Movie is from supplementary material in the paper Masamizu Y, Ohtsuka T, Takashima Y, Nagahara H, Takenaka Y, Yoshikawa K, Okamura H, Kageyama R. Real-time imaging of the somite segmentation clock: revelation of unstable oscillators in the individual presomitic mesoderm cells. Proc Natl Acad Sci U S A. 2006 Jan 31;103(5):1313-8. Copyright (2006) National Academy of Sciences, U.S.A. Page also contains some modified text and images from this paper.
The movie shows real-time images of the presomitic mesoderm (PSM) expression of Hes1 (helix-loop-helix transcription factor) involved in Notch signaling for the somite segmentaion clock in a embryo (day 10.5). Images were taken over a period of 15 h, with oscillations propagated from the caudal end to S0 in the PSM. Movie © National Academy of Sciences (2006)
Note the changing distribution of this transcrition factor in "waves" from the caudal end of the embryo.
Quicktime: presomitic mesoderm (256x256, 2.8 Mb)
A single cycle of Hes 1 expression in presomitic mesoderm (click to enlarge)
Selected images from the Hes 1 expression movie
Masamizu Y, Ohtsuka T, Takashima Y, Nagahara H, Takenaka Y, Yoshikawa K, Okamura H, Kageyama R. Real-time imaging of the somite segmentation clock: revelation of unstable oscillators in the individual presomitic mesoderm cells. Proc Natl Acad Sci U S A. 2006 Jan 31;103(5):1313-8. Copyright (2006) National Academy of Sciences, U.S.A
"Notch signaling components such as the basic helix-loop-helix gene Hes1 are cyclically expressed by negative feedback in the presomitic mesoderm (PSM) and constitute the somite segmentation clock. .... the Hes1 oscillators in the individual PSM cells and fibroblasts are intrinsically similar, ...suggest that cell-cell communication is essential not only for synchronization but also for stabilization of cellular oscillators."
Thanks to Prof Ryoichiro Kageyama, Institute for Virus Research, Kyoto University, Kyoto 606-8507, Japan who provided this research movie on mesoderm development.
(Email: Prof R. Kageyama | Lab. of Growth Regulation | Institute for Virus Research)
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Mesoderm is a fascinationg layer of the trilaminar embryo, unlike ectoderm and endoderm which have an epithelial-like cellular organization, mesoderm layer appears initially to be a disorganised multilayer of cells.
Embryologists historically used the appearance of somites within the mesoderm layer as an accurate "clock" of early embryonic development. Classic chicken staging was by the number of somites present at a particular time. This led to the question of how this "clock" was actually leading to the pattern we observe being generated in the unsegemented presomitic mesoderm (PSM). Today we know some of the signaling processes (Notch and Wnt signaling) 1involved in establishing pattern in the mesoderm.
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