Development is a study of how a
biological complexity arises from simple entities. Such as development of an
embryo from a single zygote, or development of a whole organ from a single
cell, or development of consciousness from perceived non-living chemical
substances. Whereas the scientific community struggles to answer the question
“why the complexity comes into being”, the scientists have been successful in
answering the question “how the complexity comes into being” by describing the
molecular mechanisms taking place in living cells.
To for a functioning organ the
cells of any tissue within an organ undergo the basic principles of
development: proliferation, migration, differentiation. For any cell to
maintain its homeostasis and perform the assigned function within its tissue,
it has to acquire a specific cellular identity, which is a set of properties
determined by biological processes taking place in it.
fate or identity can be defined as a set of genetic, morphological, and
physiological characteristics that cells possess at any given time during
development. Differentiation is a change in cell morphology and physiology
during development. Such change is mediated by signaling and transcriptional
changes, and reflected on transcriptomic and proteomic levels. For any organ to
fully form, cells must obtain identity, that would enable them to successfully
divide, migrate, and function at designated locations and times.
Normal functioning of a healthy
organ is a developmental process.
diseased cells the normal biological processes and hence normal functioning is
not taking place. Therefore, to distinguish healthy and diseased cells, in
order to target the disease, one has to
understand the biological processes that underlie cellular identities.
Waddington compared cell
specification towards terminal differentiation with a ball travelling downwards
a long sequence of branching valleys; once a cell differentiates it is
difficult for it to cross the mountain into neighbouring valleys or roll back to
unspecified state6 (Figure 1). Thus, the permanent and semi-permanent changes in
genome activity that underlie cellular differentiation can remain stable for
long periods even when the original stimulus that induced it is not there.