Living and Adapting to Its Own Habitat - Building the Most Complex Structure on Earth - page 198

proteins is mainly induced by hormones of the target endocrine glands and pituitary
as well as neurohormones. This reliably leads to the idea that the ultimate source of
information for expression of nonhousekeeping genes in vertebrates may be the CNS
( Cabej, 2005, 2008 ).
Signals from the CNS are at the origin of processes of development, growth,
and metamorphosis in invertebrates and the neural net in lower vertebrates, such as
cnidarians ( Cabej, 2008, pp. 139-201, 2010, 2012, pp. 149-204 ).
It is well known that differences in expression of nonhousekeeping genes are
responsible for the differentiation of all types of cells starting from a single cell,
zygote, or egg, during individual development. Bearing in mind that the ultimate
source of information for expression of these genes is the CNS (cytoplasmic factors
during the early development up to the phylotypic stage), a hierarchical scheme of
the control of gene expression with the CNS as the controller is easy to envisage.
The advent of the neural regulation of gene expression during the Cambrian explo-
sion was crucial for the evolution of metazoans.
Now, in order to corroborate the above conclusion on the neural origin of infor-
mation for gene expression, we will approach the problem in the reverse direction.
Metazoans respond to environmental stimuli by changing their morphology, physiol-
ogy, behavior, or life history. These adaptive changes involve changes in the normal
patterns of gene expression in relevant tissues and organs. Now we will try to follow
the pathway from the environmental stimuli to gene expression.
The next section shows how the organism sends instructions to genes in a lan-
guage that genes could understand.
Making Environmental Signals Intelligible to Genes
In everyday parlance, environmental stimuli is said to induce or even regulate the
expression of specific genes. This notion is so engraved in the biological concep-
tual system that it comes as a revelation when, upon closer scrutiny, it turns out that
no external stimuli that could directly induce the expression of any gene are known.
No biotic or abiotic agent per se (the viruses' case is irrelevant) is capable of induc-
ing expression of any gene. Yet a clear correlation and causal relationship between
particular environmental agents and expression of particular genes is empirically
demonstrated to exist in more than an adequate number of cases. How is it possi-
ble for environmental agents to “exert” this long-range action on gene expression,
while unable to induce expression of genes in direct contact with them? What is that
which translates the language of external agents into instructions that are intelligible
to genes?
A closer examination of this biological “ alibi ” will reveal to us where the envi-
ronmental agents acquire “meaning” and how this meaning is translated into a lan-
guage that genes could understand. This will shed light into the black box of how
genetically incomprehensible environmental messages are translated into intelligible
instructions for gene expression.