Biology Reference
In-Depth Information
FIGURE 1.1
A typical develop-
mental 'blob and arrow' diagram, in
which signalling events are depicted in
detail but morphogenesis is treated as
a black box. This particular diagram is
adapted from one of my own summar-
ies of processes that control renal
development.
10
BMPs
TGFb
Activin
GDNF
HGF
TGFa
FGFs
BMPR
Met
TGFR
ActR
Ret
EGFR
FGFR
Erk MAPK
Smad1
Smad2/3
Branching
morphogenesis
developmental biology temporarily, but they have allowed researchers to create tools that are
powerful enough to be applied fruitfully to morphogenesis itself. Very recently, mainly in the
21st century, the application of these tools has begun to transform our understanding of how
cells can translate a 'command' to make a shape into that shape itself. The long-sought
molecular mechanisms of morphogenesis are now being glimpsed for the first time.
The purpose of this topic is to bring together in one place some of the most significant
advances that have been made in identifying mechanisms of morphogenesis from a variety
of species, systems and scales. The field is at too young a stage for the topic to be able to
present a complete, rounded story. Rather, it provides examples of the mechanisms that
have been found, or are strongly suspected, to drive the types of morphogenetic event
most common in animal and plant development. The order of chapters in the topic does
not follow the order of events in the development of any particular organism, but is instead
organized approximately by scale. It begins with the self-assembly of supramolecular
complexes, which is the foundation on which everything else rests. It then considers the
morphogenesis of individual cells and works mainly upwards in size towards the scale of
tissues. This order has been chosen carefully, because the morphogenetic mechanisms
described in later chapters tend to invoke, and 'take for granted' the fine-scale mechanisms
described in earlier chapters. Cross-references between chapters have been provided, wher-
ever possible, for readers who are 'dipping' rather than reading cover to cover.
As well as concentrating on the molecular biology of morphogenetic mechanisms, this
topic lays some stress on the more abstract principles that seem to be emerging from them.
There are two reasons for this. The first is that it is easier for an author to present, and for
a reader to understand, detailed molecular information when there is a framework on which
it can be organized. The second is a stubborn belief on the part of the author that there must
be more to understanding biology than a lot of diagrams with blobs and arrows. The issue of
'understanding' morphogenetic mechanisms is discussed further in Chapter 28. The prin-
ciples that run most pervasively through this topic are introduced in Chapter 2; readers
intending only to dip into the sections of this topic that are most relevant to them are encour-
aged to look at Chapter 2 first, because it will define terms used in later chapters.
