In vertebrate somitogenesis, the expressions of
"segmentation clock" genes show oscillation, synchronized over nearby
cells through cell-cell interaction in the tissue, presomitic mesoderm
(PSM). The locations of high gene expression appear with regular
intervals and move like a wave from posterior to anterior with the
speed slowing down.
In this seminar I will first talk about the effect of cell
movement observed in the posterior PSM on synchronization of the
segmentation clock. We show by numerical modeling that synchronized
oscillation can be sustained under random cell movement. We find that
the synchronization of cells is recovered much faster after initial
phase disturbances and it is for a wider range of reaction parameters
than the case without cell movement. When the posterior PSM is
rectangular, faster synchronization is achieved if cells exchange
their locations more with neighbors located along the longer side of
the domain.
Second I will talk about traveling wave formation of the
segmentation clock when there is an anterior-posterior gradient of one
of the reaction rates in the gene-protein kinetics. We show that the
observed spatio-temporal pattern can be explained if mRNA degradation,
protein translation, protein transport to nucleus occurs faster, or
mRNA transcription, Delta protein synthesis occurs slower in posterior
than in anterior regions. All of these gradients are those that
produce longer periodicity of oscillation of clock gene expression in
the anterior than in the posterior. Based on this result, we derive a
mathematical formula for how the peak of gene expression moves along
the PSM.
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