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Segmentation Clock (segmentation + clock)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Sharp developmental thresholds defined through bistability by antagonistic gradients of retinoic acid and FGF signaling

DEVELOPMENTAL DYNAMICS, Issue 6 2007
Albert Goldbeter
Abstract The establishment of thresholds along morphogen gradients in the embryo is poorly understood. Using mathematical modeling, we show that mutually inhibitory gradients can generate and position sharp morphogen thresholds in the embryonic space. Taking vertebrate segmentation as a paradigm, we demonstrate that the antagonistic gradients of retinoic acid (RA) and Fibroblast Growth Factor (FGF) along the presomitic mesoderm (PSM) may lead to the coexistence of two stable steady states. Here, we propose that this bistability is associated with abrupt switches in the levels of FGF and RA signaling, which permit the synchronized activation of segmentation genes, such as mesp2, in successive cohorts of PSM cells in response to the segmentation clock, thereby defining the future segments. Bistability resulting from mutual inhibition of RA and FGF provides a molecular mechanism for the all-or-none transitions assumed in the "clock and wavefront" somitogenesis model. Given that mutually antagonistic signaling gradients are common in development, such bistable switches could represent an important principle underlying embryonic patterning. Developmental Dynamics 236:1495,1508, 2007. © 2007 Wiley-Liss, Inc. [source]

And the segmentation clock keeps ticking

BIOESSAYS, Issue 5 2007
Moisés Mallo
The vertebrate body is organized in segments, easily visible in the consecutive vertebrae of the skeleton. These are first defined in the embryo by the formation of somites. Somites are generated at regular intervals from the presomitic mesoderm by a combination of oscillating signals, known as the segmentation clock, which establish the pace at which new somites are formed, and signaling gradients that set the location of new intersomitic borders. Using a microarray approach, Dequéant et al.1 have now shown that the segmentation clock is more complex than previously thought and includes oscillating expression of genes from at least three signaling pathways organized in coordinated networks. BioEssays 29:412,415, 2007. © 2007 Wiley Periodicals, Inc. [source]

A Hes1-based oscillator in cultured cells and its potential implications for the segmentation clock

BIOESSAYS, Issue 3 2003
J. Kim Dale
During somitogenesis an oscillatory mechanism termed the "segmentation" clock generates periodic waves of gene expression, which translate into the periodic spatial pattern manifest as somites. The dynamic expression of the clock genes shares the same periodicity as somitogenesis. Notch signaling is believed to play a role in the segmentation clock mechanism. The paper by Hirata et al.(1) identifies a biological clock in cultured cells that is dependent upon the Notch target gene Hes1, and which shows a periodicity similar to that of the segmentation clock. This finding opens the possibility that the same oscillator mechanism might also operate in other tissues or cell types. BioEssays 25:200,203, 2003. © 2003 Wiley Periodicals, Inc. [source]