Mead R A
Department of Biological Sciences, University of Idaho, Moscow 83843.
J Exp Zool. 1993 Sep 1;266(6):629-41. doi: 10.1002/jez.1402660611.
Embryonic diapause occurs in many species of vertebrates, but the physiological mechanisms which control this fascinating process are exceedingly different in the diverse groups which employ this reproductive strategy. In nonmammalian species and some bats, reduction in rate of embryonic development is temperature dependent, but this is not the case in most mammals. Development becomes arrested at the blastocyst stage of embryogenesis in mammals which exhibit delayed implantation, whereas postimplantation development is continuous but retarded in species exhibiting delayed development. The hormonal control of diapause is remarkably different in the various species. Pituitary secretion of prolactin prevents implantation in the tammar wallaby but hastens renewed development and implantation in the mink and spotted skunk. Ovariectomy results in the eventual death of blastocysts in mustelids but induces renewed development and implantation in the armadillo. Luteal function, as evidenced by elevated progesterone secretion, is essentially constant in the roe deer and armadillo, whereas the luteal cells fail to complete their differentiation and secrete low levels of progesterone in carnivores. Progesterone will induce implantation in the tammar wallaby, but estrogen is required to induce renewed development and implantation in rodents. Neither progesterone and/or estrogens appear to be capable of stimulating implantation in carnivores. The uterus plays an important role in maintaining the embryos in a viable state throughout the period of diapause. In many species the uterus undergoes histological changes and secretes increased amounts of protein, yet we still do not understand the role, if any, these proteins play in initiating renewed embryonic development. Thus the phenomenon of embryonic diapause still holds many mysteries for scientists to solve.
胚胎滞育在许多脊椎动物物种中都会发生，但在采用这种繁殖策略的不同类群中，控制这一奇妙过程的生理机制却极为不同。在非哺乳动物物种和一些蝙蝠中，胚胎发育速率的降低取决于温度，但在大多数哺乳动物中并非如此。在表现出延迟着床的哺乳动物中，胚胎发育在胚泡期停止，而在表现出延迟发育的物种中，着床后发育是连续的，但速度减缓。不同物种中滞育的激素控制差异显著。催乳素的垂体分泌会阻止袋狸胚胎着床，但会加速水貂和斑臭鼬胚胎的重新发育和着床。卵巢切除会导致鼬科动物的胚泡最终死亡，但会诱导犰狳胚胎重新发育和着床。如孕酮分泌升高所示，黄体功能在狍和犰狳中基本保持恒定，而在食肉动物中，黄体细胞未能完成分化，分泌的孕酮水平较低。孕酮会诱导袋狸胚胎着床，但在啮齿动物中，需要雌激素来诱导胚胎重新发育和着床。孕酮和/或雌激素似乎都无法刺激食肉动物的胚胎着床。在整个滞育期间，子宫在维持胚胎的存活状态方面起着重要作用。在许多物种中，子宫会发生组织学变化并分泌更多的蛋白质，但我们仍然不了解这些蛋白质在启动胚胎重新发育中所起的作用（如果有作用的话）。因此，胚胎滞育现象仍然有许多奥秘有待科学家去解开。
