfated extracellular matrix production in the embryonic heart and adjacent tissues
01 Aug 1970-Journal of Experimental Zoology (Wiley Subscription Services, Inc., A Wiley Company)-Vol. 174, Iss: 4, pp 415-439
TL;DR: The results show that the production of sulfated extracellular matrix is not restricted to chondrogenic tissues in very young embryos, but that this function becomes selectively repressed as the embryo matures, and suggests that Embryonic cardiac muscle is a secretory as well as contractile tissue and the two “specialized” functions are not mutually exclusive.
Abstract: The incorporation of S35-sulfate into tissues and extracellular matrix of chick embryos ranging in age from stage 8 (4 somites) to stage 12 (16 somites) was examined. 0.05 mc S35 were added to embryos grown in vitro and after appropriate incubation periods the embryos were fixed and embedded in plastic. Radio-autographs of 1 μ plastic sections of embryos between stages 8 and 9 (4 to 9 somites) showed heavy S35 incorporation by all tissues, especially the notochord, neural fold and precardia. Between stages 10 (10 somites) and 12 (16 somites) the incorporation of S35 decreases in all tissues examined except the myocardium.
These results show that the production of sulfated extracellular matrix is not restricted to chondrogenic tissues in very young embryos, but that this function becomes selectively repressed as the embryo matures. This suggests that S35 incorporation during cartilage production by chondrogenic tissues (such as notochord) in older embryos involves the re-expression of an earlier embryonic trait, rather than the acquisition of a wholly new capability.
The myocardium, on the other hand, continues to secrete a sulfated matrix even after the cells contain well developed myofibrils and become functional myocytes. Embryonic cardiac muscle is therefore a secretory as well as contractile tissue and the two “specialized” functions are not mutually exclusive.
Citations
More filters
TL;DR: The study established loci in developing cushions where disruption where disruption of the developmental sequence could engender valvular or septal defects.
Abstract: Development of chick and rat endocardial cushions (cardiac mesenchyme) was studied histologically (using Nomarski differential interference optics on living and unfixed tissue), ultrastructurally (scanning and transmission electron microscopy), cytochemically (using acidified dialyzed iron as a visual probe for polyanionic material) and autoradiographically (using 35S) to elucidate the origin of the mesenchyme, the morphologic sequences leading to cushion formation and secretion of sulfated glycosaminoglycans, if any, by migrating mesenchymal cells. Cushion formation was similar for both species. Mesenchymal cells appeared initially, in 16- to 18-somite embryos, beneath the endothelium (which lacked a basal lamina) of the future atrioventricular canal and outflow tract. The cytoplasm of cushion mesenchymal cells was structurally similar to the ensothelium; probably these cells arose by proliferation of the endothelium. Mitotic figures among the "seeded" cells were also numerous. Cushion cells were initially attached to the endothelium by desmosomes but acquired motile apparatus (pseudopodia and filopodia containing microtubules and microfilamentous bundles). Serial sectioning of successively-aged embryos (20-44 somites) indicated a centrifugal migratory direction. Interaction of the cell processes with extracellular matrix suggested that the latter was used as a migratory substrate. Contact of the advancing wedge of cushion cells with the myocardium produced no alteration in cell structure or mitotic activity. Localization of hyaluronidase-sensitive, dialyzed iron (DI) precipitates in 250-nm Golgi vacuoles and hyaluronidase-sensitive 35S-endangendered silver grains over cushion cells indicated that this tissue contributed sulfated macromolecules to the matrix. Localization of hyaluronidase-labile, DI material in coated, endocytic-like vesicles and caveolae also suggested potential modification or conditioning of the matrix by migrating mesenchymal cells. Altogether, the study established loci in developing cushions where disruption where disruption of the developmental sequence could engender valvular or septal defects.
436 citations
TL;DR: Cardiac morphogenesis as it relates to heart valve formation is reviewed and selected growth factors, intracellular signaling mediators, and extracellular matrix components involved in the creation and remodeling of endocardial cushions into mature cardiac structures are highlighted.
Abstract: The valves of the heart develop in the embryo from precursor structures called endocardial cushions. After cardiac looping, endocardial cushion swellings form and become populated by valve precursor cells formed by an epithelial-mesenchymal transition (EMT). Endocardial cushions subsequently undergo directed growth and remodeling to form the valvular structures and the membranous septa of the mature heart. The developmental processes that mediate cushion formation include many prototypic cellular actions including adhesion, signaling, migration, secretion, replication, differentiation, and apoptosis. Cushion morphogenesis is unique in that these cellular possesses occur in a functioning organ where the cushions act as valves even while developing into definitive valvular structures. Cardiovascular defects are the most common congenital defects, and one of the most common causes of death during infancy. Thus, there is significant interest in understanding the mechanisms that underlie this complex developmental process. In this regard, substantial progress has been made by incorporating an understanding of cardiac morphology and cell biology with the rapidly expanding repertoire of molecular mechanisms gained through human genetics and research using animal models. This article reviews cardiac morphogenesis as it relates to heart valve formation and highlights selected growth factors, intracellular signaling mediators, and extracellular matrix components involved in the creation and remodeling of endocardial cushions into mature cardiac structures.
345 citations
TL;DR: The chapter describes the complicated proliferative behavior of cardiac-muscle cells both in normal myogenesis and regeneration and its dependence on the differentiative properties of these cells.
Abstract: Publisher Summary This chapter discusses the interrelations of the proliferation and differentiation processes during cardiac myogenesis and regeneration. Myogenesis has attracted the ever-increasing interest of investigators for more than 100 years. Interrelationships between cytodifferentiation and the proliferation of myogenic cells have been found to be highly complicated and apparently not identical in diverse types of myogeneses. Some investigators believe that myocardial cells possess an intrinsic capacity to dedifferentiate and multiply at the borders of necroses which, however, is not manifested overtly because of the lack of permissive conditions and appropriate stimuli or, possibly, because of nonmuscle cell overgrowth. The chapter describes the complicated proliferative behavior of cardiac-muscle cells both in normal myogenesis and regeneration and its dependence on the differentiative properties of these cells.
307 citations
TL;DR: The results obtained by autoradiography and biochemical analysis of labeled macromolecules selectively extracted from this cell-free space suggest that hyaluronic acid is a major component.
302 citations
TL;DR: Results indicated that both endocardial surface and internal features could be related to developmental changes in microenvironment and function.
254 citations
References
More filters
TL;DR: The preparation of a series of normal stages of the chick embryo does not need justification at a time when chick ernbryos are not only widely used in descriptive and experimental embryology but are proving to be increasingly valuable in medical research, as in work on viruses and cancer.
Abstract: FORTY-FIVE FIGURES The preparation of a series of normal stages of the chick embryo does not need justification at a time when chick ernbryos are not only widely used in descriptive and experimental embryology but are proving to be increasingly valuable in medical research, as in work on viruses and cancer. The present series was planned in connection with the preparation of a new edition of Lillie’s DeueZopmerzt of the Chick by the junior author. It is being published separately to make it accessible immediately to a large group of workers. Ever since Aristotle “discovered” the chick embryo as the ideal, object for embryological studies, the embryos have been described in terms of the length of time of incubation, and this arbitrary method is still in general use, except for the first three days of incubation during which more detailed characteristics such as the numbers of somites are applied. The shortcomings of a classification based on chronological age are obvious to every worker in this field, for enormous variations may occur in embryos even though all eggs in a setting are plmaced in the incubator at the same time. Many factors are responsible for the lack of correlation between chronological and structural age. Among these are : genetic differences in the rate of development of different breccls (eg., the embryo of the White Leghorn breed develops more 49
12,079 citations
Journal Article•
8,559 citations
Journal Article•
5,201 citations
TL;DR: Embryonic chick myocardium (stages 8+ to 12−) was studied by light and electron microscopy and the amount of granular reticulum contained in the myocardial cell cytoplasm is large and suggests that these cells may have a secretory function.
Abstract: Embryonic chick myocardium (stages 8+ to 12−) was studied by light and electron microscopy. The myocardium, which is initially comprised of radially oriented cells with large intercellular spaces gradually becomes more tightly packed. Intercellular spaces decrease and the cells assume a circumferential orientation. Myocardial cells remain epithelial throughout formation of the functional tubular heart and specialized epithelial junctions (apical junctional complex or terminal bars) undergo modification to form intercalated discs. Embryonic myocardial cells contain large amounts of free ribosomes and particulate glycogen, the latter often associated with portions of granular reticulum. Unlike developing skeletal muscle. The amount of granular reticulum contained in the myocardial cell cytoplasm is large and, along with a hypertrophied Golgi apparatus, suggests that these cells may have a secretory function. These organelles persist during the initial period of fibril formation. Myofibrils apparently form from non filamentous precursor material and not by alignment of sequentially synthesized components.
337 citations
TL;DR: The ultrastructure of the developing chick ventricular myocardium was examined between Hamburger-Hamilton stage 12 − (15 somites; about 45 hours incubation) and the time of hatching (about 21 days incubation).
Abstract: The ultrastructure of the developing chick ventricular myocardium was examined between Hamburger-Hamilton stage 12 − (15 somites; about 45 hours incubation) and the time of hatching (about 21 days incubation). The myocardium is an epithelial tissue initially containing only developing myocytes. No epicardium is present and no mesenchymal cells such as fibroblasts are seen. By the third day of development, portions of the ventricular endocardium invade the myocardium. After this event and the development of the epicardium from an extramyocardial source, mesenchymal cells are seen within the myocardium. These cells, the first nonmuscular components seen within the myocardium, are probably fibroblasts derived from the endocardium or the epicardium. The myocardium is honeycombed with large anastomosing channels. The extracellular matrix within these spaces is electron-lucent until the nonmyocardial mesenchymal cells appear. A flocculent component then develops. Early cardiac myocytes contain few fibrils and large amounts of cytoplasm. The fibrils are not regularly oriented within the young cells. As development proceeds, more fibrils are formed; the cytoplasm decreases and the fibrils become aligned in the mature orderly pattern. Possible mechanisms to explain these phenomena are discussed.
224 citations