Injection of a boar sperm factor causes calcium oscillations in oocytes of the marsupial opossum, <e1>Monodelphis domestica</e1>

At fertilisation, the sperm triggers an abrupt and transient increase in intracellular calcium ([Ca²⁺]<inf>i</inf>) in the oocyte cytoplasm. In eutherian mammals, oocytes exhibit multiple [Ca²⁺]<inf>i</inf> transients which are necessary for egg activation. We investigated [Ca²⁺]<inf>i</inf> in the marsupial opossum, <e1>Monodelphis domestica</e1>. 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⁺]<inf>i</inf>. Each oscillation travelled across and around the periphery of the egg in a wave-like manner. A control injection of KCl elicited no change in [Ca²⁺]<inf>i</inf>. This is the first observation of [Ca²⁺]<inf>i</inf> oscillations in the oocyte of a marsupial. The repetitive nature of the [Ca²⁺]<inf>i</inf> changes were more similar to those in oocytes of Eutheria than those in oocytes of non-mammalian vertebrates.