Francis J. Manasek

An indirect immunofluorescence study of the distribution of fibronectin during the formation of the cushion tissue mesenchyme in the embryonic heart

Indirect immunofluorescence studies have localized fibronectin (FN) within the trunco-conal ridges of the chick embryo heart during the formation of the cushion tissue mesenchyme. Prior to cell migration into the endocardial pads, fluorescence for FN is demonstrated almost entirely in association with the basal surfaces of endocardium and myocardium. Scattered spots and thin dotted-strands of fluorescent material can be demonstrated in the cardiac jelly. Cushion tissue (CT) cells migrating into the cardiac jelly have patches of fluorescent material associated with their surfaces. Filopodial processes always show intense fluorescence. The close association between the fluorescence and the surface of the CT cells suggests that FN may be implicated in the interaction of these cells with the matrical components of the cardiac jelly and, therefore, in the process of cell migration into the endocardial pads. The intensity and amount of FN staining decreased concomitantly with the progressive accumulation of cells in the cushion areas. After the completion of CT cell migration only reduced amounts of faint fluorescence remained in the endocardial pad areas. The possible significance of the changes observed in the distribution of FN during the formation of the cushion tissue mesenchyme is discussed.

Glycoprotein synthesis and tissue interactions during establishment of the functional embryonic chick heart.

Abstract Embryonic hearts were shown to synthesize fucose containing glycoprotein before, during and after differentiation. These glycoproteins are associated with cells as well as being part of the extracellular matrix. Basal laminae are labelled heavily indicating synthesis and elaboration of lamina glycoprotein. Precardiac splanchnic mesoderm was shown to make contact with newly synthesized endodermal glycoprotein. Based on the demonstration and regional localization of embryonic glycoproteins, a model of cardiac myogenesis is proposed. Basic to this model is the proposition that cell recognition of matrix is a specific function of the glycoproteins that are present in it.

Fibronectin distribution during early chick embryo heart development

The distribution of fibronectin (FN) during early stages of chick embryo heart development has been studied by indirect immunofluorescence methods. The cardiac extracellular matrix (cardiac jelly) was almost devoid of FN-positive material throughout the period studied (stages 8-18). Intensely extracellular fluorescent material was only demonstrated at the heart midline and in the dorsal mesocardium. Fluorescence associated with the basal surface of the myocardium was demonstrated first at the time of fusion of the two heart tubes. While the heart remains attached to the embryonic trunk by the dorsal mesocardium, two different myocardial basal zones can be distinguished according to the intensity of fluorescence: an intensely stained dorsal zone and a much less fluorescent ventral zone. The endocardium did not present a strongly fluorescent basement membrane until stage 13. The intensity of fluorescence of the endocardial basal surface varied according to the rostrocaudal levels of the heart and also to the development stage of the embryo. The levels of fluorescence increased in myocardium and endocardium at the onset of trabeculation but decreased as trabeculation was completed. The quantitative and qualitative variations of FN distribution have been associated with a number of developmental events.

Structural glycoproteins of the embryonic cardiac extracellular matrix

Fucose containing structural glycoproteins of early embryonic chick hearts were shown to be only slightly solubilized (30% recovery) by LiCl, urea, ammonium acetate, SDS or reduction with dithiothreitol and alkylation with iodoacetamide. Solubilization is essentially complete (90% recovery) if reduction and alkylation takes place in the presence of SDS or if native material is digested with testicular hyaluronidase. These data suggest that newly synthesized embryonic cardiac structural glycoproteins become incorporated into the matrix complex with other components both covalently and non-covalently. By electrophoretic criteria there are seemingly relatively few molecular species of glycoproteins composed of glycopeptides that can be divided into four major groups on the basis of charge. Because of the interactions between matrix macromolecules the properties, hence biological function, may change as a result of changes in interactions as well as composition.