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Morphological analysis of slow and fast muscle cells in zebrafish embryos

Orateurs :

André Khali, Department of Mathematics and Statistics, University of Maine, Orono, Maine

Salle :


Sujet :

The first part of the talk will be centered on muscle fiber formation. The cellular mechanisms that generate long muscle fibers from short cells and the molecular factors that limit elongation are unknown. We show that zebrafish muscle fiber morphogenesis consists of three discrete phases : protrusive activity, intercalation/elongation and boundary capture/myotube formation. Mathematical modeling indicates that intercalation proceeds via a two-step process. We find that laminin is required for efficient elongation, proper fiber orientation and boundary capture. Our results define three phases of muscle fiber morphogenesis and show that the critical second phase of elongation proceeds by a repetitive process of protrusion extension and protrusion filling. Furthermore, we show that laminin is a novel and critical molecular cue limiting muscle cell length.

In the second part of the talk, we will consider the effects of Fibronectin (Fn) as a major component of the extracellular matrix in both somite and myotome boundaries. Although Fn is required for somite boundary formation, effects of Fn disruption on muscle development are unknown. We show that Fn knockdown disrupts muscle morphogenesis. We also provide evidence that Fn plays a distinct role in muscle development outside of its role in somite formation. Slow-twitch fibers in Fn morphants are of irregular lengths and fast-twitch fibers are aberrantly long. Both qualitative and quantitative analyses indicate that these muscle phenotypes in Fn morphant embryos are distinct from a Notch pathway segmentation mutant, aei/deltaD. A wavelet-based anisotropy analysis shows that slow-twitch muscle fibers in Fn morphant embryos are more randomly structured than in wild-type and aei/deltaD mutant embryos, suggesting roles for Fn in initiating/maintaining slow-twitch muscle fiber structure. Fast-twitch fibers in Fn morphants are more likely to cross myotome boundaries than fast-twitch fibers in aei/deltaD mutant embryos. Taken together, these data suggest Fn may function to regulate slow-twitch fiber organization and limit fast-twitch muscle fiber length.

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