Deep in a lab at Friedrich Schiller University Jena, biologist Dr. Stanislav Kremnyov bent over a microscope, guiding a needle finer than a spider’s thread into an embryo no larger than a human hair. The organism was a comb jelly—Mnemiopsis leidyi—whose translucent, pulsating body belies the revolutionary secrets hidden in its earliest development. What Kremnyov and his team discovered there is reshaping our understanding of animal life: a tiny cluster of cells in this ancient creature functions just like the embryonic “organizer” first identified in frogs nearly a century ago. This signaling center, once thought to be a hallmark of complex vertebrates, now appears to be a shared inheritance from the very dawn of multicellular animals.
The organizer, first discovered in 1924 by Hans Spemann and his student Hilde Mangold, is a group of cells that orchestrates the body’s layout—determining which end becomes the head, which side the left, and how organs align in three-dimensional space. Spemann won the Nobel Prize for this work, but the full evolutionary reach of the organizer remained a mystery—until now. By transplanting a 20-micrometer fragment of the blastopore from one Mnemiopsis embryo into another, the Jena team triggered the formation of a second body axis, just as Spemann and Mangold did in amphibians. Even more astonishing, when they transplanted the same tissue into a sea anemone embryo—belonging to a lineage that split from comb jellies some 60 million years later—the organizer still worked, coaxing the host embryo to form a duplicate axis.
“This is because, according to current understanding, the lineage of the Ctenophora—the scientific name for comb jellies—diverged from ours around 700 million years ago,” explains Prof. Dr. Andreas Hejnol, who led the study. The fact that this mechanism persists across such evolutionary distance suggests that the genetic blueprint for complex body plans emerged just once, at the root of animal evolution. The team even identified the gene responsible for organizer formation in the sea anemone, marking the first time this genetic pathway has been pinpointed in cnidarians.
The precision required for these experiments was extraordinary. With embryos measuring just 120 micrometers across, the work demanded near-impossible delicacy. “The editor of Nature suspected that these experiments must have felt like dissecting clouds,” Hejnol recalled—a poetic nod to the fragility of life at this scale. Yet within those gossamer structures lies a universal code, one that has guided animal development for hundreds of millions of years.
This discovery doesn’t just rewrite textbooks—it redefines our place in the tree of life. The same cellular choreography that shapes a human embryo also guides a comb jelly through its earliest moments. As research continues, scientists may uncover even deeper links across the animal kingdom, revealing a shared developmental language written in the genes of creatures as distant as jellyfish and jaguars.