As a PhD student in the 1920s, embryologist Hilde Mangold conducted a strange experiment that transformed biology. She moved a lump of cells from embryos of one newt species into another. The transplanted cells caused a secondary ‘body axis’ to form in the host embryo, complete with a nervous system and a precursor to the spine. Mangold showed that much of the secondary body axis had been developed from the recipient embryo tissues.
The discovery of an embryonic ‘organizer’ that orchestrates the formation of a body axis “established a whole new area of developmental biology.” In a study published in Nature on 17 June [see attached pdf file], Kremnyov and his colleagues report the discovery of an embryonic organizer in marine predators called comb jellies (Ctenophora) and their successful transplantation into sea anemones (Cnidaria) — which belong to an entirely different phylum — forming extra mouths and pharynxes…!!
Many scientists (including GEITP) believe that comb jellies belong to the earliest branch of the multicellular animal family tree (i.e., earlier than sponges). Kremnyov and his colleagues argue the appearance of an organizer helped transform single-celled organisms into animals.
Graduate student Mangold died tragically in 1924 in a home gas explosion(!!!), but the discovery encouraged her supervisor, Hans Spemann, to perform additional experiments, leading to the 1935 Nobel Prize in Physiology or Medicine. Spemann’s laboratory became the center of the developmental biology world, attracting leading scientists to probe the organizer and look for similar capabilities in other developing tissues (e.g., transplanting tissue from snails and mouse kidneys into frog embryos) showing that these, too, possessed organizational activity. Later, in the 1980s and 1990s, scientists uncovered the molecular basis for organizers: signaling molecules known as morphogens.
Organizer cells and morphogens act like a construction foreman in the developing embryo, telling “the cells what they have to do and what they have to build”. Research into the organizer has been focused mostly on vertebrates. But in 2007, a team led by Technau discovered such cells in the embryos of starlet sea anemones (Nematostella vectensis) [Ref 2, below], which belong to an animal lineage that diverged after that of comb jellies. The findings raised questions about the evolutionary origins of the organizer. Until 2026, it was not known when the organizer emerged.
Kremnyov’s supervisor and study co-author, developmental biologist Andreas Hejnol at the Friedrich Schiller University Jena, maintains a menagerie of unusual invertebrates — including sea anemones, penis worms and flatworms — that he calls a microzoo. When he joined the lab, Kremnyov lab added a comb jelly (Mnemiopsis leidyi). M. leidyi are highly fecund and lay transparent embryos daily. While examining M. leidyi, Kremnyov observed the formation of embryo structures called blastopores — the location of the embryonic organizer in other animals. The structures first arise embryologally during a process called gastrulation, which occurs just a few hours after fertilization in comb jellies.
doi: https://doi.org/10.1038/d41586-026-01910-0
References
1. Kremnyov, S., Lebedeva, T., Genikhovich, G. & Hejnol, A. Nature https://doi.org/10.1038/s41586-026-10643-z (2026). [this pdf article is attached]
2. Kraus, Y., Fritzenwanker, J. H., Genikhovich, G. & Technau, U. Curr. Biol. 17, R874–R876 (2007).
The attached 2026 paper reports that the blastopore lip of the ctenophore Mnemiopsis leidyi, a member of the evolutionary sister group to all other metazoans, exhibits organizer activity. Authors show that transplanted fragments of blastopore lip tissue from M. leidyi gastrula induce secondary pharynx and mouth formation. Moreover, transphyletic transplantation experiments show that the blastopore lip of M. leidyi leads to the generation of a secondary body axis in embryos of the cnidarian Nematostella vectensis. Organizer function in M. leidyi requires both β-catenin and TGFβ signaling, and the TGFβ-family ligands probably provide this inductive capacity. These findings reveal the deep homology of the blastoporal organizer in ctenophores, cnidarians and vertebrates, implying the ancestral organizer role of the blastopore lip. Authors propose that the emergence of the organizer was an essential innovation that facilitated the change from the temporal cell differentiation of unicellular relatives to the spatial cell differentiation of the first multicellular embryo…!! 😊
Does this topic fit our GEITP theme of gene-environment interactions”…?? Yes. 😊 The environmental signal is differentiation; the genetic response is generation of morphogens during early embryogenesis. [Canonical morphogens have been described exclusively in animal systems. The concept was predicted and first named by Alan Turing in 1952]. The first morphogen (Bicoid) was discovered in the Drosophila embryo in 1988 (Driever and Nüsslein-Volhard, 1988).
In high school, yours truly used European earthworms for the annual science fair. He had read (in Scientific American, when it was still a science journal) that earthworms, like newts, can grow a new tail if they lose their tail. He wondered “how far anterior — still qualifies as “tail?” Cutting them into two pieces he found that incision at segment 17-18 — resulted in a variable response: some worms ended up with one head and two tails, others had two heads and one tail, and some had two heads and two tails…!! ☹
It turns out (in retrospect) that the segment 17-18 region was where there is a mixture of morphogens, some telling the animal to create another head and the other telling the animal to create another tail. [Although I had no idea what I had done], my physics and chemistry teachers entered my high school project in the annual Future Scientists of America High School Science Fair (sponsored by the National Science Foundation, Washington, D.C.), where I won First Place in the Biology Division…!! 😊
—DwN