NC:-
Quoted message said:As we all know, from 10-30,000 genes of the metazoan
genome, several thousands, the so-called HOUSEKEEPING
GENES, are needed for the subsistence and reproduction of
metazoan cells and are expressed some time during the
lifetime of the cell. The rest, i.e. the majority of them
are NONHOUSEKEEPING GENES, which perform extracellular,
organismic functions and are expressed differentially in
different types of cells. Their extracellular function
determines the extracellular origin of signals for their
expression, for no cell could figure out what the
organism might need at any particular point in time (cell-
cell interactions come to mind but they will later be
dealt with).
Quoted message said:JE:- OK
Quoted message said:NC:-
.........................................................
Quoted message said:JE:- OK. Epigenetic control hierarchies exist which may be
much larger within metazoan forms such that they can alter
the phenotype expressed from the same set of genes.
NC (is NC you correct initials?): Thus, you agree that the
expression of nonhousekeeping genes, which are responsible
for cell differentiation and cell-cell interactions, is
under epigenetic (NONGENETIC) control.
JE:- Yes. Note however that epigenetic products are
ultimately coded for by genes. "Everything" can be reduced
to just genes when reductive reasoning (deduction) is
misused. This is something like reducing a work of
Shakespeare to just a word count. When you do this, 99% of
the information is deleted. What you are fighting against is
the reductive view that we are just the sum of our genes.
NC:- In view of the fact that all the stages of metazoan
reproduction (gametogenesis, early development and
organogenesis) depend on cell differentiatiion, it follows
that this epigenetic system, or these "epigenetic control
hierarchies", regulates the individual development in
metazoans.
JE:- It is a classical "chicken and egg" argument. The CNS
regulates genes but genes code for the CNS. So what came
first, the genes or the CNS? The answer is neither. They
evolved _together_ within a _single_ unit of selection.
Epigenetic systems of inheritance have been documented
within nature. The problem is, how do you experimentally
separate out Mendelian gene inheritance from an epigenetic
level of inheritance? Classical analytical genetics will
just "see through" any proposed epigenetic level to only
resolve the most basic level: the gene. Epigeneticists will
have to readjust their deductive microscopes to only resolve
a low power of magnification.
Quoted message said:NC:- What we need to demonstrate is that all the stages of
animal reproduction, starting with the formation of gametes
and individual development are
under
Quoted message said:the CNS control and regulation.
Quoted message said:JE:- I think you are arguing that the CNS is the last
(highest) epigenetic system that exists so that it has the
power of direction of the phenotype. In my diagram this
means the CNS would be E2 where E2 is limited by E1 and E1
is limited by G.
NC:- I would rather say that there is one integrated
control system, with the CNS as its controller that is
limited by genes (G), as well by numerous external and
internal stimuli.
JE:- Ok. I attempt to illustrate this in the following way:-
selective forces
|
V
+-----------------------------+
selective | | selective
forces ---> | genes --->epigenes---->CNS | <--- forces
| |
| |
+-----------------------------+
^
|
selective forces
The box represents a single Darwinian unit of selection (one
fertile form). Selective forces surround it,
i.e. they act on every level within the box strictly
however, at just the one level of selection which the
dotted line of the box represents: one fertile form.
Within each fertile form genes can only limit epigenes and
likewise, epigenes can only limit the CNS which is here,
supposed as the highest (most complex) epigenetic level
within each Darwinian form. Any deduction from the CNS must
end up with just, genes. The reductionist "misses" the other
two levels by "seeing through" them. Inductive theory
building sees in the direction of the arrows within each
independently selected box but analytical deductive theory
can only see against the arrows. Epigenes become the meat in
the sandwich because they control gene expression but at the
same time limit CNS action. In this respect they may be
missed by both reductive and inductive investigation.
Quoted message said:NC:- Adequate experimental evidence already shows that the
CNS (to be more
exact,
Quoted message said:the integrated control system, which besides the CNS
comprises the mechanisms for monitoring the status of the
living system in general as well as the pathways for
transmission to the cells all over the animal body of the
epigenetic information generated in neural circuits)
controls and regulates:
1. The formation of the egg and sperm cells
2. The placement of maternal cytoplasmic factors in the
egg cell.
3. The early embryonic development (which is regulated not
by zygotic
genes,
Quoted message said:but by maternal cytoplasmic factors) up to the phylotypic
stage, when a functioning CNS first arises.
4.The postphylotypic development, including the post-natal
development (the
Quoted message said:JE:- Could you provide one example of each of the above?
NC:- "One example of each of the above" is a reasonable
challenge, even though examples abound.
1. The formation of the egg and sperm cells
a. In the female fire ant, Solenopsis invicta, the
electrical activation of the dopamine system resulting
from the PROCESSING of an external stimulus (queen
pheromone) in the brain controls oogenesis and
oviposition (Boulay et al 2000).
JE:- It would be interesting to find out if the activation
of this dopamine system could be preactivated by epigenetic
inheritance of queen pheromone.
NC:-
b. For more than two decades it is generally acknowledged
that spermatogenesis "is ultimately controlled by neurons
in the CNS" (Sharp and Gow 1983) and that the CNS exerts
that control via the GnRH pulse generator and the hypothalamic-pituitary-
testicular axis (Vander).
Quoted message said:2. The placement of maternal cytoplasmic factors in the
egg cell.
In the canary, Serinus canaria, the seasonal changes of
photoperiod are processed in the brain and via hypothalamic-pituitary-
ovarian axis determine the concentration of maternal
testosterone in the egg (Schwabl, 1993).
Quoted message said:3. The early embryonic development (which is regulated not
by zygotic
genes,
Quoted message said:but by maternal cytoplasmic factors) up to the phylotypic
stage, when a functioning CNS first arises.
Since -the parental CNS regulates the placement of maternal
cytoplasmic factors in the egg cell, and -maternal
cytoplasmic factors regulate the early development (Wolpert
et al 1998; Hall 1998; Gilbert 2000, etc etc.) -THE PARENTAL
CNS(s) REGULATE THE EARLY DEVELOPMENT (since A regulates B
and B regulates C)
Quoted message said:4.The postphylotypic development, including the post-natal
development (the
During embryogenesis the sensory neurons and Schwann cells
secrete VEGF, which determines the cell differentiation and
patterning of arteries in their vicinity what explains the
old anatomic observation on the general association of
arteries and peripheral nerves (Mukoyama et al. 2002). One
more example. For a long time it has been believed that the
expression of the Sry gene on the chromosome Y induces the
development of testes and hormones secreted by testes
determine the specific organization of the male
differentiation of the brain starts before the expression of
the Sry gene on the chromosome Y, before the testes are
formed and testosterone is secreted (Dewing et al 2003).
Recently (2003) in the Proc.Natl. Acad. Sci. USA, a
naturally occurring zebra finch was reported to be male
(with testis) on the right side and female (with an ovary)
on the left, although genes and the circulating hormones are
the same in both sides. Only brain circuits on the right
side are of different male patterning. I believe the
epigenetic system of heredity in metazoans is an obvious
reality. The examples presented here and numerous others
clearly show that the expression of nonhousekeeping genes
and the main stages of individual development are under
control of an epigenetic control predicted by J. Maynard
Smith. Thank you for giving me the opportunity to argue and
substantiate the existence of this system. Further input and
critical remarks from you, r. norman, and others in the sbe
are wellcomed and appreciated.
JE:- Thank you for your scholarly discourse. However for the
gene centrics that dominate this site most will just falsely
conclude that in the end, it is all just reducible to genes.
I agree that "the epigenetic system of heredity in metazoans
is an obvious reality" but proving the obvious is no easy
task but remains, essential. Nobody seems to be interested
in attempting to measure epigenetic inheritance because the
genetic component of it (which has to exist) must be
entirely removed within a properly controlled experiment.
Indeed, prejudice against investigating epigenetic systems
within evolutionary theory because of ancient echoes of
Lamarck's "acquired characters", remains so enormous that it
seems to me that researchers are going out of their way to
avoid observing any epigenetic heritability in the dire fear
of being labelled a Lamarckian heretic and having their
research grants stopped.
Genes remain today's new toys and not epigenes. I think a
good strategy would be to create a hot list of documented
heritable epigenetic events and post it to sbe for comment.
Respectfully,
John Edser Independent Researcher
PO Box 266 Church Pt NSW 2105 Australia
[email hidden]