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0:00
Hello.
My name is Janet Rossant.
I'm a senior scientist at the
Hospital for Sick Children
in Toronto and
Professor of Molecular
Genetics at the
University of Toronto.
This talk is going to
be about stem cells
from the early mammalian embryo.
0:15
Early mammalian development is
the stage of development of which
the zygote, a single fertilized egg,
develops through to the blastocyst.
The blastocyst is the
stage of development
from which we can derive
embryonic stem cells.
And as I'll show you
later, in the mouse
we can also derive other stem
cells that represent some
of the extra embryonic lineages
that a mammalian embryo
uses to survive in the uterus.
If we look at the stages of
mouse development shown here,
these stages from a single cell
to the blastocyst take four days.
And we see that the embryo undergoes
a process known as cleavage
in which the cells
continue to divide,
but don't specialize until
it begins to cavitate to form
a blastocyst with three
distinct cell types.
The outer, trophectoderm, enclosing
a group of cells at one end
called the inner cell
mass, which then go on
to form epiblast and
the primitive endoderm.
1:10
In this slide, we see some
real images of mouse embryos
during these stages of
preimplantation development.
And in fact, these images go
right back to the oocyte stage
through to the blastocyst.
We see a process where the oocyte
matures, fertilization occurs
to form the zygote, and then the
embryo starts to undergo cleavage.
All of these embryos are shown
without their encompassing zona
pellucida, which is
kind of an egg shell
that protects the embryo
in the uterine environment.
However, it allows us to
see the cells very clearly.
The next event that occurs around
a two-cell to four-cell stage
is a process of genome
activation where
the zygote genome becomes active.
The embryo continues to divide
and undergoes a process called
compaction at the
8- to 16-cell stage
where instead of seeing these
single cells we now have something
that's called a morula
where all the cells are
very compacted against each other.
As we will see later, this
is a very important event
as it starts to establish
an inside environment
and an outside
environment leading up
to the formation of the blastocyst.
