So, epigenetic control isn't just important in the differentiation of the
three cell types we spoke about in the last lecture, but in fact, it's important
throughout development. And this is consistent with the idea that
I mentioned that epigenetic marks demarcate the beginnings and the ends of
chromosomes and the middle of chromosomes. So, because epigenetic control is
important in chromosome structure, as well as in the control of gene
expression, of course, that's important for every cell type.
So, here I'm showing you in this diagram that epigenetic control is important
throughout development, from the single cell fertilised egg, or otherwise known as
the zygote. Through pre-implantation development.
So, this is before the embryo has actually implanted into the uterus to
make a placenta. Post implantation development, this
strange looking embryo here, through mid gestation development.
The development of many different cell types in the adult.
For example here, showing the blood cell system.
and even through to the generation of the sperm and the eggs.
Particular epigenetic marks are very important in this case, because these
highly specialised structures, the sperm and the egg require a unique set of
epigenetic marks to be able to allow their particular functions.
So, these epigenetic marks are laid down throughout development and this
helps to ensure, to specify cellular identity, and for that cellular identity
to be maintained. But in addition, these marks need to be
removed between development. And that's why there's this break in the
arrow here, to indicate that they're removed between generations to ensure
totipotency for the next generation. So, as you might expect then for this
ubiquitously important process of epigenetic control.
When it goes wrong, it results in a wide array of different disorders and
some of these we'll cover in later lectures.
For example, the imprinting disorders, and these result of epigenetic control
goes wrong in either the gametes or in early development.
Abhorrent epigenetic control can result in early embryonic lethality, slightly later
early embryonic lethality if the placenta fails, and it can result in many
different types of tumours. So for example, germ cell tumours, so
these are the ones for example, found in the ovary, where an oocyte will generate a
tumour. And because of its ability to be able to
make many different cell types when fertilised by a sperm, a tumour derived from these
cells can actually have many different cell types in there as well.
And tumour genesis in the adult of many different kinds, so for example leukaemia is
found in the blood system, skin cancer, breast cancer, colon cancer, any cancer
that you can think of has epigenetic abnormalities.
And we're going to spend some time thinking about this in later lectures.
Abhorrent epigenetic control or epigenetic mistakes are also found and
result in blocks of differentiation. What I mean here is that, a cell that is
a precursor cell for example, of a B cell may not be able to actually make a mature
B cell, cannot continue to progress through to make a mature B cell
And instead, gets stuck at a earlier
stage, if there are some epigenetic abnormalities.
And finally, if you don't have appropriate epigenetic control in the egg
and the sperm, this results in infertility.