Morphogen protein gradients play an important role in the spatial regulation of patterning during embryonic development. The most commonly accepted mechanism for gradient formation is diffusion from a source combined with degradation. Recently, there has been growing interest in an alternative mechanism, which is based on the direct delivery of morphogens along thin, actin-rich cellular extensi...

Translating a graded morphogen distribution into tight response borders is central to all developmental processes. Yet, the molecular mechanisms generating such behavior are poorly understood. During patterning of the Drosophila embryonic ventral ectoderm, a graded mitogen-activated protein kinase (MAPK) activation is converted into an all-or-none degradation switch of the Yan transcriptional r...

Protein morphogens are instructive signals that regulate growth and patterning of tissues and organs. They form long-range, dynamic gradients by moving from regions of high concentration (producing cells) to regions of low concentration (the adjacent, nonproducing developmental field). Since morphogen activity must be limited to the adjacent target field, we want to understand both how signalin...

The ability to maintain a proportionate body plan in individuals of different sizes is essential for proper development. Despite wide interest, little is known about the mechanisms underlying scaling with size. I will discuss our efforts to reveal the molecular basis for scaling in different systems. A general ‘‘Expansion– Repression’’ feedback topology will be presented, which ensures scaling ...

Retinoic acid (RA) regulates many cellular behaviors during embryonic development and adult homeostasis. Like other morphogens, RA forms gradients through the use of localized sources and sinks, feedback, and interactions with other signals; this has been particularly well studied in the context of hindbrain segmentation in vertebrate embryos. Yet, as a small lipophilic molecule derived from a ...

In Drosophila embryos, a concentration gradient of nuclear Dorsal protein controls pattern formation along the dorsal-ventral axis. Recent quantitative studies agree on the temporal dynamics of the gradient, but disagree on its spatial limits.

BACKGROUND How morphogen gradients form has long been a subject of controversy. The strongest support for the view that morphogens do not simply spread by free diffusion has come from a variety of studies of the Decapentaplegic (Dpp) gradient of the Drosophila larval wing disc. RESULTS In the present study, we initially show how the failure, in such studies, to consider the coupling of transp...

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Bone morphogenetic proteins (BMPs) regulate dorsal/ventral (D/V) patterning across the animal kingdom; however, the biochemical properties of certain pathway components can vary according to species-specific developmental requirements. For example, Tolloid (Tld)-like metalloproteases cleave vertebrate BMP-binding proteins called Chordins constitutively, while the Drosophila Chordin ortholog, Sh...

Morphogen gradients are typically analyzed from static images of fixed embryonic tissues. Two papers in this issue of Cell now report live imaging of the Bicoid gradient in developing fruit fly embryos (Gregor et al., 2007a, 2007b). Their findings indicate that the gradient is highly reproducible from embryo to embryo and reveal that the nuclear dynamics of Bicoid are critical for maintaining p...