Ca2+-induced change of dorsal-ventral polarity in frog (Rana temporaria) eggs

Abstract. The effect of local Ca²⁺ administration 10–20 min after fertilization and during artificial activation was examined in Rana temporaria eggs. Ca²⁺ was injected into the pigmented region near the boundary between pigmented and unpigmented domains. The locations of egg gray crescent (GC) and dorsal lip of blastopore (DLB), as predictors of the dorsal region in embryos, as well as the measurements of angles between GC middle and sperm entry site were observed. In more than 70% of the cases, microinjection of Ca^{2 +} into subcortical cytoplasm and egg pricking in high-Ca^{2 +} solutions induced GC and DLB formation near the injection site. The formation of Ca²⁺-induced GC occurred mostly as in control eggs. In addition premature displacement of the egg surface was observed near the prick site in high-Ca^{2 +} solutions. GC formation occurred by displacement of the pigmented surface in the same direction as earlier wound translocations. These results show that Ca²⁺ injection determines the direction of the surface movement.