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Hans Spemann won the Nobel Prize in Physiology or Medicine in 1935 for
foundational contributions to what is now the field of developmental biology.
Without those experiments, we wouldn’t know how an animal develops from a
small ball of cells into an organism with distinct, functioning parts.
That work is taught in every introductory development course.
However, if you look closely, you will notice that the work that claimed
Spemann the Nobel prize had another name on it: Hilde Mangold.
Hilde Mangold was a graduate student in Hans Spemann’s lab in
Freiburg, Germany, and it was her thesis work and experiments that helped
propel Spemann to scientific fame and glory,
though she herself would net little of the credit.
In the early 1920s, the field of developmental biology was just getting started.
Researchers were just beginning to probe the many complex steps required for a
single fertilized plant or animal egg cell, or zygote,
to form into an embryo, and from there into an adult organism.
This research wasn’t easy, because embryos are pretty small and fragile things.
To make matters worse, they’re also vulnerable to infection.
And researchers didn’t have antibiotics yet to add to their cultures.
Some things were already known, thanks to
observing embryos under a microscope.
Researchers understood that the zygote starts by undergoing several cell divisions
to become a blastula, a small, hollow cluster of cells.
At that stage, individual cells are known as blastomeres.
The blastula stage is where cells begin to specify, which is to say, they’re set down
the path to becoming a specific cell type.
Eventually, that will mean the difference between
becoming part of the nervous system versus, say, a skin cell.
However, researchers didn’t yet know what set cells down that path.
It could have been some kind of signal from their environment,
like some sort of chemical.
Or maybe becoming a specific cell type was an intrinsic part of the cell,
and different cells had different genetic information
in their nucleus that controlled their eventual fate.
We just didn’t know!
At the time, Hans Spemann’s laboratory was well known
for its ingenious experiments in amphibian embryos.
One of his first experiments in 1903 tested whether early newt blastomeres
all carried identical information in their nucleus,
and therefore had the same capacity to produce an organism.
In the early 1920s, Hilde Mangold, at the time Hilde Proescholdt,
joined Spemann’s lab at the University of Freiburg as a doctoral student.
And after a time, Spemann gave her the experiment that
would later change developmental biology.
Spemann had been interested for a while in the concept of a
developmental organizer, a tissue or cluster of cells that would
organize surrounding tissues into the parts of a mature organism.
He suspected that in amphibian embryos, this organizer was
located in a small region of the early embryo called the dorsal lip.
That part of the organism would develop into the notochord,
the embryonic precursor to the spinal cord.
Now, in order to test this, he had Mangold transplant the dorsal lip of one
amphibian embryo to the region of another embryo
that would become the belly region.
That’s an important detail, because the notochord
forms the spine on the opposite side of the organism.
If a belly is developing into a spine, you can pretty much tell
it’s because of your experiment.
They also used newt embryos of two different species,
and different colors, so they could identify the host and donor tissue.
If the dorsal lip had not been an organizer region, those cells
would have gotten sucked into the host embryo’s belly and blended in.
You’d get one newt with some cells the color of the host embryo
and some cells the color of the donor.
Or it could’ve died, but you know.
What happened was way weirder.
The embryo with two dorsal lips developed two notochords,
and given enough time, resulted in twin larvae attached at the belly.
One of those was the host color, while the other was
a mixture of both host and donor colors.
That tells us that the donor tissue was an organizer,
and it went and organized some of the host tissue just like it was supposed to.
Probably by sending them some signal -- which we now know to be the case.
These transplants were extremely difficult and labor-intensive, and
often resulted in failure.
At the end of two years of work, only six of Mangold’s embryos
survived the microsurgeries to make it into the publication.
The results were published in 1924, with Spemann’s name
coming before Mangold’s on what was technically her dissertation.
Some of Spemann’s male colleagues noted after the fact that
most other students were sole author of their dissertations.
Unfortunately, around the time that the paper went into publication,
Hilde Mangold died of an accident at the age of 26.
She did not live to see the impact of her work,
which is now a foundation of developmental biology.
Spemann won the Nobel as a result of this experiment as well as his
decades of work in early embryology.
And Hilde Mangold’s project remains one of the only
doctoral dissertations that directly helped result in a Nobel.
Despite sticking his name in front of hers on her work,
Spemann did credit Mangold numerous times in his Nobel lectures.
But her name would never have joined him on his award, because
Nobels are not granted posthumously.
And their joint discovery would go down in history
known as the “Spemann organizer.”
Fortunately, more and more developmental biologists are
now calling it the Spemann-Mangold organizer instead,
to commemorate both the amazing scientists who discovered it.
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