Skeletal muscles of the limb are derived from somites and their precursors migrate to the limb prior to muscle formation. Upon migration, a limited number of stem cells multiply and differentiate to give rise to fusion-competent muscle cells, which fuse to form the multinucleated myotubes. During the course of myogenesis there is thus a period of few days when cells at different developmental stages such as migrating, proliferating, differentiating and fully differentiated co-reside within the developing limb bud. Current understanding on how these cells interact and behave during early and later myogenesis in vivo is lacking. The aim of this project was to identify and further classify the mononucleated myogenic cells present within the developing limb muscle and examine their behaviours at different stages of myogenesis.
The lack of an appropriate method to extract and visualise cellular constituents of developing muscles has been a major limitation hindering such investigations in vivo. In this project, we first developed a unique cell isolation method to extract mononucleated cells from developing muscles, allowing examination of mononucleated cells in vivo using immunocytochemistry. As Pax3, Pax7 and Myogenic Regulatory Factors (MRFs) are the key players for the muscle formation, they were used to mark the different myogenic sub-populations.
The results from chicken and rats clearly demonstrate that three myogenic cell pools, namely Pax3, Pax7 and MRFs positive cells, and 4 sub-populations formed by their overlap, co-exist in specific proportions within the developing limb muscle, and that their proportions undergo dynamic changes during the course of myogenesis. The most striking observation was that the sizes of Pax3 and MRF compartments remain constant while that of Pax7 compartment increases dramatically during myogenesis. Thus each myogenic cell compartment in the developing muscle has different cell kinetics during primary and secondary myogenesis. The dynamic changes in the proportions of these myogenic sub-populations may constitute a dynamically maintained cellular niche, within which the muscle stem cells reside. Our study suggests that the concept of community effect - the interaction between a group of cells and their surrounding cells, originally from invertebrate muscle system, may be conserved in mammalian systems. Furthermore, this study for the first time, reports that the earliest fully differentiate muscle cells in the rat hindlimb are highly elongated mononucleated cells which express Pax3, MyoD, myogenin and myosin but not Myf-5 protein.
In summary, this study provides quantitative data to demonstrate dynamic changes in various mononucleated myogenic cell populations during skeletal muscle formation and reveals that Pax7(+ve) population becomes significantly upregulated during secondary myogenesis.
| Identifer | oai:union.ndltd.org:ADTP/217494 |
| Date | January 2007 |
| Creators | Lee, Antonio Seung Jin, n/a |
| Publisher | University of Otago. Department of Anatomy & Structural Biology |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Antonio Seung Jin Lee |
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