Fire Ant Vitellogenesis (Egg Yolk Formation)

To observe the sequence of events necessary for fire ant vitellogenesis, watch the movie on the left.

These animations have been prepared with the objective of serving as teaching tutorials to assist undergraduate students in conceptualizing the complex dynamics of physiological processes -- especially as they relate to insects. I am sharing these animations with my colleagues that wish to link to them, or refer them to their students for the purpose of illustrating course lecture topics.

As a courtesy, to help me evaluate the usefulness of the animations, if you use them in your teaching, please send me an e-mail at: llkeeley@tamu.edu, and let me know if they are helpful. I would also point out that these are works in progress, and will be updated occasionally with more scenes, voice-over, etc. to improve their usefulness for instruction

Instructions for playing the animation:

The movie starts on opening and the title page takes 10-20 seconds to play depending on the operating speed of your computer.

The MENU control allows you to review any scene without viewing the preceding scenes.

Use the blue control buttons to:

start: ( >> ),

stop: ( square ),

back up one frame: ( << )

restart the scene: ( I<< )

The fire ant queen synthesizes the precursor for the major yolk protein called vitellogenin in a tissue called the fat body.

The fat body releases the vitellogenin into the insect's hemolymph and it is transported throughout the body and into contact with the ovaries.

Scene 1: Ovary Organization

The ovaries consist of a series of tubules called ovarioles. Each ovariole is divided into follicles that contain a series of increasingly mature oocytes (= egg cell). The oocytes are separated from each other by the follicle cells.

In addition to the oocyte, the follicles also contain nurse cells that contribute metabolites to the developing oocyte.

Scene 2: VG Uptake

When the oocyte initiates vitellogenesis (yolk formation) the follicle cells shrink and separate (= patency). This allows hemolymph to flow into the spaces between the follicle cells and contact the oocyte surface.

The surface of the oocyte contains membrane proteins that serve as vitellogenin receptors. The vitellogenin receptors bind the vitellogenin that is being transported from the fat body by the hemolymph.

Regions of the outer, plasma membrane of the oocyte accumulate a protein called clathrin. Clathrin identifies regions of the membrane that will form pits.

The vitellogenin receptors localize in the clathrin-coated pits and bind the vitellogenin. After binding the vitellogenin, the pits enclose the vitellogenin and bud into the cytoplasm of the oocyte and carry the vitellogenin into the oocyte (= endocytosis).

Scene 3: Yolk Granule Formation

Clathrin is recycled back to the plasma membrane to form new pits and the resulting vitellogenin-containing vacuole (= endosome) fuses with a transitional yolk body and releases the enclosed vitellogenin.

The endosome membranes and receptors recycle back to the plasma membrane to repeat the process.

The vitellogenin fuses with other droplets of vitellogenin in the transitional yolk body and is processed into the final, mature yolk protein called vitellin.