Ca(2+) signaling during activation and fertilization in the eggs of teleost fish

Interest in the morphological and physiological events that take place during fertilization in fish eggs began as early as the late 1800s. In these initial studies, and up to the present day, fertilization has been investigated in a range of different fish species. In this short review, we focus on just one aspect of fertilization in fish; the role of Ca(2+) signaling. Somewhat surprisingly, to date, the Ca(2+) dynamics at activation/fertilization have been visualized in only two teleost species, the medaka (Oryzias latipes) and the zebrafish (Danio rerio), where their year-round breeding potential and small size, as well as the optical clarity of the eggs and ex utero fertilization, have made them the model of choice of researchers studying fertilization and early development. In these two species, activation/fertilization is accompanied by a single self-propagating Ca(2+) wave, unlike the multiple regenerating waves reported for mammals, ascidians, certain amphibians (urodeles) and annelids. During medaka and zebrafish fertilization, the Ca(2+) wave is initiated at the micropyle, the point of sperm/egg contact located at the animal pole, and then it propagates at ∼10-12μm/s to its antipode at the vegetal pole.