[Paleopsych] FW: RE:The likely Meta-System in Junk DNA
HowlBloom at aol.com
HowlBloom at aol.com
Sun Nov 28 07:52:57 UTC 2004
Hb: The material forwarded below by Joel Isaacson is amazing.
But can I gloat for a minute? You’ll find the bulk of these ideas proposed
in paleopsych discussions that go back to at least 2001. Not the RNA
mechanisms--a huge part of the puzzle--but the general idea that junk dna provides the
instructions for putting together the protein leggo blocks of complex
creatures, and for changing the arrangement of those blocks over time.
The prime contributors to this thread have been Greg Bear, Eshel Ben-Jacob,
and, ummm, this is gonna be obnoxious, me.
Below is the Scientific American article that Joel Isaacson, Shann Turnbull,
and Cliff Joslyn are referring to. A special thanks to Cliff for summing the
material and its significance up so exquisitely. Howard
In a message dated 11/27/2004 5:50:53 PM Eastern Standard Time,
isaacsonj at hotmail.com writes:
>From: "Shann Turnbull" <sturnbull at mba1963.hbs.edu>
>Reply-To: pcp-discuss at lanl.gov
>To: <pcp-discuss at lanl.gov>
>CC: <vturchin at bellatlantic.net>
>Subject: RE: [pcp-discuss:] The likely Meta-System Transition in molecular
>evolution
>Date: Sat, 27 Nov 2004 17:45:44 +1100
>
>I also found the Mattick article exciting, but not being a biologist is was
>not because that it challenged our thinking about the role of DNA but
>because it indicated how the strategies found in nature for building
>complex
>self-reproducing organisations might provide guidance on how to design
>complex social organisations and perhaps even a "global brain".
>
>It showed the need for an interdisciplinary approach to progress insights
>into all the disciplines involved.
>
>Regards
>
>Shann
>
>Shann Turnbull PhD http://www.aprim.net/associates/turnbull.htm
>Principal, International Institute for Self-governance
>PO Box 266 Woollahra, Sydney, Australia 1350
>Ph+612 9328 7466 Mobile 0418 222 378, Papers at:
>http://ssrn.com/author=26239
>
>
>-----Original Message-----
>From: owner-pcp-discuss at maillist.lanl.gov
>[mailto:owner-pcp-discuss at maillist.lanl.gov] On Behalf Of Cliff Joslyn
>Sent: Saturday, 27 November 2004 4:28 PM
>To: pcp-discuss at lanl.gov
>Cc: vturchin at bellatlantic.net
>Subject: [pcp-discuss:] The likely Meta-System Transition in molecular
>evolution
>
>I would like to draw everyone's attention to:
>
>Mattick, John: (2004) ``The Hidden Genetic Program of Complex
>Organisms'', Scientific American, v. 291:4, pp. 60-67
>
>See also his technical papers:
>
>"The evolution of controlled multitasked gene networks: The role of
>introns and other noncoding RNAs in the development of complex
>organisms", Mattick, JS; Gagen, MJ Source: Molecular Biology and
>Evolution; September, 2001; v.18, no.9, p.1611-1630
>
>"Challenging the dogma: The hidden layer of non-protein-coding RNAs in
>complex organisms." Mattick, JS Source: BioEssays; October 2003;
>v.25, no.10, p.930-939
>
>"RNA regulation: a new genetics?" Mattick, JS Source: NATURE REVIEWS
>GENETICS; APR 2004; v.5, no.4, p.316-323
>
>I saw Mattick give a technical plenary at the 2003 Intelligence
>Systems for Molecular Biology (ISMB 03, one of the two premier
>bioinformatics conferences), and was really blown away. The Scientific
>American article is a superb semi-technical distillation of his
>work. He has a revolutionary, but simple and elegant, thesis, highly
>coherent with the principles of evolutionary cybernetics, and most
>importantly, highly likely to be TRUE, about molecular evolution. It
>puts so much of what I know about biological systems in context, while
>answering many current mysteries, and really opens up the kind of
>explanatory paradigm we've been lacking for so long, but is so
>obviously suggested by a cybernetic perspective.
>
>In brief, consider these facts:
>
>*) Most genomes are characterized by a VERY high degree (> 98%) of
>genomic sequence which are not genes, that is, does not code for
>protein. This includes introns and so-called "intergenic space".
>
>*) However, recent evidence indicates that much of this genome is
>actually expressed as RNA, and moreover, good chunks of it are
>identical among evolutionarily distinct orgnanisms. This is a property
>called "conservation", which indicates that it's functionally
>significant for survival. And moreover, portions of non-coding DNA are
>MORE highly conserved than proteins.
>
>*) This is NOT true in prokaryotes (bacteria lacking nuclei), but is
>in eukaryotes. Prokaryotes were the only life on earth for 2.5 B
>years. But a few hundred million years after the emergence of
>eukaryotes also saw the origin of metazoans (multi-cellular
>organisms), all of which are eukaryotes.
>
>*) Nonetheless, prokaryotes have on the same order of magnitude of
>number of genes as eukaryotes. The riddle that organismal size and
>complexity (however measured, a different discussion) does not
>correlate to the number of genes present is well noted, especially in
>the wake of the genomic revolution.
>
>*) BUT, total genome size, and in particular the RATIO of non-coding
>to coding genome DOES more or less correlate with complexity.
>
>*) Finally, we note that the standard hypothesis for explaining
>regulatory organization of sufficient complexity to generate metazoans
>is that it is somehow embedded in the combinatorics of protein
>interaction, that is, proteins acting on each other to form regulatory
>networks. This is despite the fact that to a first approximation,
>regulatory complexity must grow non-linearally with the number of
>"components" controlled, on the order of the quadratic (to handle
>pairs of proteins). And indeed, in PROKARYOTES the number of genes
>increases with the square of organism size, up to a limit where the
>number of regulatory genes is predicted to exceed the number of
>functional genes, and the plateaus.
>
>The conclusion is inescapable: there was a major evolutionary step at
>2.5 B years where an RNA-mediated network for the regulation of
>protein function, encoded in "non-coding" DNA (introns and
>intergenic space), arose, which resulted in the possibility of complex
>organisms, including eukaryotes and especially the morphological
>development of, and cell differentiation within, metazoans. Mattick
>uses the metaphor of genes as simply the "parts list" (a description
>of the individual TYPES of "lego blocks"), and the rest as the
>instructions for putting them together (how many blocks of which type
>to use where and when in morphological development).
>
>The argument is so strong and so reasonable, and simply MUST be
>accepted prima facie: "The implications of this rule are
>staggering. We may have totally misunderstood the nature of the
>genomic programming and the basis of variations in traits among
>individuals and species." (Mattick, the Sci Am paper).
>
>There's much more to this argument, including some fascinating
>observations about further GENETIC specialty of primates, and even
>humans. And while I've seen one of Mattick's technical talks, and read
>the Sci Am piece, I have not studied his papers. Nor am I anything
>like an expert in this area. My good colleagues here at LANL who are
>molecular biologists say "yes, he's made a splash, but let's go slow".
>And of course revolutionary ideas require the strongest evidence, and
>Mattick is suggesting nothing other than a major revision to, if not
>an obliteration of, the Central Dogma:
>
>"We may be witnessing such a turning point in our understanding of
>genetic information. The central dogma of molecular biology for the
>past half a century and more has stated that genetic information
>encoded in DNA is transcribed as intermediary molecules of RNA, which
>are in turn translated into the amino acid sequences that make up
>proteins. The prevailing assumption, embodied in the credo 'one gene,
>one protein', has been that genes are generally synonymous with
>proteins. A corollary has been that proteins, in addition to their
>structural and enzymatic roles in cells, must be the primary agents
>for regulating the expression, or activation, of genes." (Mattick,
>the Sci Am paper).
>
>But fortunately, I'm not a biologist, and so I can without hesitancy
>say the following to this group of people interested in (and some
>dedicated to) Turchin's Meta-System Transition (MST) theory.
>
>Turchin's original evolutionary system begins with multi-cellular
>organisms, and we have speculated for some time about extending the
>ideas to earlier evolutionary times. The route is now open with the
>origin of the control of genetic expression. In the MST schema, this
>is "X is the control of genetic expression", and I don't really know
>what X is, something like "protein mechanisms" or "protein
>interaction". But the other hallmarks of am MST are there, in the
>possible divergence and specialization of the components being
>controlled.
>-----
>O---------------------------------------------------------------------------
> >
>| Cliff Joslyn, Research Team Leader (Cybernetician at Large)
>| Knowledge Systems & Computational Biology; Computer & Computational
>Science
>| Los Alamos National Laboratory, Mail Stop B265, Los Alamos NM 87545 USA
>| joslyn at lanl.gov http://www.c3.lanl.gov/~joslyn (505) 667-9096
>V All the world is biscuit-shaped. . .
________
Retrieved November 28, 2004, from the World Wide Web NEW YORK PUBLIC
LIBRARY-MID MANHATTAN Title: THE HIDDEN GENETIC PROGRAM of COMPLEX ORGANISMS , By:
Mattick, John S., Scientific American, 00368733, Oct2004, Vol. 291, Issue 4
Database: Academic Search Premier THE HIDDEN GENETIC PROGRAM of COMPLEX
ORGANISMS Contents Overview/Revising Genetic Dogma The Ubiquitous Junk From Parasites
to Parallel Controls Regulating Development Controlling Complexity MORE TO
EXPLORE Biologists assumed that proteins alone regulate the genes of humans and
other complex organisms. But an overlooked regulator based on RNA may hold
the keys to development and evolution Overview/Revising Genetic Dogma * A
perplexingly large portion of the DNA of complex organisms (eukaryotes) seems
irrelevant to the production of proteins. For years, molecular biologists have
assumed this extra material was evolutionary "junk". * New evidence suggests,
however, that this junk DNA may encode RNA molecules that perform a variety of
regulatory functions. The genetic mechanisms of eukaryotes may therefore be
radically different from those of simple cells [prokaryotes]. * This new theory
could explain why the structural and developmental complexity of organisms does
not parallel their numbers of protein-coding genes. It also carries important
implications for future pharmaceutical and medical research. Assumptions can
be dangerous, especially in science. They usually start as the most plausible
or comfortable interpretation of the available facts. But when their truth
cannot be immediately tested and their flaws are not obvious, assumptions often
graduate to articles of faith, and new observations are forced to fit them.
Eventually, if the volume of troublesome information becomes unsustainable, the
orthodoxy must collapse. We may be witnessing such a turning point in our
understanding of genetic information. The central dogma of molecular biology for
the past half a century and more has stated that genetic information encoded in
DNA is transcribed as intermediary molecules of RNA, which are in turn
translated into the amino acid sequences that make up proteins. The prevailing
assumption, embodied in the credo "one gene, one protein," has been that genes are
generally synonymous with proteins. A corollary has been that proteins, in
addition to their structural and enzymatic roles in cells, must be the primary
agents for regulating the expression, or activation, of genes. This conclusion
derived from studies primarily on bacteria such as Escherichia coli and other
prokaryotes (simple one-celled organisms lacking a nucleus). And indeed, it is
still essentially correct for prokaryotes. Their DNA consists almost entirely
of genes encoding proteins, separated by flanking sequences that regulate the
expression of the adjacent genes. (A few genes that encode RNAs with
regulatory jobs are also present, but they make up only a tiny fraction of most
prokaryotes' genetic ensembles, or genomes.) Researchers have also long assumed that
proteins similarly represent and control all the genetic information in
animals, plants and fungi--the multicellular organisms classified as eukaryotes
(having cells that contain nuclei). Pioneering biologist Jacques Monod summarized
the universality of the central dogma as "What was true for E. coli would be
true for the elephant." Monod was only partly right. A growing library of
results reveals that the central dogma is woefully incomplete for describing the
molecular biology of eukaryotes. Proteins do play a role in the regulation of
eukaryotic gene expression, yet a hidden, parallel regulatory System
consisting of RNA that acts directly on DNA, RNAs and proteins is also at work. This
overlooked RNA-signaling network may be what allows humans, for example, to
achieve structural complexity far beyond anything seen in the unicellular world.
Some molecular biologists are skeptical or even antagonistic toward these
unorthodox ideas. But the theory may answer some long-standing riddles of
development and evolution and holds great implications for gene-based medicine and
pharmaceuticals. Moreover, the recent discovery of this system affords insights
that could revolutionize designs for complex programmed systems of all kinds,
cybernetic as well as biological. The Ubiquitous Junk A DISCOVERY in 1977
presaged that something might be wrong with the established view of genomic
programming. Phillip A. Sharp of the Massachusetts Institute of Technology and
Richard J. Roberts of New England Biolabs, Inc., and their respective colleagues
independently showed that the genes of eukaryotes are not contiguous blocks of
protein-coding sequences. Rather they are mosaics of "exons" (DNA sequences
that encode fragments of proteins) interspersed with often vast tracts of
intervening sequences, or "introns," that do not code for protein. In the nucleus, a
gene is first copied in its totality as a primary RNA transcript; then a
process called splicing removes the intronic RNAs and reconstitutes a continuous
coding sequence-messenger RNA, or mRNA-for translation as protein in the
cytoplasm. The excised intronic RNA, serving no apparent purpose, has been presumed
to be degraded and recycled. But if introns do not code for protein, then why
are they ubiquitous among eukaryotes yet absent in prokaryotes? Although
introns constitute 95 percent or more of the average protein-coding gene in humans,
most molecular biologists have considered them to be evolutionary leftovers,
or junk. Introns were rationalized as ancient remnants of a time before
cellular life evolved, when fragments of protein-coding information crudely
assembled into the first genes. Perhaps introns had survived in complex organisms
because they had an incidental usefulness-for example, making it easier to
reshuffle segments of proteins into useful new combinations during evolution.
Similarly, biologists have assumed that the absence of introns from prokaryotes was a
consequence of intense competitive pressures in the microbial environment:
evolution had pruned away the introns as deadweight. One observation that made
it easier to dismiss introns--and other seemingly useless "intergenic" DNA
that sat between genes--as junk was that the amount of DNA in a genome does not
correlate well with the organism's complexity. Some amphibians, for example,
have more than five times as much DNA as mammals do, and astonishingly, some
amoebae have 1,000 times more. For decades, researchers assumed that the
underlying number of protein-coding genes in these organisms correlated much better
with complexity but that the relationship was lost against the variable
background clutter of introns and other junk sequences. But investigators have since
sequenced the genomes of diverse species, and it has become abundantly clear
that the correlation between numbers of conventional genes and complexity truly
is poor. The simple nematode worm Caenorhabditis elegans (made up of only
about 1,000 cells) has about 19,000 protein-coding genes, almost 50 percent more
than insects (13,500) and nearly as many as humans (around 25,000).
Conversely, the relation between the amount of nonprotein-coding DNA sequences and
organism complexity is more consistent. Put simply, the conundrum is this: less
than 1.5 percent of the human genome encodes proteins, but most of it is
transcribed into RNA. Either the human genome (and that of other complex organisms)
is replete with useless transcription, or these nonprotein-coding RNAs fulfill
some unexpected function. This line of argument and considerable other
experimental evidence suggest that many genes in complex organisms-perhaps even the
majority of genes in mammals--do not encode protein but instead give rise to
RNAs with direct regulatory functions [see "The Hidden Genome," by W. Wayt
Gibbs, SCIENTIFIC AMERICAN, November and December 2003]. These RNAs may be
transmitting a level of information that is crucial, particularly to development, and
that plays a pivotal role in evolution. From Parasites to Parallel Controls
THE CLUE to understanding this point may lie in a new interpretation of
introns. Contrary to early assumptions that introns generally date back to the dawn
of life, evidence amassed more recently indicates that these sequences invaded
the genes of higher organisms late in evolution. Most likely, they derived
from a type of self-splicing mobile genetic element similar to what are now
called group II introns. These elements are parasitic bits of DNA that have the
peculiar ability to insert themselves into host genomes and to splice themselves
out when expressed as RNA. Group II introns are found only occasionally in
bacteria, and it is easy to see why. Because bacteria lack a nucleus,
transcription and translation occur together: RNA is translated into protein almost as
fast as it is transcribed from DNA. There is no time for intronic RNA to
splice itself out of the protein coding RNA in which it sits, so an intron would in
most cases disable the gene it inhabits, with harmful consequences for the
host bacterium. In eukaryotes, transcription occurs in the nucleus and
translation in the cytoplasm, a separation that opens a window of opportunity for the
intron RNA to excise itself. Introns can thus be more easily tolerated in
eukaryotes. Of course, as long as introns needed to splice themselves in and out
of genomes, their sequences could not have deviated much from that of group II
introns. But a further leap in intron evolution may have accompanied the
evolution in eukaryotes of the structure called the spliceosome. This is a complex
of small catalytic RNAS and many proteins; its job is to snip intron RNA out
of messenger RNA precursors efficiently. By freeing introns from the need to
splice themselves, the spliceosome would in effect have encouraged introns to
proliferate, mutate and evolve. Any random mutation in an intron that proved
beneficial to the host organism would have been retained by natural selection.
Intronic RNAs would therefore be evolving independently and in parallel with
proteins. In short, the entry of introns into eukaryotes may have initiated an
explosive new round of molecular evolution, based on RNA rather than protein.
Instead of being junky molecular relics, introns could have progressively
acquired genetic functions mediated by RNA. If this hypothesis is true, its
meaning may be profound. Eukaryotes (especially the more complex ones) may have
developed a genetic operating system and regulatory networks that are far more
sophisticated than those of prokaryotes: RNAs and proteins could communicate
regulatory information in parallel. Such an arrangement would resemble the advanced
information-processing systems supporting network controls in computers and
the brain. Functional jobs in cells routinely belong to proteins because they
have great chemical and structural diversity. Yet RNA has an advantage over
proteins for transmitting information and regulating activities involving the
genome itself: RNAs can encode short, sequence-specific signals as a kind of
bit string or zip code. These embedded codes can direct RNA molecules precisely
to receptive targets in other RNAs and DNA. The RNA-RNA and RNA-DNA
interactions could in turn create structures that recruit proteins to convert the
signals to actions. The bit string of addressing information in the RNA gives this
system the power of tremendous precision, just as the binary bit strings used
by digital computers do. It is not too much of a stretch to say that this RNA
regulatory system would be largely digital in nature. The evidence for a
widespread RNA-based regulatory system is strong, albeit still patchy. If such a
system exists, one would expect that many genes might have evolved solely to
express RNA signals as higher-order regulators in the network. That appears to
be the case: thousands of RNAs that never get translated into protein
(noncoding RNAs) have been identified in recent analyses of transcription in mammals.
At least half and possibly more than three quarters of all RNA transcripts fit
this category. One would also expect that many of these RNAs might be
processed into smaller signals capable of addressing targets in the network. Hundreds
of "microRNAs" derived from introns and larger nonprotein-coding RNA
transcripts have in fact already been identified in plants, animals and fungi. Many of
them control the timing of processes that occur during development, such as
stem cell maintenance, cell proliferation, and apoptosis (the so-called
programmed cell death that remodels tissues). Many more such small RNAs surely await
discovery. These RNA signals, by finding targets on other RNAs, DNA and
proteins, could influence a cell's genetic program in many ways. For example, they
could inform various genes that a particular protein-coding sequence has been
transcribed, and that feedback could trigger a host of parallel adjustments.
More important, however, the RNA signals could serve as a powerful feed-forward
program embedded in the genetic material that controls the trajectories of
gene expression. If so, they could explain some of the deep mysteries
surrounding cell differentiation and organism development. Regulating Development
CONSIDER WHAT HAPPENS during human embryonic development: a single fertilized cell
progresses to become a precisely structured, beautifully sculptured organism
of an estimated 100 trillion cells with distinct positions and functions. The
pattern of gene expression that makes this transformation possible relies
heavily on two phenomena: modification of chromatin and alternative splicing.
Chromatin is the material that makes up chromosomes; it consists of DNA complexed
with proteins. Within cells, small chemical tags (such as methyl and acetyl
groups) can attach to segments of the DNA and to the chromatin proteins and
thereby determine whether the genes in the associated DNA will be accessible for
transcription or will stay silent. Recent results indicate that RNA signaling
directs the tagging of the chromatin and thus gene expression. Indeed, a number
of complex chromosomal processes, such as mitosis (cell division) and meiosis
(the formation of sperm and egg precursors), as well as a range of complex
genetic phenomena appear to depend on biochemical pathways that affect RNA
processing. Alternative splicing generates divergent repertoires of RNAs and
proteins in the cells of a body's different tissues, all of which share a common
set of genes. Most protein-coding transcripts are alternatively spliced in
mammals. When intron RNA is spliced out of a gene's transcript, the protein-coding
RNA regions may be assembled in more than one way to yield more than one type
of protein. The phenomenon is of fundamental importance to animal and plant
development, but no one yet understands how cells specify which form of a
protein they will make. Few protein factors that control the alternative splicing of
specific genes have been found. Consequently, researchers have usually
supposed that subtle combinations of general factors activate or repress alternative
splicing in different contexts. But no strong evidence has backed up that
presumption. A more likely and mechanistically appealing possibility, however,
is that RNAs regulate the process directly. In principle, these molecules could
exert exquisitely flexible control by tagging or grabbing particular
sequences in primary gene transcripts and steering how the spliceosome joins the
pieces. In keeping with that idea, DNA sequences at the intron-exon junctions where
alternative splicing occurs are often resistant to change during evolution.
Also, a number of laboratories have demonstrated that artificial antisense RNAs
designed to bind to such sites can modify splicing patterns in cultured
cells, as well as in whole animals. It is perfectly plausible that this phenomenon
occurs naturally in vivo, too, but has just not yet been detected. Controlling
Complexity SUCH CONSIDERATIONS lead naturally to a more general
consideration of what type of information, and how much of it, might be required to
program the development of complex organisms. The creation of complex objects,
whether houses or horses, demands two kinds of specifications: one for the
components and one for the system that guides their assembly. (To build a house, one
must specify the needed bricks, boards and beams, but one must also have an
architectural plan to show how they fit together.) In biology, unlike
engineering, both types of information are encoded within one program, the DNA. The
component molecules that make up different organisms (both at the individual and
the species levels) are fundamentally alike: around 99 percent of the proteins
in humans have recognizable equivalents in mice, and vice versa; many of those
proteins are also conserved in other animals, and those involved in basic
cellular processes are conserved in all eukaryotes. Thus, the differences in
animals' forms surely arise more fundamentally from differences in the
architectural information. Protein-coding genes obviously specify the components of
organisms, but where does the architectural information reside? Biologists have
widely assumed that the instructions for assembling complex organisms are
somehow embedded in the diverse combinations of regulatory factors within
cells--that is, in the permutations of regulatory proteins interacting with one another
and with the DNA and RNA. Yet, as Daniel C. Dennett of Tufts University has
observed, although such combinatorics can generate almost endless possibilities,
the vast majority will be chaotic and meaningless-which is problematic for
biology. Throughout their evolution and development, organisms must navigate
precise developmental pathways that are sensible and competitive, or else they
die. Generating complexity is easy; controlling it is not. The latter requires
an enormous amount of regulatory information. Both intuitive and mathematical
considerations suggest that the amount of regulation must increase as a
nonlinear (usually quadratic) function of the number of genes. So, as the system
becomes more complex, an increasing proportion of it must be devoted to
regulation. This nonlinear relation between regulation and function appears to be a
feature of all integrally organized systems. Therefore, all such systems have an
intrinsic complexity limit imposed by the accelerating growth of their control
architecture, until or unless the regulatory mechanism changes fundamentally.
In agreement with this prediction, the number of protein regulators in
prokaryotes has been found to increase quadratically with genome size. Moreover,
extrapolation indicates that the point at which the number of new regulators is
predicted to exceed the number of new functional genes is close to the
observed upper limit of bacterial genome sizes. Throughout evolution, therefore, the
complexity of prokaryotes may have been limited by genetic regulatory
overhead, rather than by environmental or biochemical factors as has been commonly
assumed. This conclusion is also consistent with the fact that life on earth
consisted solely of microorganisms for most of its history. Combinatorics of
protein interactions could not, by themselves, lift that complexity ceiling.
Eukaryotes must have found a solution to this problem. Logic and the available
evidence suggest that the rise of multicellular organisms over the past billion
years was a consequence of the transition to a new control architecture based
largely on endogenous digital RNA signals. It would certainly help explain the
phenomenon of the Cambrian explosion about 525 million years ago, when
invertebrate animals of jaw-dropping diversity evolved, seemingly abruptly, from much
simpler life. Indeed, these results suggest a general rule with relevance
beyond biology: organized complexity is a function of regulatory
information--and, in virtually all systems, as observed by Marie E. Csete, now at Emory
University School of Medicine, and John C. Doyle of the California Institute of
Technology, explosions in complexity occur as a result of advanced controls and
embedded networking. The implications of this rule are staggering. We may have
totally misunderstood the nature of the genomic programming and the basis of
variations in traits among individuals and species. The rule implies that the
greater portion of the genomes in complex organisms is not junk at all--rather
it is functional and subject to evolutionary selection. The most recent
surprise is that vertebrate genomes contain thousands of noncoding sequences that
have persisted virtually unaltered for many millions of years. These sequences
are much more highly conserved than those coding for proteins, which was
totally unexpected. The mechanism that has frozen these sequences is unknown, but
their extreme constancy suggests that they are involved in complex networks
essential to our biology. Thus, rather than the genomes of humans and other
complex organisms being viewed as oases of protein-coding sequences in a desert of
junk, they might better be seen as islands of protein-component information in
a sea of regulatory information, most of which is conveyed by RNA. The
existence of an extensive RNA-based regulatory system also has ramifications for
pharmacology, drug development and genetic screening. Traditional genetic
diseases such as cystic fibrosis and thalassemia are caused by catastrophic
component damage: one of the individual's proteins simply doesn't work. Yet many, if
not most, of the genetic variations determining susceptibility to most diseases
and underpinning our individual idiosyncrasies probably lie in the noncoding
regulatory architecture of our genome that controls growth and development.
(Noncoding RNAs have already been linked with several conditions, including B
cell lymphoma, lung cancer, prostate cancer, autism and schizophrenia.) Such
defects will not be easy to identify by molecular genetic epidemiology, nor will
they necessarily be easy to correct. But understanding this regulatory system
may ultimately be critical to understanding our physical and psychological
individuality, as well as trait variation in plants and animals. It may also be
the prelude to sophisticated strategies for medical intervention to optimize
health and for truly advanced genetic engineering in other species. Aside from
introns, the other great source of presumed genomic junk--accounting for
about 40 percent of the human genome--comprises transposons and other repetitive
elements. These sequences are widely regarded as molecular parasites that, like
introns, colonized our genomes in waves at different times in evolutionary
history. Like all immigrants, they may have been unwelcome at first, but once est
ablished in the community they and their descendants progressively became
part of its dynamic--changing, contributing and evolving with it. Good, albeit
patchy, evidence suggests that transposons contribute to the evolution and
genomic regulation of higher organisms and may play a key role in epigenetic
inheritance (the modification of genetic traits). Moreover, this past July Erev Y.
Levanon of Compugen and colleagues elsewhere announced an exciting discovery
involving a process called A-to-I (adenosine-to-inosine) editing, in which an
RNA sequence changes at a very specific site. They demonstrated that A-to-I
editing of RNA transcripts is two orders of magnitude more widespread in humans
than was previously thought and overwhelmingly occurs in repeat sequences
called Alu elements that reside in noncoding RNA sequences. A-to-I editing is
particularly active in the brain, and aberrant editing has been associated with a
range of abnormal behaviors, including epilepsy and depression. Although RNA
editing occurs to some extent in all animals, Alu elements are unique to
primates. An intriguing possibility is that the colonization of the primate lineage
by Alu elements made it possible for a new level of complexity to arise in RNA
processing and allowed the programming for neural circuitry to become more
dynamic and flexible. That versatility may have in turn laid the foundation for
the emergence of memory and higher-order cognition in the human species.
Finally, understanding the operation of the expanded and highly sophisticated
regulatory architecture in the genomes of complex organisms may shed light on the
challenges of designing systems capable of self-reproduction and
self-programming-that is, true artificial life and artificial intelligence. What was
dismissed as junk because it was not understood may well turn out to hold the
secrets to human complexity and a guide to the programming of complex systems in
general. MORE TO EXPLORE Darwin's Dangerous Idea. Daniel C. Dennett. Simon and
Schuster, 1995. Challenging the Dogma: The Hidden Layer of Non-Protein-Coding
RNAs In Complex Organisms. John S. Mattick in BioEssays, Vol. 25, No. 10,
pages 930-939; October 2003. The Unseen Genome: Gems among the Junk. W. Wayt
Gibbs in Scientific American, Vol. 289, No. 5, pages 46-53; November 2003.
Noncoding RNAs: Molecular Biology and Molecular Medicine. Edited by J. Barciszewski
and V. A. Erdmann. Landes Bioscience/Eurekah.com, Georgetown, Tex., 2003.
More information and lists of publications will be found at the author's Web site
[under construction] at http://imb.uq.edu.au/groups/mattick GRAPH:
NONPROTEIN-CODING SEQUENCES make up only a small fraction of the DNA of prokaryotes.
Among eukaryotes, as their complexity increases, generally so, too, does the
proportion of their DNA that does not code for protein. The noncoding sequences
have been considered junk, but perhaps it actually helps to explain organisms'
complexity. DIAGRAM: PROPOSED PRECURSOR molecule for microRNAs is a primary
RNA transcript that may produce multiple small RNAs. The structure of the
precursor might guide the excision of these small RNA signals. DIAGRAM:
UNICELLULAR LIFE, primarily prokaryotes, ruled the earth for billions of years. When
multicellular life appeared, however, its complexity rose with dizzying speed.
The evolution of an additional genetic regulatory system might explain both the
jump to multicellularity and the rapid diversification into complexity. PHOTO
(COLOR): BACTERIA AND HUMANS differ greatly in their structural and
developmental complexity, but biologists have long assumed that all organisms used the
same genetic mechanisms. Yet new work hints that complexity arises from an
additional program hidden in "junk" DNA. ~~~~~~~~ By John S. Mattick JOHN S.
MATTICK, born and raised in Sydney, today is a professor of molecular biology
at the University of Queensland and director of the Institute for Molecular
Bioscience. Formerly he was also foundation director of the Australian Genome
Research Facility. His accomplished career includes the development of
Australia's first genetically engineered vaccine. In 2001 Mattick was appointed an
Officer in the Order of Australia, and in 2003 he was awarded the Australian
government's Centenary Medal. Married with three sons, he enjoys walking and body
surfing as time permits. AN EVOLVING VIEW OF GENE ACTIVITY GENE ACTIVITY IN
PROKARYOTES Prokaryotes (bacteria and other simple cells] have DNA that
consists almost entirely of protein-coding genes. When those genes are active, they
give rise to RNA transcripts that are immediately translated into proteins,
which in turn regulate genetic activity and provide other functions. TRADITIONAL
VIEW OF GENE ACTIVITY IN EUKARYOTES In the DNA of eukaryotes (complex
organisms), individual genes comprise "exon" sequences that code for segments of
protein separated by noncoding "intron" sequences. When a gene is active, it is
entirely transcribed as RNA, but then the intronic RNA is spliced out and the
exonic RNA is assembled as messenger RNA. The cell translates the messenger RNA
into protein while breaking down and recycling the intronic RNA, which serves
no purpose. NEW VIEW OF GENE ACTIVITY IN EUKARYOTES Some of the intronic RNA
and even some of the assembled exonic RNA may play a direct regulatory role by
interacting with the DNA, other RNA molecules or proteins. By modifying
protein production at various levels, these noncoding RNAs may superimpose
additional genetic instructions on a cell. DIAGRAM DIAGRAM DIAGRAM Copyright of
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----------
Howard Bloom
Author of The Lucifer Principle: A Scientific Expedition Into the Forces of
History and Global Brain: The Evolution of Mass Mind From The Big Bang to the
21st Century
Visiting Scholar-Graduate Psychology Department, New York University; Core
Faculty Member, The Graduate Institute
www.howardbloom.net
www.bigbangtango.net
Founder: International Paleopsychology Project; founding board member: Epic
of Evolution Society; founding board member, The Darwin Project; founder: The
Big Bang Tango Media Lab; member: New York Academy of Sciences, American
Association for the Advancement of Science, American Psychological Society, Academy
of Political Science, Human Behavior and Evolution Society, International
Society for Human Ethology; advisory board member: Youthactivism.org; executive
editor -- New Paradigm book series.
For information on The International Paleopsychology Project, see:
www.paleopsych.org
for two chapters from
The Lucifer Principle: A Scientific Expedition Into the Forces of History,
see www.howardbloom.net/lucifer
For information on Global Brain: The Evolution of Mass Mind from the Big Bang
to the 21st Century, see www.howardbloom.net
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