Research advances on embryonic diapause in mammals.

Embryonic diapause occurs in over 130 species of mammals. In embryonic diapause, there is a reversible cessation phase in embryo development and subsequent reactivation and continuation of development with no adverse effects. This allows animals to prolong gestation and give birth to offspring at a more favorable time from a survival perspective. Embryonic diapause is divided into two types: facultative diapause which is induced by physiological conditions and obligate diapause which is induced by season of the year. The process of embryonic diapause includes three phases: onset, maintenance, and reactivation. With facultative diapause the suckling stimulus promotes secretion of prolactin, which suppresses development and secretion activity of the corpus luteum (CL). The decrease of progesterone, secreted by CL, subsequently results in embryos in the diapause state. The embryonic diapause that occurs in mink is of the obligate type and is regulated by photoperiod. The short daylight (<12 h) before the vernal equinox induces an increase in the release of melatonin from the pineal gland. The secretion of prolactin is suppressed and the production of progesterone from CL is reduced. During these phases, many others factors that regulate embryonic and uterine status, hormonal profile, polyamines, and uterine secretion, have been monitored. In recent times, the understanding of the role of different molecular events in embryonic diapause has been advanced. The present review summarizes the research advances related to embryonic diapause to enhance the understanding of this phenomenon and to be considered when there are future research endeavors related to embryonic diapause.