Epigenetics of Reproduction in Animals - Building the Most Complex Structure on Earth - page 84

Reception

Binding of growth
factor to receptor

Cytosol

Active
relay protein

Inactive
relay protein

P

Inactive
protein
kinase 1

Active
protein
kinase 1

P

Tr ansduction Active

protein
kinase 2

Inactive
protein
kinase 2

P

Active
protein
kinase 3

Inactive
protein
kinase 3

Nucleus

Inactive
transcription
factor

Active
transcription
factor

Response

P

DNA

Gene

mRNA

Figure 2.13 A generalized model of a signal transduction pathway.
Source : From http://biotecnologieindustriali.campusnet.unito.it/do/corsi.pl/Show?_id=2a54 .

the target endocrine glands (thyroid, thymus, pancreas, adrenals, ovaries, and testi-
cles) are induced by “stimulating” hormones released by the pituitary, which in turn
are induced by respective neurohormones secreted by the brain. Many growth factors
such as epidermal growth factor, transforming growth factor (TGF), and fibroblast
growth factor are induced by various hormones of the target endocrine glands, but
all of these hormones are induced by the respective pituitary stimulating hormones,
which, in turn, are induced by corresponding neurohormones of the hypothalamus
(see Cabej, 2005, 2012, pp. 23-24 for relevant sources). Wnt-4, a member of the
family of secreted glycoproteins of the Wnt family, is necessary for the ductal side
branching in the mammary gland ( Brisken et al., 2000; Robinson et al., 2000 ), but
Wnt-4 secretion is stimulated by the pituitary prolactin, which in turn is inhibited/
induced neurally by the opioid system ( Aurich et al., 2001; Soaje and Deis, 1997;
Soaje et al., 2002 ). Proteoglycans, a major component of the ECM, are regulated by
local innervation ( Brandan et al., 1992 ).