RT Journal Article SR Electronic T1 Cubam receptor-mediated endocytosis in hindgut-derived pseudoplacenta of a viviparous teleost Xenotoca eiseni JF bioRxiv FD Cold Spring Harbor Laboratory SP 2021.02.01.429082 DO 10.1101/2021.02.01.429082 A1 Atsuo Iida A1 Kaori Sano A1 Mayu Inokuchi A1 Jumpei Nomura A1 Takayuki Suzuki A1 Mao Kuriki A1 Maina Sogabe A1 Daichi Susaki A1 Kaoru Tonosaki A1 Tetsu Kinoshita A1 Eiichi Hondo YR 2021 UL http://biorxiv.org/content/early/2021/03/22/2021.02.01.429082.abstract AB Nutrient transfer from mother to the embryo is essential for reproduction in viviparous animals. In the viviparous teleost Xenotoca eiseni belonging to the family Goodeidae, the intraovarian embryo intakes the maternal component secreted into the ovarian fluid via the trophotaenia. Our previous study reported that the epithelial layer cells of the trophotaenia incorporate a maternal protein via vesicle trafficking. However, the molecules responsible for the absorption were still elusive. Here, we focused on Cubam (Cubilin-Amnionless) as a receptor involved in the absorption, and cathepsin L as a functional protease in the vesicles. Our results indicated that the Cubam receptor is distributed in the apical surface of the trophotaenia epithelium and then is taken into the intracellular vesicles. The trophotaenia possesses acidic organelles in epithelial layer cells and cathepsin L-dependent proteolysis activity. This evidence does not conflict with our hypothesis that receptor-mediated endocytosis and proteolysis play roles in maternal macromolecule absorption via the trohotaenia in viviparous teleosts. Such nutrient absorption involving endocytosis is not a specific trait in viviparous fish. Similar processes have been reported in the larval stage of oviparous fish or the suckling stage of viviparous mammals. Our findings suggest that the viviparous teleost acquired trophotaenia-based viviparity from a modification of the intestinal absorption system common in vertebrates. This is a fundamental study to understand the strategic variation of the reproductive system in vertebrates.Competing Interest StatementThe authors have declared no competing interest.