My name is Ruth Lehmann, and I work at
the Howard Hughes Medical Institute and
at the Helen and Martin Kimmel Center for
Biology at the Skirball Institute
at NYU Medical School.
I would like to talk today
about germ cell specification,
going all the way from how
germ cells initially form,
to how eventually a gonad forms, and how
germ cells become germ line stem cells.
What this is really about is
that germ cells are forever.
While, when a fertilized egg cell starts
to begin its development into its zygote,
the soma will eventually die earlier or
However, a primordial germ cell that
will be set aside really early during
the development of the embryo
will go on forever.
Because if it is allowed to give
rise to a germ line stem cell and
then produce either egg or sperm,
it can give rise to another organism.
when we think about germ line development,
we really have to think about
a life cycle of the germ line.
And also, to some extent, an eternal
cycle, because this gives not only
rise to a new organism, but it also,
the germ cell, maintains the species.
So I would like to introduce the lifecycle
of the germ line, and in particular,
germ cells that we work on, and
that is the Drosophila germ cells.
So we have here the life
cycle in the center,
where a fly female meets the fly male.
And their product is then fertilized egg,
which will develop into an embryo.
And very early on,
the primordial germ cells will form and
be set aside in this embryo.
These germ cells will then
migrate to the embryonic gonad,
which is the somatic part of the gonad.
And here, sexual identity will
be bestowed on the germ cells.
And during three larval stages,
this embryonic gonad will grow
into a larval and pupal gonad.
And during that time, primordial germ
cells will keep on dividing, and
there will be many,
many more of these primordial germ cells.
Until eventually, in the female,
the germ cells are set aside,
some of them becoming
germ line stem cells.
And so, in my presentation today,
I will focus a lot on how primordial
germ cells are initially set aside.
I will then focus on the process
of germ cell migration.
And then briefly, I will talk about
a few aspects of what happens actually
when these primordial germ cells
have to become germ line stem cells.
And then there are other lectures in these
series which talk about what actually
happens during oogenesis, and so
I'm leaving this out of my life cycle for