Electron microscope studies on the origin and maturation of yolk in oocytes of the tunicate, Ciona intestinalis.

Abstract

The origin of proteinaceous yolk in oocytes of Ciona, intestinalis appears to involve the activity of two kinds of vesicles derived from the Golgi complex. One kind of vesicle contains a granular product of considerable density while the contents of the other type of vesicle are of low density. Both types of vesicles become widely dispersed in the ooplasm during vitellogenesis. The high-density vesicle exhibits greater size variation than the lowdensity vesicle. The growing yolk globules possess an external often folded membrane enclosing both granular and vesicular elements. The granular-vesicular bodies are observed in wide size ranges and they appear to arise and increase in size by fusion or incorporation of numerous high-density vesicles, low-density vesicles, and smaller granular-vesicular bodies. The relationship of the developing yolk globules to ribosomes, pinocytotic vesicles, and vesicular endoplasmic reticulum is illustrated.