Epigenetic Control of Animal Development - Building the Most Complex Structure on Earth - page 148

Eventually NCCs settle in the destination site, and like zealous missionaries
“leading by example,” start instructing the local uncommitted population of cells on
what type of cell they need to become. Adequate evidence suggests that this conver-
sion is induced by NCC newcomers. Experiments of transplantation of duck neu-
ral crest for beaks in quails and vice versa provide elegant proof: in both cases, the
chimera inherits the beak of the donor (i.e., duck beaks in quails and quail beaks in
ducks). According to a study by Schneider and Helms (2003) :
Neural crest cells provide patterning information for beak morphology. Not only do
NCCs direct their own morphogenesis, they also pattern nonneural crest beak tis-
sues in a manner characteristic of donor species.
Epigenetic Control of Postphylotypic Development
in Animals
Parental Epigenetic Information Is Exhausted at the Phylotypic
Stage—Where Does the Information for Further Development
Come from?
Although certain maternal factors are active during the formation of the nervous
system and even during the phylotypic stage in relation to the formation of somites
( Kotani and Kawakami, 2008 ), as we have seen, the parental information that drives
the early embryonic development until the formation of the Bauplan at the phylo-
typic stage is practically exhausted.
The weaning of the embryo from the source of the parental information on which
the early development and the Bauplan relied on is a turning point from an informa-
tional view. Exhaustion of the parental epigenetic information, far from an informa-
tional catastrophe, comes as an informational change of the guard: the CNS, which
is already operational, takes over the postphylotypic development up to adulthood,
including the formation of gametes provided with the same epigenetic information
that drove the development of the embryo to the phylotypic stage. The CNS, thus,
repays the epigenetic information that the parent or parents invested for its devel-
opment not to the “lender,” but to the next generation in a fair-relay informational
scheme.
To reiterate, the epigenetic information spent to erect the Bauplan was provided to
the embryo via maternal gametic and paternal cytoplasmic factors arranged in spe-
cific patterns in the gametes and the zygote. That information consists of many thou-
sands of mRNAs, proteins, hormones, neurotransmitters, and other elements, which,
as we have shown, determines the development of the zygote up to the formation of
the Bauplan at the phylotypic stage.
The parents neither copy themselves nor provide the full design of the adult
organism. Instead, at the phylotypic stage, they provide the embryo with a young
“designer” that, in the process of development, figures out the structure of the next
stage from the structure of the actual embryonic stage and produces information to