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

Abstract

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 KCl 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.