Injection of a boar sperm factor causes calcium oscillations in oocytes of the marsupial opossum, Monodelphis domestica

At fertilisation, the sperm triggers an abrupt and transient increase in intracellular calcium ([Ca²⁺]_i) in the oocyte cytoplasm. In eutherian mammals, oocytes exhibit multiple [Ca²⁺]_i transients which are necessary for egg activation. We investigated [Ca²⁺]_i in the marsupial opossum, Monodelphis domestica. Embryo development in this therian mammal is quite distinct from that in most Eutheria. Oestrus was induced in an adult female opossum by introduction of a male into her cage. Injection of a boar sperm extract induced repetitive increases in [Ca²⁺]_i. Each oscillation travelled across and around the periphery of the egg in a wave-like manner. A control injection of KCI elicited no change in [Ca²⁺]_i. This is the first observation of [Ca²⁺]_i oscillations in the oocyte of a marsupial. The repetitive nature of the [Ca²⁺]_i changes were more similar to those in oocytes of Eutheria than those in oocytes of non-mammalian vertebrates.