Sequential ovulation and fertility of polyoestrus in American black bears (Ursus americanus)

Review: Embryonic diapause in the European roe deer - slowed, but not stopped

Embryonic diapause in mammals describes a transient reduction of proliferation and developmental progression occurring at the blastocyst stage. It was first described in the European roe deer (Capreolus capreolus) in the 19th century, and later found to occur in at least over 130 mammalian species across several taxa. Diapause is often displayed as an interruption, a halt, or an arrest of embryonic development. In this review, we explore reduced, but not stopped pace of growth, proliferation and developmental progression during embryonic diapause and revisit early embryonic proliferation and continued slow development as peculiar phenomenon in the roe deer.

The enigma of embryonic diapause

Embryonic diapause – a period of embryonic suspension at the blastocyst stage – is a fascinating phenomenon that occurs in over 130 species of mammals, ranging from bears and badgers to mice and marsupials. It might even occur in humans. During diapause, there is minimal cell division and greatly reduced metabolism, and development is put on hold. Yet there are no ill effects for the pregnancy when it eventually continues. Multiple factors can induce diapause, including seasonal supplies of food, temperature, photoperiod and lactation. The successful reactivation and continuation of pregnancy then requires a viable embryo, a receptive uterus and effective molecular communication between the two. But how do the blastocysts survive and remain viable during this period of time, which can be up to a year in some cases? And what are the signals that bring it out of suspended animation? Here, we provide an overview of the process of diapause and address these questions, focussing on recent molecular data.