This topic of "epimutation" by means of "methylation" began to be a subject of discussions in the journal "Science" around the year 2000. In the following post to newsgroup talk.philosophy.misc, someone reprinted a couple of those exchanges that had appeared in the journal.
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Subject: Lamarck Could be Right?
Date: Fri, 26 May 2000 00:01:10 GMT
From:
[email protected]
Newsgroups: talk.philosophy.misc
On April 7 in "Science", the French science news correspondent, Michael
Balter, published the following article (the second paste). We found it
necessary to respond by submitting a letter to the editor (as yet
receipt not acknowledged). The full text of this letter " Lamarck and
Antibody Genes:" is pasted below (the first paste). An outline of our
argument for the general reader ("The Evidence for Lamarck") can be
found at the website of one of us (EJ Steele) appended to his contact
address.
Full text of letter to the editor of "Science" reads :
Lamarck and Antibody Genes
We read with interest the News Focus article (M. Balter "Was Lamarck
just a little bit right?" 7 April, 2000, page 38 in "Science" )
reviewing work on methylation-based epimutations which constitute a form
of Lamarckian transmission of acquired characters in animals and plants.
A role for these epigenetic phenomena in evolution was previously
outlined in 1994 in a book by Jablonka and Lamb (1). However, the
Balter article ignores the possibility that selected, adaptive changes
in gene sequences in somatic cells can be fed back to germ cells and
transmitted to progeny animals, thus contributing in a Lamarckian and
Darwinian manner to evolution. This concept, based upon evidence from
the immune system of vertebrates and feed back of reverse transcripts of
mutated antibody genes from lymphocytes to germ cells was first
elaborated over 20 years ago (2). Reports of uptake by mammalian sperm
of DNA and RNA and reverse transcriptase activity in sperm provide a
mechanism for movement of somatic gene sequences to the germ-line (3).
Data from the immune system consistent with somatic to germ cell
movement of antibody genes has been reviewed in the scientific
literature (4), in a book for non-specialist readers (5) and in brief
form in HMS Beagle (6).
Edward J Steele
Molecular Immunology & Evolution Laboratory
Department of Biological Sciences
University of Wollongong
Wollongong NSW 2522
AUSTRALIA
E-mail Address
[email protected]
Website : http://www.uow.edu.au/science/biol/tsteele.html
Robert V Blanden
Division of Immunology and Cell Biology
John Curtin School of Medical Research
Australian National University
Canberra 2601
AUSTRALIA
E-mail :
[email protected]
References
1. E. Jablonka and M. Lamb Epigenetic Inheritance and Evolution - The
Lamarckian Dimension . Oxford University Press. (1994).
2. E.J. Steele Somatic Selection and Adaptive Evolution : On the
Inheritance of Acquired Characters Williams-Wallace , Toronto (1979);
2nd Ed University of Chicago Press, Chicago (1981).
3. G. Zoraqi and C. Spadafora (1997) DNA Cell Biol 16: 291 - 300; R.
Giordanao et al (2000) J Cell Biol 148 : 1107-1114; and also see
independent experimental data in A.C. F. Perry et al (1999) Science 284
:
1180-1183.
4. R.V Blanden et al (1998) Immunol Rev 162 : 117-132.
5. E.J. Steele, R.A. Lindley and R.V. Blanden Lamarck's Signature: How
retrogenes are changing Darwin's natural selection paradigm. Perseus
Books, Reading, MT (1998).
6. E.J. Steele and R.V. Blanden (1999) "What is Lamarck's Signature?"
- in HMS Beagle at
http://www.biomednet.com/hmsbeagle/56/viewpts/ op_ed ,
and
http://www.biomednet.com/hmsbeagle/57/viewpts/ letters
----------------------------------------------------
GENETICS (Science vol 288 April 7, 2000, p. 38):
Was Lamarck Just a Little Bit Right?
Michael Balter
Pity poor Jean-Baptiste Lamarck. Today, he is remembered mostly for the
discredited theory that evolution occurs when parent organisms pass on
to their offspring characteristics they have acquired during their
lifetimes. But this French naturalist, who lived from 1744 to 1829, was
one of the great scientists of his age. He was the first to study
invertebrate animals systematically, and he was an early champion of the
idea that evolution rather than divine intervention was responsible for
changes in plants and animals over time. But by the early 20th century,
Lamarck's concept of evolution had been superceded by Darwin's theory of
natural selection and the genetic laws of Gregor Mendel. And since then
his name has become inextricably linked to that of his most notorious
disciple--the Stalin-era agronomist Trofim Lysenko--who forced Soviet
geneticists to accept Lamarckian ideas or be banned from doing research
(see main text). Recently, however, Lamarck's name has been creeping
back into the scientific literature. The reason: an explosion in the
field of epigenetics, the study of changes in genetic expression that
are not linked to alterations in DNA sequences. Some of these epigenetic
changes can be passed on to offspring in ways that appear to violate
Mendelian genetics. And although these new findings do not support
Lamarck's overall concept, they do raise the possibility that
"epimutations," as they are called, could play a role in evolution. "I
don't know of any evidence that Lamarck was even a little bit right, but
this is possible," says molecular geneticist Eric Selker of the
University of Oregon, Eugene. "It is increasingly clear that epigenetic
mechanisms play important, sometimes critical, roles in biology."
Epigenetic changes, which include the "silencing" of genes by such
biochemical tricks as attaching methyl groups to segments of DNA so they
will not be read by the cell's protein-making machinery, are involved in
a host of processes, including gene regulation, development, and even
cancer (Science, 15 October 1999, p. 481). Although these alterations in
gene expression can clearly be passed from mother to daughter cells--for
example, when a muscle cell divides into two or cancerous cells
proliferate to form a tumor--they are normally "erased" when the germ
cells, which give rise to the next generation, are formed. Yet evidence
is accumulating that sometimes the epimutations are not erased. This
phenomenon has been spotted in plants, fruit flies, and yeast. And the
first convincing case in mammals was reported in the November 1999 issue
of Nature Genetics by biochemist Emma Whitelaw at the University of
Sydney in Australia and co-workers in Scotland and the United States.
Whitelaw's team worked with an inbred strain of mice in which all are
genetically identical and so should look exactly the same. But the coat
colors of these mice varied wildly, ranging from yellow to mottled with
every combination in between. Moreover, the coat color of newborn mice
was highly influenced by the color of the mother, but not of the father:
A yellow mother had more yellow pups than mottled, and a mottled mother
had more mottled pups than yellow, violating Mendelian principles that
traits are randomly distributed during reproduction. The team found that
coat color apparently depends on the degree to which a stretch of
regulatory DNA just upstream from a gene controlling coat color, called
agouti, is methylated. This in turn depends on how much of this
methylation state, if any, has been transferred from the mother through
the germ line to its offspring. Azim Surani, a developmental geneticist
at the University of Cambridge in the United Kingdom, comments that the
germ cells are normally "a very efficient cleaning machine, which wipes
out many of these epigenetic modifications. ... The [Whitelaw] paper
shows there are exceptions to this rule." As for whether epimutations
could play an important role in evolution--that is, whether they, like
alterations in DNA sequence, could be favored by Darwinian natural
selection--Surani says this partly depends on whether they are fairly
common, compared to classic genetic mutations, or rare. Moreover, Surani
and other researchers say, the likelihood that epimutations acquired by
adult organisms will be passed on to their offspring is limited by the
fact that in most animals the germ cells are segregated very early in
life. In mammals, the germ cells are formed and migrate to the embryonic
ovaries and testes long before the fetus is born, presumably shielding
them from epigenetic modifications in the adult. But the situation might
be different in plants, which produce their germ cells much later in
their life cycle. In the 9 September 1999 issue of Nature, molecular
geneticist Enrico Coen and colleagues at the John Innes Centre in
Norwich, U.K., reported that a mutant version of the toadflax plant
(Linaria vulgaris)--which results in flowers with radial rather than
bilateral symmetry--is due to an epimutation. In the mutant plant, a
gene called Lcyc is extensively methylated and thus not expressed--and
this methylated state is heritable by subsequent generations of toadflax
plants. Coen and his colleagues conclude that such epimutations might
have both short- and long-term effects on plant evolution, both in
their own right and because methylated genes are more susceptible to
classic mutations that alter DNA sequences. Coen points out that Darwin,
like Lamarck, believed that the inheritance of acquired characteristics
played a role in evolution. The main difference between them was that
Lamarck thought evolution was driven by an organism's inner need to
adapt to its environment, such as in the famous example of the giraffes
who stretched to reach the upper branches of trees and then passed on
the phenotypic trait for longer necks to their progeny. Darwin, on the
other hand, posited that natural selection of genetic alterations,
rather than some "inner striving," drives adaptive changes. Coen
cautions that although the new studies of epimutations challenge the
dogma "that the only heritable mutations of significance are caused by
DNA sequence changes," they offer no support at all for the idea that
morphological changes acquired during the lifetime of an adult organism
can be inherited in the Lamarckian sense. But some researchers say that
the new research does suggest a potential mechanism for how epigenetic
changes could play an adaptive role. "Although it would be stretching it
to regard epigenetic traits as adaptations comparable to Lamarck's view
of how the giraffe acquired its long neck," comments Selker, "we do know
that environmental factors, such as temperature, can influence
epigenetic marks such as methylation." And one thing seems sure: The
explosion in epigenetic research has helped restore Lamarck to his
rightful place in scientific history, even if he did get the big picture
wrong. Says Coen: "Lamarck was a true pioneer of evolutionary theory."
Related articles in Science:
GENETICS:
Uphill Battle to Honor Monk Who Demystified Heredity.
Robert Koenig
Science 2000 288: 37-39. (in News Focus) [Summary] [Full Text]
Volume 288, Number 5463 Issue of 7 Apr 2000, p 38
©2000 by The American Association for the Advancement of Science.