job of constructing life. He is one of an elite cohort of
scientists trying to build a replica of the human embryo
from the ground up to try to understand just how we
are made – and where it can all go horribly wrong.
This area of science aims to alleviate the gamut of
reproductive misery, from the anguish of infertility
and miscarriage to gathering information about drugs
like Thalidomide, which seem innocuous but have
grave consequences if taken during pregnancy.
Fu’s bundles of cells, dubbed embryoids, could
be used to screen drugs for toxicity in the womb.
They might also unravel the mystery of why two out
of every five pregnancies fail before 20 weeks. But
these scientists, tinkering at the dawn of life, don’t
know how far the cells can develop. There is talk their
creations could one day provide a source of organs
for transplant. The spectre of a baby in a dish looms
ominously in the public imagination.
Which is why Fu’s bit of kit, written up inNature
in September and described by leading embryologist
Ali Brivanlou as “a major advance in the knowledge
of early human development”, is also an invitation for
humanity to do some circle time on what it means to
build a human.THE INVENTION THAT’S CREATEDthis excitement is a
simple-looking chamber with three channels. In one,
Fu places pluripotent stem cells, blue-sky building
blocks that can become almost any human cell. They
are immortal and can be frozen and thawed, forming a
renewable resource that can be used for years.
Some of these are embryonic stem cells, originally
derived from human IVF embryos. Fu also uses
“induced pluripotent stem cells” – iPS cells for short- that come from adult skin cells re-programmed
back to a primal state.
In the second channel Fu pours a liquid containing
morphogens, the fertilisers that hurry stem cells on
with the job of remaking themselves over and over. In
the third, he lays a gel to support the growing masses,
each one hived into its own mini-domain by evenly
spaced support posts – the ziggurats.
In many respects there’s nothing novel about this.
Researchers the world over are growing stem cells
into structures that mimic the early embryo, before
getting them to switch course in the first few weeks
and become heart, brain or kidney cells.
These grow to make mini organs or “organoids”,
about the size of a stunted chickpea, that are used to
model diseases on the lab bench and test if drugs or
gene tweaks might be a cure.
But Fu is aiming to make the whole shebang.
There’s no diverting cells off into hearts and brains –
rather, he wants them to run their course and become
something that resembles the early human embryo.
Fu has pushed these embryoids as far as anyone’s
EXPLAINER HUMAN EMBRYO DEVELOPMENT
DAY 0
Sperm and egg nuclei
fuse, forming a fertilised
egg – zygote – and rapid
division begins.DAY 4
Morula has formed from
16-32 blastomeres, with
fluid filled cavity inside
morula.DAY 6
Blastocyst forms, with
an inner cell mass
(ICM) and outer layer –
the trophoblast.DAY 7
The ICM – which will
become embryonic stem
cells, develops.DAY 8
The ICM separates into
epiblast and hypoblast
cells.DAY 8
Implantation
occurs; cells start to
differentiate.WEEK TWO
Embryonic disc separates
yolk and amniotic sacs.WEEK TWO
Gastrulation; the
primitive streak forms.WEEK TWO
Cells in different
regions differentiate.CDBCDAPRIMITIVE STREAK
Defines the axes of asymmetry that will define differences in the embryo’s left
and right; front and back; and top and bottom.AB EMBRYONIC DISCThe two layers of cells that will become the embryo.EPIBLAST & HYPOBLAST CELLS
These cells form the divide that allows the amniotic cavity to develop.CELL DIFFERENTIATION
Epiblast cells become endoderm, ectoderm and mesoderm (see page 75).72 – COSMOS Issue 86
STEM CELL FRONTIER