Japanese Researchers Create 'Planimal' Cells That Stably Retain Complete Algal Genomes

Researchers at the University of Tokyo have engineered hybrid "planimal" cells that successfully merge mammalian and algal genomes into a single living unit. The breakthrough, published on November 12, 2026, marks the first time animal cells have stably retained chromosome-scale plant DNA.[1][2]

The research team achieved this inter-kingdom fusion by introducing the genetic material of a photosynthetic alga—comprising tens of millions of base pairs—into cultured hamster cells. Rather than rejecting the foreign genetic code, the mammalian host cells integrated and maintained the algal chromosomes.[3][4]

This genetic retention persisted for more than 150 cell generations, a duration that surprised evolutionary biologists. The hybrid cells continued to replicate normally while carrying the massive payload of foreign DNA alongside their own native genetic instructions.[1][7]

Horizontal gene transfer—the passing of genetic material between distinct species—is common in bacteria but was thought to be strictly limited in complex eukaryotic organisms. Animals and plants typically inherit DNA vertically, passing it directly from parent to offspring.[1][5]

The Epigenetic Gatekeeper

To understand how the mammalian cells tolerated the algal chromosomes, the researchers investigated the host's cellular defense mechanisms. They discovered an "epigenetic gatekeeper" system that determines whether massive strands of foreign DNA are destroyed or adopted by the host.[1][3]

When foreign DNA enters a eukaryotic cell, it usually lacks the specific epigenetic markers—chemical tags on the DNA—that the host recognizes as its own. The host cell's defense systems typically identify this unmarked DNA as a viral threat and silence or degrade it.[1][4]

However, the University of Tokyo team found that the algal chromosomes possessed epigenetic signatures similar enough to the mammalian host to bypass these defenses. The host cell's machinery effectively misidentified the massive algal genome as native material, allowing it to remain intact.[3][7]

The researchers detailed the mechanism in their Nature Communications paper, noting that "epigenetic gatekeeping enables genome-scale horizontal gene transfer in eukaryotic cells." The finding suggests that complex organisms are far more capable of adopting massive foreign genetic sequences than previously understood.[1]

The scale of the transfer is unprecedented in laboratory conditions. Previous experiments in synthetic biology have successfully inserted single genes or small gene clusters into animal cells, but never an entire functioning genome from a completely different biological kingdom.[2][6]

Engineering Photosynthetic Animals

The creation of planimal cells opens radical new possibilities for synthetic biology and medical engineering. By demonstrating that animal cells can host plant genomes, scientists can now explore engineering mammalian tissues with plant-like capabilities, fundamentally altering cellular function.[4][5]

The most immediate theoretical application is the development of photosynthetic animal cells. If the retained algal genes can be fully expressed, researchers could potentially engineer mammalian tissues that generate their own oxygen and energy when exposed to specific wavelengths of light.[2][7]

Such a capability would revolutionize tissue engineering and organ transplantation. Lab-grown organs often fail because the inner tissues die from oxygen starvation before a functional blood vessel network can develop to support them during the critical early growth phases.[4][7]

Photosynthetic tissues could sustain themselves by producing oxygen internally during these early stages of growth. This light-driven life support system could overcome one of the primary bottlenecks in regenerative medicine, allowing for the cultivation of larger and more complex organ structures.[3][4]

AI

Beyond medicine, the agricultural sector is closely monitoring the research. The ability to transfer massive gene clusters across kingdoms could accelerate the development of crops with enhanced nutritional profiles or entirely novel disease resistance mechanisms borrowed from distant species.[5][6]

Evolutionary Implications

The University of Tokyo findings also force a reevaluation of evolutionary history. If epigenetic gatekeeping is the primary barrier to horizontal gene transfer, ancient eukaryotic cells may have exchanged massive amounts of DNA more frequently than the fossil record suggests.[1][3]

Biologists have long known that the mitochondria in animal cells and the chloroplasts in plant cells originated as free-living bacteria engulfed by larger host cells roughly 1.5 billion years ago. This endosymbiotic event was traditionally considered a rare evolutionary anomaly.[1][4]

The new research suggests that similar, large-scale genetic mergers might have occurred repeatedly throughout the evolution of complex life. If the epigenetic markers aligned by chance, entire chromosomes could have crossed between distinct species, driving rapid and unpredictable evolutionary leaps.[1][7]

To test the limits of this gatekeeping mechanism, the Japanese research team is already planning subsequent experiments. They aim to fuse mammalian cells with genomes from other distant species to map exactly which epigenetic signatures trigger rejection and which grant passage.[2][3]

The ultimate goal is to move from accidental compatibility to deliberate, programmable genome integration. By understanding the precise rules of this epigenetic gatekeeper, scientists hope to predictably engineer cells with entirely novel functions drawn from across the tree of life.[3]

Navigating Biological Boundaries

Despite the breakthrough, significant technical hurdles remain before planimal cells yield practical applications. While the mammalian cells stably retained the algal genome, they did not automatically express all the plant genes, leaving much of the foreign DNA dormant.[1][4]

Retaining a genetic blueprint is only the first step; reading and executing that blueprint requires compatible cellular machinery. The researchers must now find ways to activate the dormant algal genes, which currently show a low expression rate within the mammalian cellular environment.[1][7]

Furthermore, the long-term stability of these hybrid cells outside of carefully controlled laboratory conditions remains untested. The 150-generation milestone was achieved in isolated cell cultures, shielded from the complex immune responses that a living, multi-cellular organism would inevitably mount.[3][4]

Regulatory frameworks will also need to adapt to this new class of biological entity. Current genetic engineering guidelines are largely built around the transfer of individual genes, not the wholesale fusion of entire genomes from completely different biological kingdoms.[2][5]

As synthetic biology pushes past traditional taxonomic boundaries, international scientific bodies will have to define how these inter-kingdom hybrids are classified. Regulators must establish new protocols for monitoring and safely utilizing these engineered cells in medical and industrial applications.[5][6]

For now, the University of Tokyo team's achievement stands as a fundamental expansion of biological possibility. By proving that the genetic barriers between plants and animals are permeable, they have rewritten the established rules of cellular engineering and inheritance.[2][3]

The next phase of research will focus on mapping the specific epigenetic tags that grant foreign DNA safe passage. Once those molecular passwords are fully decoded, the creation of custom-built, multi-kingdom organisms may transition from a groundbreaking anomaly to a routine laboratory procedure.[1][7]

The implications for biodiversity conservation are also being discussed among geneticists. If entire genomes can be preserved within the robust cellular architecture of a different species, planimal technology might offer a novel method for banking the genetic material of critically endangered plants.[4][6]

Ultimately, the successful fusion of mammalian and algal cells demonstrates that the divisions between biological kingdoms are not absolute. As researchers continue to probe the epigenetic gatekeeper, the definition of what constitutes a single organism will become increasingly fluid.[1][3]