Dennis E. Morse

Distribution of the neural cell adhesion molecule (NCAM) during heart development

The neural cell adhesion molecule, NCAM, was localized in the embryonic chick heart from Hamburger-Hamilton stage 14 up to hatching and in the adult heart. A monoclonal antibody directed to NCAM was used with the indirect antibody technique to stain frozen sections with immunoperoxidase. The myocardium showed immunoreactivity at stages 15 and 21, with little to no staining of epicardium, endocardium or atrioventricular endocardial cushion tissue. At stage 22, additional immunoreactivity was found in the endocardium of both the atrial septum and the atrial and ventricular surfaces of the atrioventricular cushions. Endocardial-derived mesenchymal cells within the cushions were also immunostained for NCAM. A gradient of NCAM staining was evident in the ventricular wall by stage 16. The staining intensity in the myocardium subjacent to the epicardium was less than found near the ventricular lumen. Biochemical analyses revealed that the embryonic heart expresses polysialylated NCAM. Upon desialylation with the endoneuraminidase Endo-N, the predominant heart NCAM has an apparent molecular weight of 155 to 160 kDa, which is distinct in size from the predominant forms found in embryonic chick nervous system (180, 140 and 120 kDa). NCAM expression is regionally regulated in the heart. The pattern of its expression is consistent with our hypothesis that it is involved in (1) differentiation of the atrial and ventricular walls, (2) fusion of the atrial septum with the endocardial cushions, (3) fusion of the endocardial cushions, and (4) formation and remodeling of ventricular trabeculae.

Insulin immunoreactivity in the fetal and neonatal rat retina

The ganglion cell layer of pre- and postnatal rat retina is positive for insulin immunoreactivity. At birth the inner nuclear layer also stains for insulin. By 5 days after birth the layers characteristic of the mature retina are demonstrable. At this time the outer nuclear layer and both limiting membranes show insulin reactivity. The lens is positive for insulin at all stages studied and the retinal pigment and choroid layers are positive after birth. These observations suggest that insulin may be important in differentiation and/or maturation of the retina.

SCANNING ELECTRON MICROSCOPY OF EMBRYONIC FUSION PROCESSES

Publisher Summary Organogenesis involves a synchronized series of morphological and biochemical alterations and transformations to convert an organ anlage into its adult form. A partial list of these changes includes cell migration, proliferation, differentiation and death, extracellular matrix modifications, and epithelial-mesenchymal interaction. Fusion of epithelium-covered surfaces in organogenesis to create tubes, chambers, septa, partitions, and processes demonstrates many of the changes. Scanning electron microscopy (SEM) provides a method for examination of morphological alterations that occur before and during fusion of epithelia. Classification of the types of epithelial fusion is accomplished by referring to the embryonic germ layers of origin for the epithelia involved. Fusion of epithelia derived from ectoderm can be subdivided into two categories; that from surface ectoderm and that from neuroectoderm. Surface ectodermal fusion is represented in developing mammalian face and palate. Neural tube formation and optic fissure closure are in the neuroectoderm category.

Renal Corpuscle Development in the Dog

Renal vesicle formation and glomerular development were studied in the 44-day dog fetus with the use of the scanning electron microscope. In the early stages of glomerular development the luminal aspect of the columnar glomerular epithelium shows a cobblestone appearance with sparse microvilli and occasional cilia. Marginal club-shaped processes are the earliest sign of prodocyte process development. These interdigitate with neighboring cell processes and elongate before developing definitve foot processes. Glomerular epithelial differentiation is uneven and multifocal, but once started, proceeds rapidly. The capsular epithelium progresses from cuboidal (in the vesicular stages) to squamous (in the mature glomerulus) with the area adjacent to the proximal convoluted tubule being the last area to differentiate fully.