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) involved in establishing pattern in the mesoderm.
This current page has a number of research movies and animations that illustrate mesoderm development.
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 (More? abstract excerpt)
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)
Quicktime: presomitic mesoderm (256x256, 2.8 Mb)
Fate of the Somite (315Kb)
Vertebrae (366Kb)
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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. UNSW Embryology has many movies to show some of the dynamic changes that occur during embryonic development. These have been grouped together on separate pages (listed in righthand menu) that can be also be opened from a pull down menu on each page.
Internet users note that some of these movies are large and will take some time to download depending on your connection speed.
Both Mac and PC computers require the Quicktime plug-in to be present in your browser or on your computer.
CD users can find Quicktime on the CD or the latest version can be downloaded from here Quicktime
Please email Dr Mark Hill if you wish to make a comment about this current project.