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Wnt signaling regulates the function of MyoD and myogenin
A G Ridgeway1, H Petropoulos, S Wilton
1Department of Biochemistry, Medical Sciences Building, University of Western Ontario, London, Ontario N6A 5C1, Canada.
Abstract:
The myogenic regulatory factors (MRFs), MyoD and myogenin, can induce myogenesis in a variety of cell lines but not efficiently in monolayer cultures of P19 embryonal carcinoma stem cells. Aggregation of cells expressing MRFs, termed P19[MRF] cells, results in an approximately 30-fold enhancement of myogenesis. Here we examine molecular events occurring during P19 cell aggregation to identify potential mechanisms regulating MRF activity. Although myogenin protein was continually present in the nuclei of >90% of P19[myogenin] cells, only a fraction of these cells differentiated. Consequently, it appears that post-translational regulation controls myogenin activity in a cell lineage-specific manner. A correlation was obtained between the expression of factors involved in somite patterning, including Wnt3a, Wnt5b, BMP-2/4, and Pax3, and the induction of myogenesis. Co-culturing P19[Wnt3a] cells with P19[MRF] cells in monolayer resulted in a 5- to 8-fold increase in myogenesis. Neither BMP-4 nor Pax3 was efficient in enhancing MRF activity in unaggregated P19 cultures. Furthermore, BMP-4 abrogated the enhanced myogenesis induced by Wnt signaling. Consequently, signaling events resulting from Wnt3a expression but not BMP-4 signaling or Pax3 expression, regulate MRF function. Therefore, the P19 cell culture system can be used to study the link between somite patterning events and myogenesis.
Insights
Cell aggregation significantly enhances myogenesis in P19 cells by regulating myogenic regulatory factors (MRFs). Wnt3a signaling, not BMP-4 or Pax3, drives this enhanced myogenesis, linking somite patterning to muscle development.
Area of Science:
- Muscle development and stem cell biology.
- Cell signaling pathways.
- Developmental biology.
Background:
- Myogenic regulatory factors (MRFs) like MyoD and myogenin are crucial for muscle formation.
- P19 embryonal carcinoma stem cells show inefficient myogenesis in monolayer cultures.
- Cell aggregation dramatically enhances myogenesis in P19[MRF] cells.
Purpose of the Study:
- To investigate molecular events during P19 cell aggregation that regulate MRF activity.
- To identify signaling pathways involved in MRF-mediated myogenesis.
- To explore the role of somite patterning factors in P19 cell differentiation.
Main Methods:
- Utilizing P19 embryonal carcinoma stem cells engineered to express MRFs (P19[MRF]), myogenin (P19[myogenin]), or Wnt3a (P19[Wnt3a]).
- Comparing myogenesis efficiency in aggregated versus monolayer cultures.
- Co-culturing different engineered P19 cell lines to assess signaling interactions.
- Analyzing the expression of somite patterning factors like Wnt3a, Wnt5b, BMP-2/4, and Pax3.
Main Results:
- Myogenin protein presence in nuclei does not guarantee differentiation, suggesting post-translational regulation of myogenin activity.
- Wnt3a expression correlates with enhanced myogenesis.
- Co-culturing P19[Wnt3a] and P19[MRF] cells in monolayer increases myogenesis 5- to 8-fold.
- BMP-4 and Pax3 do not enhance MRF activity in unaggregated cells, and BMP-4 inhibits Wnt-induced myogenesis.
Conclusions:
- Myogenin activity is regulated in a cell lineage-specific manner, likely through post-translational modifications.
- Wnt3a signaling, but not BMP-4 or Pax3, is a key regulator of MRF function in P19 cells.
- The P19 cell culture system provides a valuable model for studying the interplay between somite patterning and myogenesis.