Iida Atsuo, Nishimaki Toshiyuki, Sehara-Fujisawa Atsuko
Department of Growth Regulation, Institute for Frontier Medical Sciences, Kyoto University, Kawahara-cho 53, Shogo-in, Kyoto 606-8507, Japan.
Department of Anatomy, Kitasato University School of Medicine 1-15-1 Kitasato, Sagamihara Kanagawa 228-8555, Japan.
Sci Rep. 2015 Jan 19;5:7855. doi: 10.1038/srep07855.
The trophotaenial placenta is a branching, ribbon-like structure that extends from the perianal region of the embryo in viviparous teleost fishes belonging to the family Goodeidae. It is a hindgut-derived pseudoplacenta, which contributes to absorbing maternal nutrients during the prenatal stage. The trophotaeniae are known to reduce at birth; however, no previous study has evaluated the removal mechanisms. We report here the analysis of the trophotaeniae using the goodeid fish species Xenotoca eiseni. The X. eiseni trophotaenia consists of an epidermal cell layer, mesenchyme, vasculature, and circulating erythrocytes. The trophotaeniae had preliminary regressed when the embryo was born. Immunohistochemistry indicated that caspase3-activated cells with fragmented nuclei are present in the regressed processes of the fry immediately after birth, but not in the vasculature and blood cells. This finding suggests that the trophotaenia is rapidly resorbed by apoptosis in the last phase of the pregnancy and that its circulatory pathway is maintained. Such prenatal regression of pseudoplacentae has not been reported in other viviparous vertebrates. On the other hand, similar apoptotic remodeling in the gut has been reported in amphibians, which is regulated by thyroid hormone. Thus, apoptotic regression of the trophotaeniae might occur in a manner similar to amphibian metamorphosis.
滋养带胎盘是一种分支状的带状结构，存在于胎生的谷鳉科硬骨鱼胚胎的肛周区域。它是一种源自后肠的假胎盘，在产前阶段有助于吸收母体营养。已知滋养带在出生时会退化；然而，此前尚无研究评估其清除机制。我们在此报告了对谷鳉科鱼类艾氏异诺卡鱼滋养带的分析。艾氏异诺卡鱼的滋养带由表皮细胞层、间充质、脉管系统和循环红细胞组成。胚胎出生时，滋养带已初步退化。免疫组织化学显示，出生后幼鱼退化过程中存在细胞核碎片化的caspase3激活细胞，但脉管系统和血细胞中不存在。这一发现表明，滋养带在妊娠后期通过凋亡迅速被吸收，其循环途径得以维持。这种假胎盘的产前退化在其他胎生脊椎动物中尚未见报道。另一方面，两栖动物肠道中也有类似的凋亡重塑现象，这是由甲状腺激素调节的。因此，滋养带的凋亡退化可能以类似于两栖动物变态的方式发生。
