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Delta 1-activated notch inhibits muscle differentiation without affecting Myf5 and Pax3 expression in chick limb
M C Delfini1, E Hirsinger, O Pourquié
1Institut d'Embryologie Cellulaire et Moléculaire du CNRS (FRE2160) et du Collège de France, 94736 Nogent sur Marne Cedex, France.
Abstract:
The myogenic basic helix-loop-helix (bHLH) transcription factors, Myf5, MyoD, myogenin and MRF4, are unique in their ability to direct a program of specific gene transcription leading to skeletal muscle phenotype. The observation that Myf5 and MyoD can force myogenic conversion in non-muscle cells in vitro does not imply that they are equivalent. In this paper, we show that Myf5 transcripts are detected before those of MyoD during chick limb development. The Myf5 expression domain resembles that of Pax3 and is larger than that of MyoD. Moreover, Myf5 and Pax3 expression is correlated with myoblast proliferation, while MyoD is detected in post-mitotic myoblasts. These data indicate that Myf5 and MyoD are involved in different steps during chick limb bud myogenesis, Myf5 acting upstream of MyoD. The progression of myoblasts through the differentiation steps must be carefully controlled to ensure myogenesis at the right place and time during wing development. Because Notch signalling is known to prevent differentiation in different systems and species, we sought to determine whether these molecules regulate the steps occurring during chick limb myogenesis. Notch1 transcripts are associated with immature myoblasts, while cells expressing the ligands Delta1 and Serrate2 are more advanced in myogenesis. Misexpression of Delta1 using a replication-competent retrovirus activates the Notch pathway. After activation of this pathway, myoblasts still express Myf5 and Pax3 but have downregulated MyoD, resulting in inhibition of terminal muscle differentiation. We conclude that activation of Notch signalling during chick limb myogenesis prevents Myf5-expressing myoblasts from progressing to the MyoD-expressing stage.
Insights
Myf5 and MyoD are key transcription factors in skeletal muscle development. This study reveals Myf5 acts upstream of MyoD, and Notch signaling prevents muscle differentiation by blocking progression from Myf5 to MyoD expression.
Area of Science:
- Developmental Biology
- Molecular Biology
- Cell Biology
Background:
- Myogenic basic helix-loop-helix (bHLH) transcription factors (Myf5, MyoD, myogenin, MRF4) drive skeletal muscle development.
- Myf5 and MyoD, while both myogenic, have distinct roles in myogenesis.
Purpose of the Study:
- To investigate the distinct roles of Myf5 and MyoD in chick limb development.
- To determine the involvement of Notch signaling in regulating chick limb myogenesis.
Main Methods:
- Analysis of Myf5 and MyoD transcript expression during chick limb development.
- Correlation of Myf5 and Pax3 expression with myoblast proliferation.
- Investigation of Notch signaling pathway activation via Delta1 misexpression.
Main Results:
- Myf5 transcripts appear before MyoD during chick limb development, with Myf5 expression domain larger and correlated with myoblast proliferation.
- MyoD is detected in post-mitotic myoblasts, indicating Myf5 acts upstream of MyoD.
- Notch signaling activation, induced by Delta1, leads to downregulation of MyoD and inhibition of terminal muscle differentiation, while Myf5 and Pax3 remain expressed.
Conclusions:
- Myf5 and MyoD are involved in distinct temporal steps of chick limb myogenesis, with Myf5 acting upstream of MyoD.
- Notch signaling activation prevents Myf5-expressing myoblasts from progressing to the MyoD-expressing stage, thereby inhibiting terminal muscle differentiation.