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The hawksbill sea turtle (Eretmochelys imbricata) is a critically endangered species at a risk of extinction. Preservation of the genomic and cellular information of endangered animals is important for future genetic and biological studies. Here, we report the efficient establishment of primary fibroblast cultures from skin tissue of the hawksbill sea turtle. We succeeded in establishing 19 primary cultures from 20 hawksbill sea turtle individuals (a success rate of 95%). These cells exhibited a fibroblast-like morphology and grew optimally at a temperature of 26°C, but experienced a loss of viability when cultured at 37°C. Chromosomal analysis using the primary cells derived here revealed that hawksbill sea turtles have a 2n = 56 karyotype. Furthermore, we showed that our primary cell cultures are free of several fish-related viruses, and this finding is important for preservation purposes. To our knowledge, this report is the first to describe primary cell cultures established from normal tissues of the hawksbill sea turtle. The results will contribute to the preservation of biodiversity, especially for the sea turtles that are critically endangered owing to human activities.

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Conservation of the genetic resources of endangered animals is crucial for future generations. The loggerhead sea turtle (Caretta caretta) is a critically endangered species, because of human hunting, hybridisation with other sea turtle species, and infectious diseases. In the present study, we established primary fibroblast cell lines from the loggerhead sea turtle, and showed its species specific chromosome number is 2n = 56, which is identical to that of the hawksbill and olive ridley sea turtles. We first showed that intensive hybridization among multiple sea turtle species caused due to the identical chromosome number, which allows existence of stable hybridization among the multiple sea turtle species. Expressions of human-derived mutant Cyclin-dependent kinase 4 (CDK4) and Cyclin D dramatically extended the cell culture period, when it was compared with the cell culture period of wild type cells. The recombinant fibroblast cell lines maintained the normal chromosome condition and morphology, indicating that, at the G1/S phase, the machinery to control the cellular proliferation is evolutionally conserved among various vertebrates. To our knowledge, this study is the first to demonstrate the functional conservation to overcome the negative feedback system to limit the turn over of the cell cycle between mammalian and reptiles. Our cell culture method will enable the sharing of cells from critically endangered animals as research materials.

Journal of Cellular Biochemistry Cover: The cover image, by Tomokazu Fukuda et al., is based on the Article

Prairie voles show strong pair bonding with their mating partners, and they demonstrate parental behavior toward their infants, indicating that the prairie vole is a unique animal model for analysis of molecular mechanisms of social behavior. Until a recent study, the signaling pathway of oxytocin was thought to be critical for the social behavior of prairie voles, but neuron-specific functional research may be necessary to identify the molecular mechanisms of social behavior. Prairie vole pluripotent stem cells of high quality are essential to elucidate the molecular mechanisms of social behaviors. Generation of high-quality induced pluripotent stem cells (iPSCs) would help to establish a genetically modified prairie vole, including knockout and knock-in models, based on the pluripotency of iPSCs. Thus, we attempted to establish high-quality prairie vole-derived iPSCs (pv-iPSCs) in this study. We constructed a polycistronic reprogramming vector, which included six reprograming factors (Oct3/4, Sox2, Klf4, c-myc, Lin28, and Nanog). Furthermore, we evaluated the effect of six reprogramming factors, which included Oct3/4 with the transactivation domain (TAD) of MyoD. Implantation of the pv-iPSCs into immunodeficient mice caused a teratoma with three germ layers. Furthermore, the established pv-iPSCs tested positive for stem cell markers, including alkaline phosphatase activity (ALP), stage-specific embryonic antigen (SSEA)-1, and dependence on leukemia inhibitory factor (LIF). Our data indicate that our newly established pv-iPSCs may be a useful tool for genetic analysis of social behavior.

Nonhuman primates are useful animal models for the study of human diseases. However, the number of established cell lines from nonhuman primates is quite limited compared with the number established from other experimental animals. The establishment of nonhuman primate cell lines would allow drug testing on those cell lines before moving experiments into primates. In this study, we established nonhuman primate primary cell lines by introducing the genes for CDK4R24C, cyclin D1, and hTERT. These cell lines proliferated more rapidly than primary cells and bypassed cellular senescence. Karyotype analysis showed that the chromosome patterns were intact in the immortalized cell lines. Furthermore, we showed that the expression of introduced genes could be precisely controlled through the Tet-Off system with the addition of doxycycline. The present study shows that introduction of the CDK4R24C, cyclin D1, and hTERT genes are effective methods of establishing nonhuman primate cell lines.

The prairie vole (Microtus ochrogaster) shows social behaviors such as monogamy and parenting of infants with pair bonding. These social behaviors are specific to the prairie vole and have not been observed in other types of voles, such as mountain voles. Although the prairie vole has several unique characteristics, an in vitro cell culture system has not been established for this species. Furthermore, establishment of cultured cells derived from the prairie vole may be beneficial based on the three Rs (i.e., Replacement, Reduction, and Refinement) concept. Therefore, in this study, we attempted to establish an immortalized cell line derived from the prairie vole. Our previous research has shown that transduction with mutant forms of cyclin-dependent kinase 4 (CDK4), cyclin D, and telomerase reverse transcriptase (TERT) could efficiently immortalize cells from multiple species, including humans, cattle, pigs, and monkeys. Here, we introduced these three genes into prairie vole-derived muscle fibroblasts. The expression of mutant CDK4 and cyclin D proteins was confirmed by western blotting, and telomerase activity was detected in immortalized vole muscle-derived fibroblasts (VMF-K4DT cells or VMFs) by stretch PCR. Population doubling analysis showed that the introduction of mutant CDK4, cyclin D, and TERT extended the lifespan of VMFs. To the best of our knowledge, this is the first report describing the establishment of an immortalized cell line derived from the prairie vole through the expression of mutant CDK4, cyclin D, and human TERT.