Agriculture Reference
In-Depth Information
state (Meins and Lutz 1979; Meins 1996). These experiments tie together
five important concepts of epigenetics:
1. Cells gain and lose the trait at very high frequency, thus appearing
not to be due to spontaneous changes in DNA sequence (mutations)
(Meins and Binns 1977, 1982).
2. The phenotype change occurs in response to the environment, for
example, prolonged exposure to the absence of the hormone (Meins
et al. 1980; Meins and Seldran 1994).
3. Habituation is transgenerational, that is, it is inherited meiotically
in a non-Mendelian fashion because the altered trait is not 100%
reset through meiosis or it is sometimes not preserved in the germ
line during production of gametes and zygote development (Meins
and Wenzler 1986; Meins 1996).
4. It is dependent on the developmental state of the cell since only
cortex cells display the failure to reset or carry through the normal
phenotype (nonhabituated) through meiosis, thus revealing the
existence of an inheritable epigenetic memory that is not the
same for all somatic cell types (Meins and Lutz 1979).
5. Finally, identi
cation of a Mendelian locus that controls the habit-
uation epigenetic phenotype provided evidence that the genetic
and epigenetic systems are connected by a control loop (Meins et al.
1983).
These observations of Meins and coworkers on the concept of an
epigenetic memory were supported by even earlier work using animal
nuclear transplantation. Nuclei taken from somatic cells at different
points in ontogeny appeared to retain the
of the somatic stage
from which the nuclei were taken (Gurdon 1963). Remarkably, in more
recent experiments, using nuclei with gene expression markers that are
speci
“
memory
”
c for particular somatic cell types, Ng and Gurdon (2005) found
that this epigenetic memory detected by ontogenetic speci
c marker
gene expression can persist in error through development because the
markers are misexpressed in the wrong cell types of embryos that
develop from the transplanted nuclei.
These early reports did not spark a dramatic renewed interest in non-
Mendelian inheritance and a renaissance in understanding epigenetics
as they should have. They partly may have been neglected because they
did bring together some strange bedfellows: the concepts of development
and epigenetics of Waddington and the environment-directed and trans-
generational aspect of phenotypes proposed by Lamarck.
