Fig. 1

Light microscopy images of the ovary, and of living oocytes from the starfish Patiria pectinifera before and after 1-methyladenine (1-MA) treatment. a A ripe ovary dissected from P. pectinifera, containing numerous fully grown immature oocytes. b Immature oocytes isolated from the ovary are surrounded by a layer of follicle cells (FC); the large nucleus termed germinal vesicle (GV) is visible in the cytoplasm. c Maturing oocytes treated with 1-MA for 50 min; at this point in maturation, the FC are clustered to one side of the oocytes. This is the optimal time at which eggs can be successfully fertilized (i.e., monospermic fertilization). d Fertilized eggs 3 min after insemination are surrounded by the fertilization envelope (FE) as a result of the cortical granules exocytosis. e In the absence of fertilization, the first polar body (PB) forms 65 to 75 min after 1-MA application. f Extrusion of the second polar body 105 to 115 min after fertilization of eggs matured for 50 min with 1-MA (arrow)