Epigenetics of Reproduction in Animals - Building the Most Complex Structure on Earth - page 72

In a number of cases, the neurally induced DNA methylation is transmitted to
subsequent generations and leads to the inheritance of acquired characters in meta-
zoans. The illustrating example is the methylation of the bdnf gene. Licking and
grooming (LG) is a characteristically inherited behavior in rats. In this respect, there
are high-LG and low-LG rat mothers. Maternal high-LG behavior during the first
postnatal week is processed in the brain cortex of rat puppies where it activates a
signal cascade that leads to DNA demethylation and secretion of the neurotransmit-
ter serotonin in their hipocampal neurons. The binding of serotonin by its receptor
triggers a signal transduction pathway that leads to the activation of the gene NGFIA
(nerve growth factor-inducible A) or egfr , inducing DNA demethylation and opening
of the chromatin, thus enabling expression of the glucocorticoid receptor ( GR ) gene
( Figure 2.5 ). As mothers, these puppies display the same high LG for their puppies.
However, when these puppies are reared by low-LG mothers they show their off-
spring the same low-LG behavior of their adopted mother rather than the high-LG
behavior of their biological mother. The reason for the transmission of the acquired
character (low-LG behavior) is that the processing of the insufficient maternal LG in
the brain cortex leads to DNA methylation and insufficient production of GR ( Szyf
et al., 2007 ).

Parental care
Licking and grooming

GCs
Feedback
to the brain

Andrenal
gland

Processing of the
maternal tactile stimuli
in the cerebral cortex

ACTH Secretion of serotonin

in hipocampal neurons

Serotonin

Serotonin
receptor

Blinding of serotonin
receptor

Pituitary

Secretion of NGFI-A

NGFI-A

CRH

DNA demethylation
and chromatin opening

GR gene NGFI-A

gene

Nucleus

GR

GR gene

Hypothalamus

GR synthesis

Hipocampal neuron

Figure 2.5 The mechanism of transmission of the high-LG behavior in female rats. GR,
glucocorticoid receptor; CRH, corticotrophin-releasing hormone; ACTH, adrenocorticotropic
hormone; GC, glucocorticoid.