Development of the cytoplasmic membranous organelle in the endodermal cells of the yolk sac of the bat Tadarida brasiliensis cynocephala

Abstract

The “membranous organelle” in the cytoplasm of the endodermal cells of the yolk sac develops directly from the rough endoplasmic reticulum (ER). The organelle is very small, but recognizable prior to mid-gestation when the endodermal cells first hypertrophy, and at this time it consists of only a few hexagonal channels. The membranes forming the walls of the channels are continuous with the rough ER, and mitochondria are usually in close proximity to the developing structure. Glycogen is observed within the channels of the organelle even at this early stage, though none may be present in the remainder of the cytoplasm. The structure remains quite inconspicuous until about a month before birth when it increases in size, becoming as large as the nucleus, and is the dominant structure in the cytoplasm. At the height of its development it surrounds numerous lipid droplets of various sizes, and glycogen is at all times present within the membranous channels.