Those keeping abreast of the synthetic biology space will already be familiar with the potential of induced pluripotent stem cells, or iPSCs, as one of the starting points for cultivated meat. Typically produced by reprogramming via transfection with the Yamanaka factors (Oct4, Sox2, Klf4, and c-Myc)^** (Takahashi et al., 2007), these cells can be differentiated into muscle or fat cells and used to grow animal products in the lab. Over in medical research, iPSCs are enabling disease modeling, regenerative medicine, and organoid development.

Yet the significance of these cells, specifically their capacity to become any cell type in the body, remains underappreciated by the broader scientific and synthetic biology community. Revive & Restore, the San Francisco-grown non-profit bringing biotech to conservation, is using stem cell technology to rethink the extinction crisis, establishing methods to grow embryos from endangered species in the lab 

The Promise of Induced Pluripotent Stem Cells (iPSCs)

iPSCs are produced from adult cells (e.g., from skin, blood, or even urine) that are reprogrammed back to a pluripotent state. These cells resemble those found in the earliest embryos, with the ability to give rise to an entire organism. Importantly, iPSCs can be produced non-invasively, bypassing the ethical hurdles associated with the use of embryonic stem cells. 

Since 2006, iPSCs have catalyzed innovation in human medicine, agriculture, and reproduction. With the capacity to reproduce any cell, tissue, or living system, including sperm & eggs, organoids, and embryos, these reprogrammed cells could be used to create offspring for critically endangered species, as well as engineer resilience to mitigate the looming threat of a sixth mass extinction event (Hutchinson et al., 2024). Converting a limited biobanked tissue sample to an inexhaustible, versatile stem cell line opens up a range of downstream applications for studying disease and enabling reproduction. Unfortunately, generating iPSCs across the evolutionary tree using traditional methods could take decades. 

The Challenge: Taking It One Species At A Time

Translating iPSC technology across diverse species would unlock the ability to generate precise cell types for any organism. However, evolution has created significant hurdles. Each species’ genome codes for unique regulatory mechanisms that can interfere with traditional reprogramming methods, making it difficult to induce true ground-state pluripotency.

Many labs report difficulties replicating the reprogramming process across different species. Cells can require additional transcription factors, small molecules, or varied culture conditions, and the troubleshooting process is labor-intensive and expensive. While iPSCs have been reported now for over 50 species, the cells produced are more often than not indicative of a later stage of embryonic development, unsuitable for differentiation to gametes or embryos.

The Opportunity: Leveraging High-Throughout Methods and AI

The field is delayed by a lack of standardized data for pluripotent cells from diverse vertebrate species. To move this field forward, we need multi-modal models that can detect patterns in pluripotent cells from diverged lineages and predict better ways to induce pluripotency across the evolutionary tree. There is now more than ever an opportunity to generate and utilize large-scale datasets to accelerate and predict better ways to produce iPSCs for any species.

Revive & Restore’s Program Manager, Dr. Ashlee Hutchinson, presented one version of how this might work at Reinvent Future’s event, “How Can AI Accelerate Progress In The Bio-World,” hosted in San Francisco in 2024.

While transcriptomic input data provides one approach, there will likely be multiple ways to look at this challenge, including protein engineering and chimeric/super factors, chromatin accessibility data, high-throughput screens of TF libraries followed by scRNA-seq, CRISPRa to screen endogenous regulation, or image-based machine learning to rapidly determine cell identity, as well as robotics and automation to upscale production of bioproducts. 

Enabling Reproduction: Producing Eggs & Sperm From Skin

In Japan, pioneers in the field, Katsuhiko Hayashi and Mitinori Saitou, have achieved full reconstitution of both male and female gametogenesis using iPSCs produced from mouse skin, fulfilling a game-changing milestone for the field (Hayashi et al., 2011; Hikabe et al., 2016). Remarkably, stem cell-derived gametes produced embryos that developed into healthy baby mice, which went on to reproduce naturally. This confirmed that sperm and eggs generated from skin cells can be used to create new individuals.

In the U.S., companies like Conception Bio, Gameto, and Ivy Natal are leveraging this technology for human fertility and agriculture. The ability to create sperm and eggs from any individual—yes, females could generate sperm, and males can generate eggs (Murakami et al., 2023)—could be one of the most profound scientific advances of our time.

For conservation, this breakthrough is just as critical. At the San Diego Zoo Wildlife Alliance and Leibniz Institute for Zoo and Wildlife Research, scientists have developed iPSCs for the Northern White Rhino, a species now down to just two remaining individuals—both female (Korody et al., 2021; Zywitza et al., 2022).

These iPSCs have since been differentiated into gamete precursor cells (Hayashi et al., 2022). The next challenge is to replicate the gonadal environment in vitro, allowing these primordial germ cells (PGCs) to undergo the complex changes required to become eggs and sperm. Guiding cells through meiosis in vitro remains a considerable technical challenge. Understanding how this process occurs naturally across a wide variety of species could yield fundamental insights into the pathways regulating this process. Here is another phenomenon where cross-species data is in woefully short supply. A collaborative effort is needed to harness this remarkable technology, establishing standardized transcriptomic and epigenetic data for cells progressing through the germline trajectory. 

Beyond Conservation: Growing Any BioProduct

Significantly, the applications of iPSC technology extend far beyond conservation. As global consortia move to sequence the genomes of all life on Earth, we may discover novel genes with the potential to solve some of biology’s greatest challenges. But sequencing alone is not enough. To harness the true potential of these discoveries, we need to start developing the ability to manipulate and express these genes in living systems—turning genetic knowledge into functional biotechnology. Stem cells are the foundational tool for making that vision a reality.

Revive & Restore is working to expand and integrate the field of stem cell science from a currently held dogma of two mutually exclusive research sectors - model versus wild species - to a catalytic vision encompassing all life on Earth. While the organization is motivated by the benefit of conserving species, this is undoubtedly an emerging economic growth area ready to move. Developing computational and experimental pipelines to predict pathways to pluripotency and cellular differentiation across the tree of life could accelerate multiple industries. The ability to generate cell, tissue, and organ systems from diverse species will drive breakthroughs in disease resistance, drug discovery, and vaccine development. High-throughput biomonitoring at a systems level could enable rapid testing of pollutants via a zoo-on-a-chip model. Additionally, expanding regenerative stem cell resources could transform veterinary medicine and uncover novel mechanisms relevant to longevity research. The cultivated meat industry will benefit from improved differentiation protocols, while agriculture could see advancements in reproduction and the creation of enhanced products. Thinking more creatively, this technology evokes the potential to grow living structures for bio-architectural purposes, with further stimulating directions continuing to emerge.  

Identifying the White Space

To spark inspiration and build a network of innovators, Revive & Restore hosted a catalytic workshop in 2023. This meeting aimed to accelerate advances in stem cell research, identify the white space, and incubate blue-sky ideas with leaders in the field.

Following the event, all participants co-authored a call-to-action published in Development, outlining the profound potential for leveraging this technology. Here, scientists across stem cell R&D appeal to the scientific community to prioritize a comparative approach for developing a deeper understanding of pluripotency across species. 

The organization continued to build momentum, establishing an Applied Stem Cell Conservation Fund, and in late 2024, a Request For Proposals was circulated designed to accelerate the application and utility of stem cell technology in the life sciences. The enormous response, just in, from the global community demonstrates the critical need to pour resources into this field. Revive & Restore received proposals encompassing work to derive and use iPSCs for wildlife disease, regenerative medicine, and, crucially, to produce offspring for endangered species. As a group, the proposals target over 100 wild species spanning the animal evolutionary tree, from the tiny Monarch butterfly to the great blue whale.

While individual projects are invaluable, a significant collaborative effort is needed to leverage interdisciplinary expertise and break down barriers between clinical research and biodiversity conservation. Essentially, we hold in our hands the technology to grow not only any organ or tissue from any species but the species themselves. Developing this potential across both non-profit sectors and industry could provide a powerful new approach for addressing the biodiversity and extinction crisis. 

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“We are as gods and might as well get good at it” - Stewart Brand, Co-Founder, Revive & Restore

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^**or the Thomson Factors (including Lin28 and Nanog)

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Ashlee Hutchinson, PhD., is a Program Manager at Revive & Restore.

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Revive & Restore is actively funding breakthrough stem cell research in conservation. If you’re at SynBioBeta, visit our booth #302 near Synbio Cafe to learn more about the bleeding-edge science we’re developing.

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References

• Hayashi, K., Ohta, H., Kurimoto, K., Aramaki, S., Saitou, M., 2011. Reconstitution of the mouse germ cell specification pathway in culture by pluripotent stem cells. Cell 146, 519–532. https://doi.org/10.1016/j.cell.2011.06.052
  
  
• Hayashi, M., Zywitza, V., Naitou, Y., Hamazaki, N., Goeritz, F., Hermes, R., Holtze, S., Lazzari, G., Galli, C., Stejskal, J., Diecke, S., Hildebrandt, T.B., Hayashi, K., 2022. Robust induction of primordial germ cells of white rhinoceros on the brink of extinction. Sci. Adv. 8, eabp9683. https://doi.org/10.1126/sciadv.abp9683
  
  
• Hikabe, O., Hamazaki, N., Nagamatsu, G., Obata, Y., Hirao, Y., Hamada, N., Shimamoto, S., Imamura, T., Nakashima, K., Saitou, M., Hayashi, K., 2016. Reconstitution in vitro of the entire cycle of the mouse female germ line. Nature 539, 299–303. https://doi.org/10.1038/nature20104
  
  
• Hutchinson, A.M., Appeltant, R., Burdon, T., Bao, Q., Bargaje, R., Bodnar, A., Chambers, S., Comizzoli, P., Cook, L., Endo, Y., Harman, B., Hayashi, K., Hildebrandt, T., Korody, M.L., Lakshmipathy, U., Loring, J.F., Munger, C., Ng, A.H.M., Novak, B., Onuma, M., Ord, S., Paris, M., Pask, A.J., Pelegri, F., Pera, M., Phelan, R., Rosental, B., Ryder, O.A., Sukparangsi, W., Sullivan, G., Tay, N.L., Traylor-Knowles, N., Walker, S., Weberling, A., Whitworth, D.J., Williams, S.A., Wojtusik, J., Wu, J., Ying, Q.-L., Zwaka, T.P., Kohler, T.N., 2024. Advancing stem cell technologies for conservation of wildlife biodiversity. Dev. Camb. Engl. 151, dev203116. https://doi.org/10.1242/dev.203116
  
  
• Korody, M.L., Ford, S.M., Nguyen, T.D., Pivaroff, C.G., Valiente-Alandi, I., Peterson, S.E., Ryder, O.A., Loring, J.F., 2021. Rewinding Extinction in the Northern White Rhinoceros: Genetically Diverse Induced Pluripotent Stem Cell Bank for Genetic Rescue. Stem Cells Dev. 30, 177–189. https://doi.org/10.1089/scd.2021.0001
  
  
• Murakami, K., Hamazaki, N., Hamada, N., Nagamatsu, G., Okamoto, I., Ohta, H., Nosaka, Y., Ishikura, Y., Kitajima, T.S., Semba, Y., Kunisaki, Y., Arai, F., Akashi, K., Saitou, M., Kato, K., Hayashi, K., 2023. Generation of functional oocytes from male mice in vitro. Nature 615, 900–906. https://doi.org/10.1038/s41586-023-05834-x
  
  
• Takahashi, K., Tanabe, K., Ohnuki, M., Narita, M., Ichisaka, T., Tomoda, K., Yamanaka, S., 2007. Induction of pluripotent stem cells from adult human fibroblasts by defined factors. Cell 131, 861–872. https://doi.org/10.1016/j.cell.2007.11.019
  
  
• Zywitza, V., Rusha, E., Shaposhnikov, D., Ruiz-Orera, J., Telugu, N., Rishko, V., Hayashi, M., Michel, G., Wittler, L., Stejskal, J., Holtze, S., Göritz, F., Hermes, R., Wang, J., Izsvák, Z., Colleoni, S., Lazzari, G., Galli, C., Hildebrandt, T.B., Hayashi, K., Diecke, S., Drukker, M., 2022. Naïve-like pluripotency to pave the way for saving the northern white rhinoceros from extinction. Sci. Rep. 12, 3100. https://doi.org/10.1038/s41598-022-07059-w