Atsumi Ukeshima

Observations of the primordial germ cells in blood samples from the chick embryo

Abstract Primoridal germ cells (PGCs) from the circulating blood in 2-day chick embryos were observed by histochemical techniques in smear preparation and by phase contrast microscopy in fresh samples. In the blood smear, PGCs were readily distinguished from blood cells by their large size (15–20 μm in diameter) and by the round and large nuclei (8–10 μm in diameter) occupying eccentrically the greater parts of the cells. Histochemically, they were demonstrated to contain abundant glycogen, a lesser amount of yolk granules (by the PAS reaction), and a large amount of lipid droplets (by the Oil red O and Sudan black B stains) in their cytoplasm. Alkaline phosphatase activity was proved slightly in their cytoplasm by the simultaneous diazo coupling method. In phase contrast microscopy, living PGCs in the blood and from the primitive gonad of 3-day embryos in parts of the examinations were observed to change their shape in somewhat amoeboid fashion, suggesting their capability for locomotion as a possible mechanism of the migration of PGCs in vivo .

OBSERVATIONS OF PRIMORDIAL GERM CELLS IN THE TURTLE EMBRYO (CARETTA CARETTA): LIGHT AND ELECTRON MICROSCOPIC STUDIES

Primordial germ cells (PGCs) in the turtle embryo (Caretta caretta) were observed with light and transmission electron microscopes. Identification of the PGCs for light microscopy was made by the periodic acid‐Schiff (PAS) technique. PGCs were first found in the yolk‐sac endoderm through the 5th to 6th day of development. PGCs freed from the endoderm then migrated to the root area of the dorsal mesentery and the coelomic angle between the 7th and the 11th day of development, and finally settled down in the gonadal anlage by the 14th day. Turtle PGCs were characterized by a large size (16 μm in diameter) and large nuclei with distinct nucleoli, and by the presence of large numbers of lipid droplets, yolk platelets and glycogen particles in the cytoplasm. Cell organelles were well‐developed in PGCs at later stages. Amoeboid features of the PGCs were observed in the mesenchyme, indicating active locomotion. PGCs were usually surrounded or encircled by neighboring somatic cells. No intravascular PGCs were detected at any stage of development examined.

Ultrastructure of primordial germ cells in the early chick embryo

Primordial germ cells (PGCs) of vertebrates appear in the extragonadal (in amniotes, extraembryonic) site at very early stages of development and migrate to the gonadal anlagen with the advance of embryonal development (e.g., 1–4). PGCs are identifiable by morphological or histochemical properties. These properties provide effective means by which their migratory pathway to the gonads may be traced. As to the morphological properties, PGCs are large in size and have a prominent nucleolus, and large amount of glycogen and lipid. Of the histochemical properties, periodic acid-Schiff (PAS) and alkaline phosphatase reactions have been utilized. For example, the PAS staining for glycogen has been effective for the identification of PGCs in chicks (5–11), turtles (4), lizards (12) and humans (13). Alkaline phosphatase activity has been used for identification of these cells in mice (14–18) and humans (19, 20)