Insight into the function of voltage-sensing phosphatase in hindgut-derived pseudoplacenta of a viviparous teleost Xenotoca eiseni.

Nutrient absorption is essential for animal survival and development. Our previous study on zebrafish reported that nutrient absorption in lysosome-rich enterocytes (LREs) is promoted by the voltage-sensing phosphatase (VSP), which regulates phosphoinositide (PIP) homeostasis via electrical signaling in biological membranes. However, it remains unknown whether this VSP function is shared by different absorptive tissues in other species. Here, we focused on the function of VSP in a viviparous teleost Xenotoca eiseni, whose intraovarian embryos absorb nutrients from the maternal ovarian fluid through a specialized hindgut-derived pseudoplacental structure called trophotaenia. Xenotoca eiseni VSP (Xe-VSP) is expressed in trophotaenia epithelium, an absorptive tissue functionally similar to zebrafish LREs. Notably, the apical distribution of Xe-VSP in trophotaenia epithelial cells closely resembles zebrafish VSP (Dr-VSP) distribution in zebrafish LREs, suggesting a shared role for VSP in absorptive tissues between the two species. Electrophysiological analysis using a heterologous expression system revealed that Xe-VSP preserves functional voltage sensors and phosphatase activity with the leftward shifted voltage sensitivity compared with zebrafish VSP (Dr-VSP). We also identified a single amino acid variation in the S4 helix of Xe-VSP as one of the factors contributing to the leftward shifted voltage sensitivity. This study highlights the biological variation and significance of VSP in various animal species, as well as hinting at the potential role of VSP in nutrient absorption in X. eiseni trophotaenia.NEW & NOTEWORTHY We investigate the voltage-sensing phosphatase (VSP) in Xenotoca eiseni, a viviparous fish whose intraovarian embryos utilize trophotaenia for nutrient absorption. Although X. eiseni VSP (Xe-VSP) shares key features with known VSPs, its distinct voltage sensitivity arises from species-specific amino acid variation. Xe-VSP in trophotaenia epithelium suggests its involvement in nutrient absorption, similar to VSP in zebrafish enterocytes and potentially in species with similar absorptive cells. Our findings highlight the potential role of VSP across species.

Vitellogenin uptake activity in the intestinal ducts of intraovarian embryos in a viviparous teleost Xenotoca eiseni.

In the viviparous teleost species belonging to the family Goodeidae, intraovarian embryos absorb maternal supplements while they grow during the gestation period. They take up the components via trophotaeniae, a hindgut-derived placental structure. Our previous study using a goodeid species Xenotoca eiseni revealed that intraovarian embryos absorb the yolk protein vitellogenin (Vtg) via the trophotaenia. However, another group indicated yolk components accumulate in the intestinal lumen of X. eiseni embryos. Here, we investigated whether the intestinal duct is capable of protein uptake, as is the trophotaenia. Immunohistochemical studies indicated that endogenous vitellogenin is detected in the intestinal epithelial cells of the intraovarian embryo. Tracer analysis using FITC-Vtg also indicated that intestinal tissues can take up protein. The endocytosis-related genes expressed in trophotaenia were also detected in the intestinal tissues of the embryo. Lipid transporter genes which are not expressed in the trophotaenia were detected in the embryonic intestine. This evidence suggests that the intraovarian embryo of X. eiseni possesses two distinct sites for uptake of the maternal proteins. However, the presumed functions of the embryonic intestine and trophotaenia might be not identical. The study provides a new perspective on how mother-to-embryo matrotrophic interactions have changed in the evolution of viviparous teleosts.

Cubam receptor-mediated endocytosis in hindgut-derived pseudoplacenta of a viviparous teleost (Xenotoca eiseni).

Nutrient transfer from mother to embryo is essential for reproduction in viviparous animals. In the viviparous teleost Xenotoca eiseni (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 trophotaenia 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.

Sharply Angled Lateral Curvature Modification in Anal Fin of a Viviparous Fish, Xenotoca variata (Cyprinodontiformes: Goodeidae).

Almost all viviparous species possess male external genitalia; for example, the mammalian penis is an intromittent organ. Some live-bearing bony fish use their anal fins to assist in mating and internal fertilization. We previously reported a male-specific asymmetric curvature at the posterior end of the anal fin in Xenotoca eiseni, a viviparous fish of the family Goodeidae. However, three other goodeid species, Xenotoca melanosoma, Zoogoneticus quitzeoensis, and Chapalichthys pardalis, examined in that study possessed lesser anal fin curvature modifications as compared to those in the anal fin of X. eiseni. Here, we report the second case of acute-angled curvature modification of the male anal fin in the family Goodeidae. We obtained a dead specimen of the goodeid species Xenotoca variata from a city zoo in Japan, and the morphological and histological analyses indicated an acute-angled asymmetric curvature of the posterior end of the anal fin in X. variata, similar to that observed in X. eiseni in the previous study. However, in our previous report, obtuse-angled modification was only observed in one other Xenotoca species, X. melanosoma, and two species belonging to other genera, Z. quitzeoensis and C. pardalis. Therefore, our findings suggest that the acute-angled curvature in the male anal fin has been developed in the genus Xenotoca.

Glucose absorption activity and gene expression of sugar transporters in the trophotaenia of the viviparous teleost Xenotoca eiseni.

In viviparous reproductive systems, nutrient transfer from mother to embryo plays a critical role in the generation of offspring. Herein, we investigated the mother-to-embryo nutrient transfer machinery in the viviparous teleost Xenotoca eiseni, which belongs to the family Goodeidae. The intraovarian embryo absorbs maternal supplements via the hindgut-derived placental structure termed the trophotaenia. Tracer analysis indicated that the trophotaenia can take up glucose analogs in ex vivo cultured embryos. The candidate genes for absorption, sglt1, glut2, atp1a, and atp1b, were determined from published transcriptomes. These genes were expressed in the trophotaenia of X. eiseni embryos. Fluorescent immunohistochemistry of Na+/K+ ATPase indicated the polarity of epithelial cells in the trophotaenia. The presented evidence suggests that the epithelial cell layer transports monosaccharides from the apical membrane of epithelial cells in a basolateral direction. Taken together, this study provides insight into how maternal fish maintain their offspring during gestation and will aid in the development of strategies to improve offspring generation in these fish.

Design optimization of functionally graded lattice infill total hip arthroplasty stem for stress shielding reduction.

Reducing stress shielding of stem-inserted femurs in total hip arthroplasty caused by the high stiffness of the stem is an emerging medical engineering issue. In this study, a numerical design optimization methodology lattice infill stem was developed to realize a stem, balancing the low stiffness and strength requirements. Two pairs of models and loading conditions were introduced for the stress shielding and strength criteria. The objective function was set as the weighted sum of the criteria. Its effective density distribution was optimized by handling the representative size of the lattice as a design variable, assuming that the so-called body-centered cubic lattice was the base shape of the lattice. In the optimization, the approximated model of the lattice was handled as a solid material with the effective physical properties of the lattice derived by the homogenization method. After optimization, the detailed lattice stem geometry was modeled based on the obtained optimal lattice distribution, and the actual performance was numerically evaluated. The developed stem increased the stress applied to the remaining femur by 32.4% compared with the conventional stem.

Endocytosis-mediated vitellogenin absorption and lipid metabolism in the hindgut-derived placenta of the viviparous teleost Xenotoca eiseni.

Certain viviparous animals possess mechanisms for mother-to-embryo nutrient transport during gestation. Xenotoca eiseni is one such viviparous teleost species in which the mother supplies proteins and other components to the offspring developing in the ovary. The embryo possesses trophotaenia, hindgut-derived placental structure, to receive the maternal supplement. However, research on the molecular mechanisms underlying viviparous species is scarce in non-mammalian vertebrates, including teleosts. Thus, we conducted this study to investigate the mechanism for nutrient absorption and degradation in trophotaeniae of X. eiseni. A tracer assay indicated that a lipid transfer protein, vitellogenin (Vtg), was absorbed into the epithelial layer cells of the trophotaeniae. Vtg uptake was significantly suppressed by Pitstop-2, an inhibitor of clathrin-mediated endocytosis. Gene expression analysis indicated that the genes involved in endocytosis-mediated lipolysis and lysosomal cholesterol transport were expressed in the trophotaeniae. In contrast, plasma membrane transporters expressed in the intestinal tract were not functional in the trophotaeniae. Our results suggested that endocytosis-mediated lysosomal lipolysis is one of the mechanisms underlying maternal component metabolism. Thus, our study demonstrated how viviparous teleost species have acquired a unique developmental system that is based on the hindgut-derived placenta.

Histological observation of the reproductive system in a viviparous teleost Xenotoca eiseni Rutter 1896 (Cyprinodontiformes: Goodeidae).

Xenotoca eiseni is a viviparous teleost belonging to the family Goodeidae. Here, we report histological observations of the reproductive organs in an adult male, an adult female, a pregnant female with intraovarian embryo and an extracted embryo of X. eiseni. High-resolution images of haematoxylin-eosin-stained sagittal sections revealed the detailed structure of gonads, gametes and reproductive components of the mother-embryo relationship. In the male, mature spermatozoa in the epididymis formed sperm packages. In the female, oogenesis proceeded asynchronously in the ovarian wall, and various stages of oocytes were observed in single ovary. In both sexes, genital openings were located between the anus and anal fin. Developing embryos were observed in an ovary of the pregnant female. Fine structures of components of the mother-to-embryo nutrient supply, ovarian septum and trophotaenia were observed in the pregnant ovary. An immature gonad prior to gamete formation was identified in the extracted embryo. With the aim of supporting the development and extension of studies on this viviparous teleost, we have shared our histological images as raw data in an open online archive, the 'NAGOYA repository (http://hdl.handle.net/2237/00032456)'. Our goal is a comprehensive understanding of the viviparous system in fish using both histological observation and molecular biology methods including genomics and proteomics.