Morphogens: Precise Outputs from a Variable Gradient

Morphogens: Precise Outputs from a Variable Gradient

The morphogen gradient as a source of embryonic patterning is one of the best accepted concepts in developmental biology. Morphogens can be transcription factors or extracellular signals, but in both cases, they are thought to provide concentration thresholds that position different cell fates within the developing embryo. Several recent papers examine the patterning activities of Drosophila Bi...

Morphogens

Hands have five fingers, with each finger different and arranged in a particular order. Obvious perhaps, but the way that this arrangement is achieved during development has intrigued developmental biologists for decades. How do the cells of the hand know whether to form a thumb, index or little finger? More generally, how do cells know where they are within a tissue so that they form the appro...

Morphogens, Compartments, and Pattern: Lessons from Drosophila?

Peter A. Lawrence* and Gary Struhl† Epigenesis, at least in Drosophila, depends on three steps which interlock and overlap; we simplify and refer *Medical Research Council Laboratory of Molecular Biology to these as the “central dogma.” First, positional information in the form of morphogen gradients allocates Hills Road Cambridge CB2 2QH cells into nonoverlapping sets, each set founding a comp...

Nodal morphogens.

Nodal signals belong to the TGF-beta superfamily and are essential for the induction of mesoderm and endoderm and the determination of the left-right axis. Nodal signals can act as morphogens-they have concentration-dependent effects and can act at a distance from their source of production. Nodal and its feedback inhibitor Lefty form an activator/inhibitor pair that behaves similarly to postul...

Variable Metric Conjugate Gradient Methods