Versatile utilities of amphibians (Part 3)

Part 1 and Part 2 of the special issue “Versatile Utilities of Amphibians” were released in August and September, respectively, containing 11 articles in total. This current special issue, Part 3, includes five articles (one research article, three short research articles, and one minireview). In this preface, we briefly walk you through those five articles as well as a research article already published in the October issue. The two research articles are as follows. Yamaguchi et al. (2022) examined the process of red blood cell (RBC) transition during metamorphosis in Xenopus laevis and Rana ornativentris by observing larval and adult globin types. Using thyroid hormone (TH) or anemia induction, they showed that RBC transition is regulated through both TH-dependent and -independent processes. Iwasa et al. (2022) investigated proliferation and neurogenesis in the adult forebrain of the Japanese red-bellied newt Cynops pyrrhogaster. By EdU labeling of proliferative cells and immunohistochemistry analyses at multiple time points over 2 months, they revealed that EdU-positive cells were initially Sox2-positive (stem cell marker), but 2 months later became Sox2-negative and NeuN-positive (neuronal marker), suggesting that proliferative cells in the adult newt telencephalon differentiate into neuronal cells. The following are three short research articles. Heijo et al. (2022) investigated how nuclear size is controlled by cytoplasmic factors and chromatin amounts (ploidy) by in vitro nuclear reconstruction assays with egg extracts and sperm chromatin obtained from the diploid species Xenopus tropicalis and the allotetraploid species X. laevis, respectively. They showed that nuclear size is controlled not only by the amount of chromatin (haploid or diploid) but also cytoplasmic factors (microtubule structures and nuclear import activity). This study is a good example of how to utilize these two amphibian species to investigate divergent biological phenomena. Seki-Omura et al. (2022) established a culture method for generating neurospheres from neural stem cells derived from the brain or spinal cord of the Iberian ribbed newt Pleurodeles waltl. They also showed that neurospheres differentiate into neurons, glial cells, and oligodendrocytes. Their method is expected to contribute to regenerative studies of the central nervous system. Okada et al. (2022) studied freeze tolerance in the Japanese tree frog Hyla japonica by measuring blood glucose levels and gene expression levels for glucose transporters and enzymes involved in glycogenolysis and gluconeogenesis in the liver. The data suggest the possibility that glucose acts as a cryoprotectant in H. japonica. The study demonstrates the applicability of amphibians in physiological research. In their mini-review, Zhou and Cho (2022) describe recent progresses in epigenetic studies of early Xenopus development. In particular, they focused on dynamic changes in histone modifications in relation to two phases of zygotic genome activation (ZGA), called minor ZGA and major ZGA, before gastrulation. These studies make use of the experimental advantages of Xenopus, such as the ability to obtain large numbers of synchronized embryos, to manipulate embryos for experimental procedures, and to microinject macromolecules into embryos for overand underexpression experiments, not to mention the application of modern single-embryo proteomic approaches, nascent transcriptomic methods, and chromatin conformation capture. As you can see, studies from broad research fields have been published in this special issue, demonstrating the “colorfulness” in versatility of amphibians. Please look forward to reading more in following issues, as we plan to further publish more than 10 additional articles, with the intention to compile a “polychromatic” catalog of current amphibian studies.