Cytoskeletal Structure and Dynamics in Fertilization and Early Development

Ever since antiquity, many theories have been proposed by philosophers and naturalists to explain the process of conception, the beginning of a new life. However, the observation that the fertilization process derives from the union of the pronuclei of a sperm and an egg was not known until the experimental works of the embryologists in the 19th century. In 1876, by using sea urchin eggs as an animal model, Oscar Hertwig demonstrated that this union was the essential prerequisite to the process of cleavage of the zygote. Later studies disputed this conclusion by showing that non-nucleated fragments from unfertilized eggs of sea urchin, starfish, and worm could develop normally after the addition of sperm (merogony). That the fertilization process may not be indispensable for development was also supported by Jacq Loeb’s discovery concerning artificial parthenogenesis in which unfertilized sea urchin eggs without sperm were made to develop into a living organism by treatments such as alkaline solutions, ultra-violet rays, and mechanical shock. Thus, the evidence that stimulation of the eggs alone was able to induce development brought Ernest Everett Just (1939) to state that “the egg-cell like many another living cell-nerve or muscle, for example- possesses independent irritability. It has full capacity for development. Neither spermatozoa nor experimental means furnish the egg with one.”

Recent results using modern imaging technology have provided evidence that F-actin dependent egg’s surface changes at fertilization are correlated with the quality of the fertilizable eggs. The ability of the egg to appropriately respond to the fertilizing sperm and sustain subsequent cell divisions is acquired during the maturation process of the oocyte, which is reflected in the structural changes of the egg surface and cortex. The fertilization process in the egg comprises a series of spatiotemporal events such as ionic fluxes, intracellular calcium release, separation of the vitelline layer from the plasma membrane in marine organisms or modification of the zona pellucida in vertebrates, sperm incorporation, the coming together of the egg and sperm pronuclei, and the formation of the cleavage-spindle. Recent results have indicated that exquisite regulation of the actin cytoskeleton is critical for oocyte maturation, fertilization, and cleavages in animal species.

In this Research Topic, we invite review and original research articles that address the dynamic roles played by actin and other cytoskeletal elements during (but not limited to):
- oocyte maturation
- sperm functioning
- gamete interaction
- fertilization
- cleavage.

We welcome articles describing basic research, translational research, and clinical studies on the given topic.