doi: 10.1242/10.1242/dev.00425
Mechanisms of pattern formation in development and evolution
Isaac Salazar-Ciudad1,*,
Jukka Jernvall1 and
Stuart A. Newman2
1 Developmental Biology Program, Institute of Biotechnology, PO Box 56,
FIN-00014, University of Helsinki, Helsinki, Finland
2 Department of Cell Biology and Anatomy, New York Medical College, Valhalla, NY
10595, USA
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Fig. 1. Schematic examples of the basic developmental mechanisms. Division of
an heterogeneous egg: different parts of the egg bind different molecules
(indicated by different shading) resulting in different blastomere cells.
Asymmetric mitosis: molecules are differentially transported into
different parts of a cell resulting in different daughter cells. Internal
temporal dynamics coupled to mitosis: cells that have oscillating levels
of molecules before their division can produce spatial patterns.
Hierarchic induction: inducing cell (gray) affects neighboring cells
but the induced cells (white) do not affect the production of the inducing
signal. Emergent induction: inducing cell affects neighboring cells,
which in turn signal back affecting the production of the inducing signal.
Directed mitosis: consistently oriented mitotic spindles may direct
tissue growth. Differential growth: cells dividing at a higher rate
(gray) can alter tissue shape. Apoptosis: transformation of an
established pattern into another can result from apoptosis affecting specific
cells (gray). Migration: cells can migrate to a new location.
Adhesion: a change in pattern can result if a set of cells have
differential adhesion properties (strong adhesion among gray cells).
Contraction: differential contraction of cells can cause buckling of
a tissue. Matrix swelling, deposition, and loss: matrix swelling can
cause budding.
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Fig. 2. Combining signaling and morphogenesis. Inductive (signaling) and
morphogenetic mechanism can be combined to generate morphostatic
mechanisms where induction (in red) temporally precedes growth, producing the
final forms. Morphodynamic mechanisms, in contrast, integrate
inductive and morphogenetic mechanisms and can often be difficult to separate
as induction and final development of the shape are concurrent.
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Fig. 3. Morphodynamic interactions can result in complex patterns. (A) Forms of
interacting territories can affect induced patterns. In this example,
curvature of the target tissue affects whether one small, two small or one
large territory is induced (black). (B) Distance of interacting territories
can also affect the number and size of induced territories. Note that beyond a
certain distance between territories, no pattern changes will occur. (C)
Actual spatial patterns of induced territories can be complex with large
changes produced by small changes in interacting territories. The actual
patterns may also be difficult to infer from histological sections (e.g.,
vertical line in C represents location of corresponding sections in B).
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Fig. 4. A schematic illustration of how morphostatic and morphodynamic mechanisms
have different variational properties. A simple change in tissue growth does
not affect induction (red) and the resulting pattern in a morphostatic system
because only growth of initially induced territories is affected, resulting in
slightly blunter or sharper features. In morphodynamic mechanisms small
changes in growth can alter induction of new territories
(Fig. 3), resulting not only in
blunter or sharper features, but completely altered patterns. Morphostatic
mechanisms would require large changes in induction of territories in order to
produce comparable change, particularly in the case of positional information
systems where each new territory would require a unique signal or signal
concentration. In general, morphodynamic mechanisms can be hypothesized to
produce more disparate morphological outcomes than morphostatic
mechanisms.
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© The Company of Biologists Ltd 2003
