Human sperm and egg precursors created from stem cells

For the first time, researchers have
succeeded in creating human sperm and egg precursor cells from stem cells.
These precursors, called primordial germ cells, had been created before in mice but, until now, the human variant proved elusive. The precursor cells can be
used to study what happens very early on in embryo development, and could have
implications for research into ageing.

'The creation of primordial germ cells
is one of the earliest events during early mammalian development,' says Dr
Naoko Irie, first author of the paper from the Gurdon Institute at the University of Cambridge. 'It’s a stage we've managed to recreate using
stem cells from mice and rats, but until now few researchers have done this
systematically using human stem cells.'

Although the egg and sperm precursor
cells could have some application in infertility treatment down the line, their
main importance is as a model for early human development. Primordial germ
cells appear very early on in embryo formation, and being able to recreate this
step in a lab allows researchers to study some of the all-important processes that
shape early human development.

So far, scientists studying these early
processes have been using mouse cells, relying on our shared genes and
similarity in early development. However, the new findings show that this might not
be appropriate. 'It has highlighted important differences between
embryo development in humans and rodents that may mean findings in mice and
rats may not be directly extrapolated to humans', said Dr Irie.

The study team found that a gene, SOX17, had a key role in steering human cells to become different types of
precursor cells. This was surprising as the gene has no role in these processes
in mice.

'Mice are the key
model we use to study mammalian development and we extrapolate from mice to
humans,' Professor
Azim Surani, who led the research, told the
Guardian. 'This work tells us
that the extrapolation can be unreliable. I’m not saying that all work in mice
doesn't apply in humans, but there are fundamental differences we need to be
wary of.'

The primordial germ cells could also be
used to study why only certain traits are passed on to the next generation. During
our lives, environmental factors such as smoking or diet can modify gene
activity through epigenetic changes. In germ cells, some of these changes are
'reset'.

'This could tell us how to erase these epigenetic mutations. Epigenetics
is used to regulate gene expression, but in age-related diseases, these changes
can be aberrant and misregulate genes,' Professor Surani added.