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0:00
I am Barbara Migeon,
a member of the McKusick
Nathans Institute
of Genetic Medicine
at Johns Hopkins.
The title of my talk
is X Chromosome Inactivation
in Human Cell.
0:15
I will talk to you
about X chromosome inactivation,
the way mammals carry out
X dosage compensation.
This has been
the subject of previous talks
by Mary Lyon and Jenny Graves.
Although we hear a lot
about how the mouse
inactivates one X chromosome,
I will be talking
about the version
of X chromosome inactivation
in our own species.
First I will tell you
what we know
from studies of human cells
and human subjects.
Then I will talk about
how inactivating
human X chromosomes differ
from the process
in other species
and what might be responsible
for such differences.
And last, changing the focus
from inactive to active X,
I will tell you
why diploid human cells
have only a single active X,
no matter the number of Xs
in the cell
and how this active X is chosen.
1:17
Most studies of the early events
in X inactivation
have been carried out in mice
as it's been difficult to look
at human embryos at that time.
However, the study of humans
has other advantages.
Our phenotype is understood
better than that
of any other organism
and we can learn a good deal
from the study of cultured cell.
Also one X chromosome
can be isolated from the other
in hybrid cell.
Spontaneous abortions provide
a wealth
of X chromosome deletions
and different numbers
of X chromosome.
And now we have begun
to study human ES cells,
embryonic stem cells
and cleaving embryos left over
from in vitro fertilization.
We can also transfect
human genes into mice
for developmental study.
Furthermore, the fact
that humans are not inbred
and are in fact
very heterozygous
for many X-linked genes
has enabled studies
less feasible in other mammal.
Females are indeed
a genetic mosaic
as you see here,
with some cells expressing
the genes from their paternal X,
and others,
the genes from the maternal one.
