This is an old one
that I dredged up from 2006: it never got used then, and I am trying to establish a backlog for while I go travelling, and i imagine it is now somewhat dated, but i may get one reader to run and find out. Please take that into account.
Sam Weller in Pickwick
Papers spoke of the problems of seeing. "If they was a pair o' patent
double million magnifyin' gas microscopes of hextra power, p'raps I might be
able to see through a flight o' stairs and a deal door, but bein' only eyes,
you see, my wision's limited", he declared.
As an undergraduate, I
often wished we had one of Sam's microscopes, so we could look at genes, and
see what the chromosomes did. This was at a time when the genetic code was just
beginning to be decoded, long before anybody would think of sequencing a genome
for a Ph D — something that can be done in 24 hours, these days.
The advances have been
magnificent, but until now, there has been no sign that the equivalent of Sam's
dreamt-of unlimited wision has escaped us. Nobody has been too surprised,
because a bit of simple physics will tell you that the idea is ridiculous. Impossible,
say the older and more experienced scientists.
Somebody, I think it
was probably Asimov, once said something along the lines of, "If an old,
respected scientist tells you something is possible, he's almost
certainly right. But if an old, respected scientist tells you something is impossible,
he's very likely wrong." These days, of course, we would have to eschew
the gender-specific language that marks this as an old adage — but could this
old adage be right?
Quite probably, where
Sam's microscope is concerned. In the August 31 (2006!) issue of Nature,
there was a story about using multiphoton fluorescence microscopy to watch
chromosomes change their form in order to activate their genes to synthesize
key proteins in fruit fly cells.
Jie Yao used MPM to
make images living salivary gland tissue of Drosophila (fruit flies). Now
that takes me back 40 years to crisp autumn and winter mornings in an
east-facing lab, where one ripped the heads off fruit fly grubs to drag out the
salivary glands, which contain massively multistranded chromosomes. These were
then placed on a slide, squashed and marinated in acetic orcein — to this day,
the smell of vinegar takes me back to that time.
Proust had his petites
madeleines, I have maggot innards in vinegar to switch on my recollections.
That is probably the least elegant contrast of the two cultures that I have
ever penned before breakfast, but that's how it is, or was.
Unlike other methods,
which lack penetrating power and can damage the specimen, MPM delivers crisp,
clear images, even in thicker tissue samples like Drosophila salivary
glands, and from here, I will rely more heavily in the account I have had from
Cornell.
Whenever a cell is
stressed it produces proteins that help the cell resist stress. The process is
triggered by a molecule called heat shock factor (HSF), which interacts with
genes to cue the synthesis of new proteins, but this well-known process had
never been seen in living cells.
The polytene cells in
the salivary glands, with their giant, multistranded chromosomes, have hundreds
of sets of the genome instead of the usual two sets in conventional cells. This
enlarges the usual nuclear dimensions by about 10 times, making them large
enough to image the detail — which is why we used to squash and stain them four
decades back. They are still worth looking at.
The results were
stunning. "Within two weeks we had spectacular pictures," says
Professor John Lis, Jie Yao's supervisor. The images included pictures of the
genes (hsp70 genes) that protect flies from the effects of extreme heat. By
cranking up the heat, the researchers could activate these genes, and by using
fruit flies specifically bred to carry fluorescent proteins on HSF, they could
watch the transcription factors in action.
"This is the first
time ever that anyone has been able to see in detail, at native genes in vivo,
how a transcription factor is turned on, and how it then is activated,"
says Watt Webb.
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