Editing Morphogenesis (section)

==Genetic and molecular basis==
[[File:Gap gene expression.svg|thumb|upright=0.8|[[Evolutionary developmental biology|Morphogenesis is controlled]] by a [[evo-devo gene toolkit|"toolkit" of genes]] which switch development on and off at precise times and places. Here, [[gap gene]]s in the fruit fly are switched on by genes such as ''[[bicoid]]'', setting up stripes which create the body's segmental form.]]
{{further|evolutionary developmental biology|transcription factor|gene regulatory network}}

Several types of molecules are important in morphogenesis. [[Morphogen]]s are soluble molecules that can diffuse and carry signals that control cell differentiation via concentration gradients. Morphogens typically act through binding to specific protein [[receptor (biochemistry)|receptor]]s. An important class of molecules involved in morphogenesis are [[transcription factor]] proteins that determine the fate of cells by interacting with [[DNA]]. These can be coded for by master regulatory [[gene]]s, and either activate or deactivate the [[Transcription (genetics)|transcription]] of other genes; in turn, these secondary gene products can regulate the expression of still other genes in a regulatory cascade of [[gene regulatory network]]s. At the end of this cascade are classes of molecules that control cellular behaviors such as [[cell migration]], or, more generally, their properties, such as [[cell adhesion]] or cell contractility. For example, during [[gastrulation]], clumps of [[stem cell]]s switch off their cell-to-cell adhesion, become migratory, and take up new positions within an embryo where they again activate specific cell adhesion proteins and form new tissues and organs. Developmental signaling pathways implicated in morphogenesis include [[Wnt signaling pathway|Wnt]], [[Hedgehog signaling pathway|Hedgehog]], and [[ephrin]]s.<ref>{{cite journal |last=Kouros-Mehr |first=H. |author2=Werb, Z.|title=Candidate regulators of mammary branching morphogenesis identified by genome-wide transcript analysis |journal=Dev. Dyn. |year=2006 |volume=235 |issue=12 |pages=3404–12 |pmid=17039550 |doi=10.1002/dvdy.20978 |pmc=2730892 }}</ref>