Cell Nucleus Biogenesis, Structure and Function
423
insulators, which are believed to func-
tion as chromatin domain boundaries
that generate self-contained units of gene
expression.
The combined action of promoter, en-
hancer, S/MAR and insulator elements
will together dictate levels of gene expres-
sion. In addition, through their interaction
with proteins involved in gene expression,
these elements will play an important part
in determining how DNA is organized and
packaged within the nuclear space.
5
Overview
This chapter sets out to give the reader
an overview of our present understanding
of the nuclear structure and function.
The majority of examples have been
drawn from studies on mammalian cells.
This was a deliberate choice, as even
though many critical advances have been
made using simple model systems, the
added complexity of mammalian genomes
makes them a much more challenging
object of study. As the area covered herein
represents an extensive Feld of research, it
is inevitable that the treatment of many
has been superFcial. This should not
be seen to reflect my own view of the
relative importance of different topics.
Instead, I have attempted to deliver a
coherent appraisal of this cell organelle
with the intention of stimulating interest
i
nt
h
er
e
a
d
e
rs
ot
h
a
th
eo
rs
h
ew
i
l
l
feel encouraged to look deeper into this
fascinating subject.
In discussing the nucleus, the main fo-
cus of attention must be the structure and
function of DNA. Little attention is paid
to the DNA itself, though the way DNA
is packaged in nuclei undoubtedly has a
profound influence on chromatin func-
tion. The structure of chromatin and more
importantly the cellular mechanisms that
modulate chromatin fluidity and hence
control access of DNA to RNA and DNA
polymerases are now well known. Indeed,
histone modiFcations represent a major
source of epigenetic information that com-
plements the genetic information deFned
by DNA sequence. Chromosome structure
and global nuclear architecture provide
additional sources of epigenetic informa-
tion, which at least have the potential to
influence chromatin function. However,
while many speciFc examples have been
reported to show how chromosome and/or
nuclear location influence chromatin func-
tion, the relative importance of this type of
spatial epigenetics remains largely unex-
plored. Whatever the hierarchies of control
turn out to be, there is no denying that
the structure of mammalian nuclei and
the functions that they perform are very
sophisticated indeed.
See also
Chromosome Organization
within the Nucleus; Developmental
Cell Biology; Electron Microscopy
in Cell Biology.
Bibliography
General Reference and Books
Alberts, B.,
Johnson, A.,
Lewis, J.,
Raff, M.,
Roberts, K., Walter, P. (2002)
Molecular Biology
of the Cell
, 4th edition, Garland Publishing,
New York.
Cook, P.R. (2001)
The Principles of Nuclear
Structure and Function
, John Wiley and Sons,
New York.
Endow, S.A., Glover, D. (1998)
Dynamics of Cell
Division
, Oxford University Press, Oxford.
King, R.J.B. (2000)
Cancer Biology
, 2nd edition,
Prentice Hall, Harlow.
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