MUSEUM OF POSTNATURAL HISTORY
SPARK
tHE SPARK OF LIFE
Every animal comes into being as a paradox. It starts as a fertilized egg—a single cell destined to become a complete organism—yet its own DNA remains silent. In these earliest moments of life, the embryo relies entirely on molecular components inherited from the mother to guide the first cell divisions. Then, after a short time—from a few hours to a few days depending on the species—something extraordinary happens: the genome gradually awakens. The organism begins to direct its own growth, shifting from maternal dependency to autonomous development. This transition is called zygotic genome activation.
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This universal phenomenon is fascinating in many respects. To uncover what drives genome activation, and to understand the broader principles of development and disease, scientists turn to a very small number of species known as model organisms—think of mice, rats and fruit flies. In 1972, George Streisinger at the University of Oregon added a new member to the roster. He was searching for an alternative to mice. Being an aquarium enthusiast himself, he found his answer during a visit to a local pet store in the city of Eugene, Oregon: the humble zebrafish (Danio rerio).
Casper zebrafish, a resident of the Center for Integrative Genomics (UNIL). Its transparency makes it easy to distinguish from transgenic lines, which otherwise resemble wild-type fish.
Genetically modified zebrafish (pou5f3:3xflag line)
Over the decades since, this small striped fish has proven itself an indispensable tool for studying fundamental questions of development, including the maternal-to-zygotic transition. Scientists rely on zebrafish to explore the molecular machinery that controls when and how genes are switched on and off during this crucial transition—all essential mechanisms for normal development and which, when disrupted, lead to disease. They can generate mutations and observe what happens when specific proteins are absent, present in reduced amounts, or lose their normal function.
Take pou5f3, for instance—a protein that controls the embryo's developmental potential and activates the genome. Scientists can tag such proteins with molecular markers to track where they go and how they behave within cells. This reveals the fundamental mechanisms at play: how proteins come together on DNA, the sequence of events that unfolds, and what guides them to activate the genome at just the right moment. These experiments shed light on this unique moment when every animal's genome first opens up to the spark of life.
Native to Asian rice paddies, zebrafish now also inhabit laboratory tanks. Center for Integrative Genomics, a research facility of the University of Lausanne.
