Is timefor a cell a recurringevent or something continuous? Well to find the answer you mustfirst know its temperature
A RECENT piece of work by
Fen-Biao Gao and colleagues at University
College London shows that
oligodendrocytes, cells that
are responsible for the insulation that protects vertebrate nerve cells, do count
time but not in terms of the
number of cell divisions.
Earlier studies had
shown that when isolated
from the optic nerve of the
rat, the oligodendrocyte
precursor cells divided a
fixed number of times and
then stopped dividing and
proceeded to differentiate.
The present work, which
attempts to test when it is
that the cells know to stop
dividing is simple and ele-
gant. It rests on the observation that there is a critical
difference between what
happens at 37c, the normal body tem-
perature and 33'c. When cultured at
33'c, the precursor cells divide more
slowly than they do at 37c. However,
they stop dividing and begin to differentiate after significantly fewer divisions at 33oc thin at 37oc.
Speaking figuratively, the development of an embryo into an adult
involves the cells' knowing where they
are and what time it is. Depending on
their position in the embryo and on the
developmental stage they are at, particular groups of cells switch 'on' or 'off
different subsets of genes; and the products encoded by the genes determine the
entire diversity of shape, form and function - in short, the course of development. Much contemporary research
focuses on the question of exactly how
position and time are measured. Of the
two, position-sensing mechanisms have
received more attention.
As for timekeeping, there are two
attractive candidates out of a number of
possibilities. One is that cells use an
internal oscillator, something that
recurs with predictable regularity.
The most obvious process that
might qualify is cell division. Then the
number of 'ticks' of the clock, or
number of cell divisions in our example,
can be used to tell time. Another
possibility might be for cells to measure
time in a continuous fashion, as we
intuitively do when thinking of aging.
Unfortunately, the way the experiment was designed makes it difficult to
say exactly when the cells started differentiating (the percentage of differentiated cells was monitored after a
fixed number of days in culture).
Nevertheless, it is evident that whatever
the clock is - elapsed time is an obvious candidate - it cannot be based on
counting the number of cell divisions
(Current Biology, Vol 7).
We are a voice to you; you have been a support to us. Together we build journalism that is independent, credible and fearless. You can further help us by making a donation. This will mean a lot for our ability to bring you news, perspectives and analysis from the ground so that we can make change together.
Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.