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Figure 10.1 Development from a single fertilized oocyte (zygote) to adult. Early-
stage blastocyst is shown with inner cell mass. At this stage, key transcriptional
factors are at work in either maintaining pluripotency or directing differentiation
into tissues of mesoderm, ectoderm, and endoderm lineages. A later-stage
embryo shows the emergence of body shape with head, body, and limb buds
and somites for the musculoskeletal system. Different transcriptional pathways
are recruited, and the known dominant developmental players are shown here,
including Wnt , TGF- b /BMP , Notch , and noncoding RNAs. At each stage, in the
background, is shown the interaction of gene networks.
reflects an adherence to programmed and coordinated activation and
suppression of regulatory gene networks (figure 10.1). This involves
the primordial reprogramming of highly differentiated oocyte and
sperm genomes into the trophectoderm and primitive endoderm that
form the extraembryonic tissues, such as the placenta, required for sup-
porting the development of the embryo proper and the pluripotent
cells of the epiblast/inner cell mass (ICM). It is the ICM that develops
into the newborn. The information needed to understand developmen-
tal biology therefore requires multidimensional considerations. The
most elementary level of information required is that about the genes
and their products. There is still much knowledge to gather and organize
for all the genetic products involved, which include coding and noncod-
ing transcripts. There is the critical dimension of precise chronological
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