The distribution of polysaccharides during gastrulation and embryogenesis in the mouse embryo

Differentiation of the atrioventricular conducting system of the heart

The structure and function of the atrioventricular conducting system of the heart, and its relationship to the myocardium, are examined from a developmental point of view. On the basis of information derived from electron micrographic, electrophysiologic, and developmental studies of heart tissue, it is concluded that: (1) The idea of the syncytial nature of the heart lacks a sound anatomic basis. (2) Cytodifferentiation during embryonic cardiogenesis results in the development of at least 2 distinct populations of cells: those comprising the bulk of the myocardium and a second type, the specialized cells of the conductive tissue, which differs in histology, biochemistry, and physiology. (3) The common view of the myocardium as a spontaneously active tissue may require revision, since several lines of evidence appear to indicate that myocardial cells are quiescent until stimulated by an extrinsic source. Under normal circumstances, this stimulus source is the conductive tissue.

Distribution of maternal immunoglobulins in the mouse uterus and embryo in the days after implantation

The distribution of maternal immunoglobulins in the mouse uterus and embryo in the days after implantation has been studied on sections incubated with sheep Fab anti-mouse immunoglobulins labeled with peroxidase. At the time of implantation the blastocyst is already surrounded by immunoglobulins that are also present in the blastocoel and early endoderm; uterine glands contain large amounts of immunoglobulins. Later, immunoglobulins are concentrated in the vacuolated endoderm, then the visceral yolk sac and the embryonic gut. They are also present in the various cavities of the embryo. Trophoblast cells progressively contain increasing amounts of immunoglobulins. In the decidua, immunoglobulins coat the cells and also occasionally appear as cytoplasmic granules. The early presence of maternal immunoglobulins may represent the transfer of serum proteins as a means of nutrition for the embryo. It is also very likely to have an immunological significance in the protection of the embryo.