Studies on the Submicroscopical Structures of the Nurse Cells in Sea Urchin Ovary, with Special Reference to the Glycogen Particles

Abstract

The auxiliary cells, i. e., the nurse cells in the ovary of the sea urchin species,Hemicentrotus pulcherrimus and Heliocidaris crassispina at the early stage of oogenesis served as materials and investigated with particular reference to the glycogen particles by means of light and electron microscopy.
At the beginning of oogenesis in the ovary, the nurse cells show a peak of their development and a positive Pas-reaction. Thereby, the cells are arranged closely being partly connected with the “septate desmosomes” of Wood ('59) and filled up with large numbers of glycogen particles accompanying among them a small number of oil droplets and mitochondria, but few of endoplasmic reticulum and of other organoids and show almost no sign of glycogenesis. Of these cytoplasmic structures, the glycogen particles are identified as a particulate form of glycogen because of their variability in sizes, density as well as affinity for lead hydroxide and others, as recently Reveletal. ('60) noted. The glycogen particles in the present case are of ca.400-600 Å in diameter and of generally spherical or multiangular in shape but associated with no membraneous superficial structure. On the contrary, within the moderate dense amorphous ground substance of the particles a small number of fine particles of high electron density in ca.30-50 Å diameter i. e., the “elemental particles” are perceived.
With the progress of oogenesis in the ovary, however, the nurse cells begin to retract gradually and the glycogen particles in the nurse cells become dissolve to be discharged lastly from the cell surface into the intercellular space. Thereby, on the one hand, the glycogen particles appearing in the superficial cytoplasm begin to fall into a glycolysis being taken up into the small vesicles immediately beneath the plasm membrane and discharged through the cell surface. On the other hand, the other abundant glycogen particles in the deeper cytoplasm become to be broken down to make large dense aggregates of the “elemental particles ” from the glycogen particles. Among the “elemental particles ”, however, the ground substance of the glycogen particles become to dissolve and coalesce to make the ground substance of the large granules, into which a small number of “elemental particles ” right above noted, become to be arranged in concentric lamellar or whirl-like structure of less electron density.
In addition, in the deeper cytoplasm one can perceive often a region with “ heterolamellar structures ” where a few of mitochondria are surrounded with layered and flattened membranes to be swollen to make a large vacuole, containing probably a kind of nutrient substance.