Biodiversity loss is one of the defining environmental issues of the present century. In 2019, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) reported that in the best-studied taxonomic groups, most of the total extinction risk to species is estimated to have arisen during the past 40 years. Of an estimated 8 million animal and plant species, approximately 1 million are currently threatened with extinction. The situation is particularly serious for amphibians, of which more than 40 percent are threatened. Almost one-third of reef-forming corals, sharks and their relatives, and more than one-third of marine mammals are also threatened (IPBES, 2019).

　These global assessments are consistent with other indicators of biodiversity change. According to the Living Planet Report released by the World Wide Fund for Nature (WWF) in 2024, the Living Planet Index, an indicator of trends in monitored vertebrate populations, declined by an average of 73 percent between 1970 and 2020. This finding indicates a widespread decline in the average size of monitored populations of mammals, birds, reptiles, amphibians and fish worldwide (WWF, 2024). These declines are mainly driven by anthropogenic factors, including changes in land and sea use, direct exploitation of organisms, climate change, pollution and invasive alien species. Emerging infectious diseases can also place additional pressure on some wildlife populations.

　Addressing this biodiversity crisis requires not only the protection of species and their habitats in the wild but also complementary measures to secure biological materials and information for future conservation actions. In recent years, in-situ and ex-situ conservation have been increasingly integrated through the One Plan Approach (OPA). The OPA promotes the coordinated management of populations both inside and outside their natural habitats within a single conservation framework. Genetic resource banking (GRB), genomics and epigenetics can support this integrated approach by providing biological backup resources and scientific information for conservation planning.

　This special issue, entitled “Cell Preservation and Genomic Information Infrastructure Supporting Endangered Species Conservation,” includes five review articles. These articles focus mainly on two important subjects: the preservation of biological materials and the generation and use of genomic and epigenetic information. Through these reviews, we aim to show how cell preservation, germ cell preservation and molecular technologies can be implemented for endangered species conservation.

　Presently, many wild animals are classified as endangered species facing the critical crisis of extinction. In ex situ conservation programs, natural mating has been widely implemented in breeding programs to maintain and restore animal populations. It is essential, however, to preserve genetic diversity when reintroducing offspring produced through captive breeding into natural habitats, because loss of diversity may reduce long-term population viability and adaptability. In this context, gamete preservation, particularly sperm cryopreservation, plays a crucial role because sperm can be relatively easily collected from both live and dead individuals. Sperm have been preserved by freezing and freeze-drying, and their fertilizing ability has been maintained long-term. Moreover, reproductive technologies using preserved sperm, such as artificial insemination, in vitro fertilization and intracytoplasmic sperm injection, are indispensable to producing the next generation in conservation breeding programs. In this review, we summarize the latest technologies for male-germ-cell preservation and the application of these technologies to the production of subsequent generations in endangered species conservation.

　The preservation of germplasm has become key to conserving genetic resources and safeguarding species diversity. In avian species, the rapid decline of biodiversity necessitates the development of comprehensive genetic resource preservation strategies. While semen cryopreservation is widely used, it fails to capture maternally inherited genetic components, such as mitochondrial DNA and the female-specific W chromosome. Thus, developing a system for preserving female germplasm is essential. Avian embryos and oocytes are extremely difficult to cryopreserve due to their large yolk and complex structure. To overcome these biological constraints, two innovative approaches for female germline preservation have emerged: the utilization of primordial germ cells (PGCs) and ovarian tissue cryopreservation. This review summarizes current advancements in both methodologies, while comparing their technical maturity, scalability and practical applicability. PGC-based technologies, combined with germline chimera production, offer high scalability through in vitro expansion but remain constrained by the requirement for viable embryos. Conversely, ovarian tissue preservation, followed by orthotopic transplantation, provides unparalleled flexibility for field conservation, enabling the recovery of genetic material from post-mortem individuals. Finally, we propose a dual-track strategy that prioritizes the integration of ovarian tissue preservation to ensure that the maternal genetic contribution of every lost individual could be captured and potentially restored under appropriate conditions.

　Advances in whole-genome resequencing (WGS) have transformed conservation genetics by making it possible to obtain high-resolution assessments of genetic diversity, inbreeding and demographic history in endangered species, even from limited samples. This review synthesizes recent developments in genome-wide analyses, focusing on three key components: genome-wide heterozygosity, inbreeding estimation based on homozygosity-by-descent (HBD) and runs of homozygosity (ROH), and effective population size (Ne) inference. Genome-wide heterozygosity provides a robust measure of genetic diversity and can reveal delayed genetic erosion associated with recent population declines. Inbreeding analyses based on HBD and ROH enable the detection of both recent and historical inbreeding and their functional consequences, including mutation load and inbreeding depression. Meanwhile, Ne reconstruction using coalescent- and SFS-based approaches makes it possible to infer past demographic processes, bridging current genomic patterns with historical population dynamics. Importantly, this review highlights the limitations of relying on single metrics such as Ne or the Ne/N ratio alone, which can fail to detect cryptic genetic risks in both small and seemingly large populations. By integrating genome-wide diversity, inbreeding and demographic history, genomic approaches provide a comprehensive framework for identifying latent extinction risks arising from genetic erosion. Despite remaining challenges, including sample acquisition, DNA quality and assembly requirements, ongoing technological advances and collaborative frameworks support the application of genomic data in conservation. This integrative approach provides a foundation for evidence-based conservation management within a One Plan framework, enhancing the long-term viability of endangered species.

　Understanding aging in wild animals is fundamental to effective conservation, yet accurately determining age in free-ranging individuals remains a major challenge. While DNA provides stable genetic information for species identification, kinship and population structure, its sequence does not directly reflect age. Recent advances in epigenetics, particularly DNA methylation analysis, have enabled age estimation based on predictable, age-associated changes in gene regulation, offering a powerful alternative to traditional methods. Here, we review the development and application of DNA methylation-based age estimation across diverse animal taxa. We compare methodological approaches ranging from targeted techniques, such as methylation-sensitive high-resolution melting (MS-HRM), to genome-wide methods including reduced representation bisulfite sequencing (RRBS) and array-based platforms, highlighting their respective trade-offs in resolution, cost and scalability. We also examine how age estimation models are developed using known-age individuals and subsequently applied to wild populations using less-invasive samples such as feces, hair or feathers. Importantly, DNA methylation reflects not only chronological age but also aspects of biological aging, including physiological condition and environmental exposure. Integrating epigenetic age data into ecological frameworks can improve the estimation of population age structure and enhance demographic models. Overall, DNA-methylation-based age estimation represents a powerful bridge between molecular biology and conservation, providing new opportunities to better understand and manage wildlife populations in a rapidly changing world.

　As global biodiversity loss continues, conservation frameworks need to move toward more integrated approaches. This paper examines the role of Genetic Resource Banking (GRB) within the One Plan Approach (OPA), which integrates in situ and ex situ conservation into a single framework. By using cryopreservation at approximately −196 °C, GRB can preserve biological materials for long periods, providing a biological safety net and maintaining genetic diversity for future use. These resources also support Assisted Reproductive Technologies (ART) and serve as research infrastructure for genomic and disease-related studies. In Japan, a complementary system has been developed in which the National Institute for Environmental Studies (NIES) focuses on cultured somatic cells, while zoological institutions focus on germ cell preservation. The Okinawa rail (Hypotaenidia okinawae) provides a case study showing how cryopreserved cells can be used in conservation. These materials have supported genome analysis and in vitro infection studies to assess the risk of highly pathogenic avian influenza. Despite these advances, the gap between scientific potential and policy remains. This review suggests that cryopreservation should not be treated only as an emergency measure but should be introduced earlier as a preventive tool in conservation planning. Strengthening long-term infrastructure and coordination among institutions will be important to supporting the conservation of endangered species.