title: Prenatal regression of the trophotaenial placenta in a viviparous fish, Xenotoca eiseni.
abstract: 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.
authors.affiliation: Department of Growth Regulation, Institute for Frontier Medical Sciences, Kyoto University, Kawahara-cho 53, Shogo-in, Kyoto 606-8507, Japan.
authors.forename: Atsuo
authors.initials: A
authors.lastname: Iida
authors.affiliation: Department of Anatomy, Kitasato University School of Medicine 1-15-1 Kitasato, Sagamihara Kanagawa 228-8555, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Nishimaki
authors.affiliation: Department of Growth Regulation, Institute for Frontier Medical Sciences, Kyoto University, Kawahara-cho 53, Shogo-in, Kyoto 606-8507, Japan.
authors.forename: Atsuko
authors.initials: A
authors.lastname: Sehara-Fujisawa
mesh_terms: D000818:Animals; D053148:Caspase 3 / Q000096:biosynthesis; D004625:Embryo, Nonmammalian; D004817:Epidermis / Q000254:growth & development / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism; D005260:Female; D005399:Fishes / Q000254:growth & development / Q000378:metabolism*; D008648:Mesoderm / Q000254:growth & development / Q000378:metabolism; D010920:Placenta / Q000196:embryology* / Q000378:metabolism; D011247:Pregnancy
chemical_list: D053148:Caspase 3