🚀 go-pugleaf

>In article <1989Oct31.034851.24494@agate.berkeley.edu>, mkkuhner@codon2.berkeley.edu (Mary K. Kuhner;335 Mulford) writes:
>> My favorite experiment showing the complexity of non-DNA information
>> in the cell was done with a protozoan which is covered with cilia,
>> all lined up the same way.  Very precise microsurgery was used to
>> cut a strip off of the cell wall and put it back in reverse.
>> Somehow the cell survives this, and ends up with a row of backwards
>> cilia.  All descendents of that cell have a similar row, because
>> the old cell's cilia are used as templates for the new arrangement.

In article <7111@cs.utexas.edu> turpin@cs.utexas.edu (Russell Turpin) writes:
>
>This would seem to imply that, at least for unicellular life,
>Lamarck was not entirely wrong.  
>
>Russell

Ah...This is an interesting one.  The Membrane people have often
used it as a case of information in a membrane.

But, the key to this positional information may lie
in the fact that each of those little cilia are secured to ("grow" out of)
a Basal Body (the same as a centriole in animal-cell mitotic spindles).
These replicate in an interesting fashion: During vegatative growth,
a new BB is built alongside the old one and the position (relative placment
and angle) of the new one to the old one is very precise.
In some ways, you could say the old BB is a template for the new one.
So, you would expect the reverse position of the cilia to be maintained
as a function of the placement of the BB.
However, it is important to point out that this alterred positional
information is NOT passed on through sexual reproduction.


People have argued for decades over whether BBs represent an endosymbiont.
To that end, there has been for decades a hunt for a genome associated
with BBs (as is the case for mitochondria and chloroplasts).
The history of this has some amusing highs and lows.

David Luck's group (Zenta Ramanis, Susan Dutcher etc.) at Rockefeller showed
that in Chlamydomonas there is a linkage group (called Fragment 2,
linkage-group 19, or ULG, for Uni Linkage Group--a few mutations on the
chromosome lead to cells with one flagellum, hence "uni").
All mutations that mapped to that group affected the basal-bodies and/or
the flagella.  This linkage group is seriously weird--it maps as
a circle but apparently isn't, recombination is temperature sensitive
(raise the temp and recomb. increases), it is apparently diploid
in the cell, but the genetics behave as a haploid, and, unlike other
organelle DNA, it is inherited in a Mendelian fashion.

The Oct. 6th issue of Cell has an article from Luck's group (Hall, Ramanis
and Luck), and a minireview on the topic (also the cover picture).
It seems they have good evidence that the genome IS associated
with the BB, and it is linear.  They did some RFLP mapping, cloned some
of it, and used the clone as a probe on Orthoganal-pulse gels (to
show it is a linear molecule of about 6 mb) and in sito hybridization (to
show localization to the BB).

So, Is it Lamarkian?  Well, yes, sort of.  The positional information
in the above example has nothing to do with altering the DNA
of the BB, so it is not a mutation. (If Hall's result holds up, I think it
is safe to refer to the DNA of Basal bodies.)
But, this is only propogated vegetatively.  All you get is a clonal
population derived from the original.  One might imagine other
cases where an acquired change is propogated during Fission-growth.
But I can't think of one (other than mutations to DNA, of course) that
is propogated sexually.  Since none the of species that lead to the
Darwinian and Lamarkian models reproduce by fission, one can hardly
expect Darwin's rules to account exactly fro that type of reproduction.

Interesting stuff.

-tony