Expression of Sox8, Sox9 and Sox10 in the developing valves and autonomic nerves of the embryonic heart.

We describe the expression pattern of Sox8, Sox9 and Sox10 during the development of the chick embryo heart. These Sox genes constitute the group E of the large Sox family of transcription factors. We show that the expression of Sox8, Sox9 and Sox10 in the developing heart correlates with heart septation and with the differentiation of the connective tissue of the valve leaflets. Sox10 appears also as a specific marker of developing heart nerves. These findings fit with the occurrence of morphological and functional anomalies of the heart reported in humans deficient for Sox9 and Sox10.

Schistosoma mansoni infection in owl monkeys (Aontus nancymai): evidence for the early elimination of adult worms.

Detailed parasitologic, serologic, clinical and histopathologic studies were conducted in owl monkeys (Aotus nancymai) exposed to varying numbers of cercariae of Schistosoma mansoni. All the experimental animals had clinical symptoms suggestive of infection (weight loss diarrhoea, mucus in stools, etc.) which were not seen in uninfected individuals. The only A. vociferans included in this study passed S. mansoni eggs 8 weeks after infection. None of the A. nancymai passed eggs in their faeces. No adult worms were recovered following perfusion of the sacrificed experimental monkeys, suggesting that they were early eliminated. Serological techniques (ELISA-SEA and COPT) allowed diagnosis of infection, starting 9 weeks post challenge, in all but one A. nancymai exposed to 100 cercariae. Granulomas containing eggs were observed predominantly in liver and less extensively in intestine, suggesting that adult worms were mainly lodged in the intrahepatic portal system. We conclude that A. nancymai is susceptible to infection with S. mansoi, with the worms reaching sexual maturity, but being eliminated shortly after oviposition.

Myocardial interatrial septum loses its epithelial organization by mesenchymal influence. Structural and ultrastructural study.

During atrial septation, the septum primum fuses with the atrioventricular endocardial cushions and myocardial-mesenchymal interactions occur. In order to evaluate the cellular events that take place during this particular interaction a structural, ultrastructural and histochemical study was performed. Our findings indicate that from the fourth day of development, the distal myocardium of the interatrial septum, which interacts with mesenchymal tissue, loses its appearance of an epithelial sheet and becomes a loosely organized tissue. The distal myocytes of the interatrial septum which get progressively separated show features of migratory cells, the final localization of which is the mesenchymal tissue of the adjacent endocardial cushions. These tissue changes involve basal membrane disruption, reduction in the number of desmosomes and intercalated discs with the subsequent appearance of large intercellular spaces between myocytes, myofibrillar disarrangement and acquisition by myocytes of a secretory phenotype characterized by numerous cytoplasmic vesicles. These events occur in a similar way in the atrioventricular canal, where a myocardial-mesenchymal interaction also occurs. In both regions the mesenchymal endocardial cushions and its associated extracellular matrix seem to direct the dissociation of the myocardial tissue and the subsequent migratory cellular behaviour of the interacting myocytes. This is an interesting, and little known, example of a cellular phenotypic transformation during cardiac development.

The atrioventricular valves of the mouse. I. A scanning electron microscope study.

This paper reports a scanning electron microscope study of the morphology of the atrioventricular (AV) valves in the mouse. The leaflet tissue of the 2 AV valves consists of a continuous veil that shows no commissures or clefts. In all instances, the chordae that arise from the papillary system merge with the free border of the leaflet tissue. No distinct terminations of chordae were observed on the ventricular face of the valves. The leaflet tissue of the right AV valve can be divided into parietal and septal components on the basis of the insertion into the ventricular wall and of the papillary system. While the septal component is similar in shape, location and tension apparatus to the septal tricuspid leaflet in man, the parietal component appears to correspond to the anterior and posterior human leaflets. This segment of the valve is served by 3 papillary muscles that arise from the septal wall. The right AV valve is not a tricuspid structure from the morphological standpoint, but appears to function as such because of the particular attachment of the papillary muscles. The leaflet tissue of the mitral valve is served by 2 papillary muscles, anterior and posterior, which consist of muscular trabeculae extending from the heart apex to the base of the valve. These muscles remain associated with the ventricular wall. The leaflet tissue attaches directly to these papillary muscles, which give rise to a very small number of slender chordae. There are thus several important differences between the AV valves of the mouse and man.(ABSTRACT TRUNCATED AT 250 WORDS)

Sparganum proliferum: an overview of its structure and ultrastructure.

A detailed study of the structure and ultrastructure of Sparganum proliferum was made possible for the first time thanks to the successful in vitro and in vivo maintenance of this rare parasite. Although S. proliferum exhibits many of the classical tegumental and parenchymal structures previously described for other larval cestodes, these are either arranged in a distinct fashion or, in some cases, may be completely different. Among the latter and of special interest are the single or multiple parenchymal cavities, surrounded by tegument, which in some instances appear to act as a primitive digestive tract.

Origin of mesenchymal tissue in the septum primum: a structural and ultrastructural study.

A structural, ultrastructural and histochemical study in chick embryos indicates that the septum primum mesenchymal tissue originate between 3 and 5 days of development and that their origin may be related to an activation of endocardial cells that cover the septum primum. By day 3, endocardial cells display migratory appendages, cell hypertrophy and an increase in secretory and mitotic activity. In later stages (day 4) hypertrophic endocardial cells undergoing division seem to delaminate and translocate toward the subendocardial space to give rise to free mesenchymal-type cells. These results suggest that the endocardium makes up the bulk of the septum primum mesenchymal tissue as has been demonstrated during mesenchymal tissue formation in the atrioventricular canal and outflow tract. Before and during mesenchymal tissue formation an accumulation of extracellular matrix components like proteoglycans can be visualized using tannic acid. These extracellular components might be related to the promotion of cellular events described during endocardial activation. The fusion of the septum primum with the atrioventricular (AV) endocardial cushions which would obliterate the foramen primum, occurs between mesenchymal tissues. Therefore, any alteration in the normal development of these mesenchymal tissues could be related to pathological cases of persistent atrial communications. Light microscopy preliminary observations of embryonic mouse heart indicate that septum primum mesenchymal tissue formation occurs similarly between mouse and chick embryos.

Influence of the mesenchymal microenvironment on myocardial and endocardial cell behaviour in experimental interaction with chick limb mesenchyme.

In an attempt to clarify the possible influence of the mesenchymal microenvironment in the differentiation of myocardial and endocardial cells, an "in vivo" transplantation experiment was performed in which the ventricular region of the heart (chick or quail) was placed in close association to the mesenchyme of the anterior chick limb to create an experimental interaction between myocardium and foreign mesenchyme. The results showed that after 48 h of tissue interactions the ventricular myocardium is incorporated into the mesenchyme of the anterior chick limb, changing its organization and cytological appearance. The myocytes tend to dissociate, exhibiting a less organized myofibrillar pattern. In addition, abundant extracellular matrix components made up of granular and fibrillar material were observed associated with the myocardial and the mesenchymal cell membranes as well as distributed in their surrounding microenvironment. The endocardium became discontinuous, due to detachment of the cells and emitted multiple pseudopodia and filopodia. These observations indicate that the mesenchyme from the anterior chick limb modifies the cellular behaviour and organization of the neighbouring myocardium and endocardium with which it interacts. We suggest that this might occur through participation of extracellular matrix components such as glycosaminoglycans, fibronectin and collagen which are known to act as macromolecular mediators in cell to cell interactions, cell migration and differentiation.

Mesenchymal tissue of the interventricular septum. Structural and ultrastructural study.

Light and electron microscopic studies of frontal and sagittal sections of embryonic chick hearts (Stages 25, 28-29), reveal mesenchymal tissue in the cephalic portion of the interventricular septum. The endocardium of this cephalic portion contains reoriented and invaginated cells with pseudopodia; in addition there are cells immediately subjacent to the endocardium. Similar cellular events take place during the formation of mesenchymal tissue in the atrioventricular and conotruncal regions. In these regions the mesenchymal tissue originates by means of an endocardial activation process. The structural characteristics of the formation of the cephalic portion of the interventricular septum suggest that local mesenchymal tissue is contributed by the endocardium. However, based upon the close anatomic relationship observed by us between the mesenchymal tissues of the atrioventricular canal, conotruncal region and the cephalic portion of the interventricular septum; we do not discard a contribution by migration of cells from atrioventricular and conotruncal regions to the interventricular septum.

Ultrastructural study of the myocardial wall of the atrio-ventricular canal during the development of the embryonic chick heart.

In the early stages of chick embryo development (days 3-5) the myocardium of the atrio-ventricular canal (AV) is continuous with the atrial and ventricular muscles; however, interruption of muscular continuity is observed at later stages (from day 6 to day 8). The most relevant event occurring at the AV canal region is the dissociation of the myocytes due to the loss of their cellular attachments, rather than an invasion of connective tissue cells (endocardial and sub-epicardial) located on both sides of the myocardium. In this study, particular attention was paid to the sequential changes that take place in the myocardium of this region, these being (1) a reduction in the number of desmosomes and intercalated discs with the subsequent appearance of large, inter-cellular spaces between myocytes; (2) migration of these cells through a complex extra-cellular matrix, to which it appears to be closely related, suggesting that the macromolecules of this matrix may be being synthesized by the myocytes, and may take part in the process of cardiac cell separation; (3) incorporation of the myocytes in the developing tricuspid valve, where they co-exist with fibroblasts. The results of the study correspond remarkably well to those previously carried out on the left AV canal myocardium, suggesting that the behaviour of the muscle is the same, at all points around the AV canal.