Related Experiment Video
Updated: Jun 23, 2025
Isolation of Type I and Type II Pericytes from Mouse Skeletal Muscles
Published on: May 26, 2017
Interplay between Pitx2 and Pax7 temporally governs specification of extraocular muscle stem cells
Mao Kuriki1, Amaury Korb1, Glenda Comai1
1Institut Pasteur, Université Paris Cité, CNRS UMR 3738, Stem Cells & Development Unit, Institut Pasteur, Paris, France.
Abstract:
Gene regulatory networks that act upstream of skeletal muscle fate determinants are distinct in different anatomical locations. Despite recent efforts, a clear understanding of the cascade of events underlying the emergence and maintenance of the stem cell pool in specific muscle groups remains unresolved and debated. Here, we invalidated Pitx2 with multiple Cre-driver mice prenatally, postnatally, and during lineage progression. We showed that this gene becomes progressively dispensable for specification and maintenance of the muscle stem (MuSC) cell pool in extraocular muscles (EOMs) despite being, together with Myf5, a major upstream regulator during early development. Moreover, constitutive inactivation of Pax7 postnatally led to a greater loss of MuSCs in the EOMs compared to the limb. Thus, we propose a relay between Pitx2, Myf5 and Pax7 for EOM stem cell maintenance. We demonstrate also that MuSCs in the EOMs adopt a quiescent state earlier that those in limb muscles and do not spontaneously proliferate in the adult, yet EOMs have a significantly higher content of Pax7+ MuSCs per area pre- and post-natally. Finally, while limb MuSCs proliferate in the mdx mouse model for Duchenne muscular dystrophy, significantly less MuSCs were present in the EOMs of the mdx mouse model compared to controls, and they were not proliferative. Overall, our study provides a comprehensive in vivo characterisation of MuSC heterogeneity along the body axis and brings further insights into the unusual sparing of EOMs during muscular dystrophy.
Insights
Gene regulatory networks differ in skeletal muscles. Pitx2 is essential for muscle stem cells (MuSCs) in early development but becomes dispensable in adult extraocular muscles (EOMs), revealing a novel relay mechanism for EOM stem cell maintenance.
Area of Science:
- Developmental biology
- Stem cell biology
- Skeletal muscle physiology
Background:
- Gene regulatory networks controlling skeletal muscle stem cells (MuSCs) vary by anatomical location.
- The precise mechanisms governing MuSC pool emergence and maintenance in specific muscle groups are not fully understood.
Purpose of the Study:
- To investigate the role of Pitx2 in muscle stem cell (MuSC) specification and maintenance across different developmental stages and anatomical locations.
- To elucidate the regulatory network involving Pitx2, Myf5, and Pax7 in extraocular muscle (EOM) stem cell maintenance.
- To characterize the unique properties of MuSCs in EOMs compared to limb muscles, particularly in quiescent state, proliferation, and response to muscular dystrophy.
Main Methods:
- Utilized Cre-driver mouse models to achieve spatiotemporal inactivation of the Pitx2 gene during prenatal, postnatal, and lineage progression stages.
- Performed constitutive inactivation of Pax7 postnatally to assess its impact on MuSC populations in EOMs versus limb muscles.
- Analyzed MuSC content, proliferation status, and quiescent state in EOMs and limb muscles under normal conditions and in the mdx mouse model of Duchenne muscular dystrophy.
Main Results:
- Pitx2 is dispensable for adult EOM MuSC maintenance despite its crucial role alongside Myf5 in early development.
- Postnatal Pax7 inactivation caused a more pronounced loss of MuSCs in EOMs than in limb muscles.
- EOM MuSCs enter quiescence earlier, do not spontaneously proliferate in adults, and exhibit higher Pax7+ cell density, suggesting a distinct regulatory relay involving Pitx2, Myf5, and Pax7.
- EOMs in the mdx mouse model showed fewer MuSCs and reduced proliferation compared to controls, indicating an unusual sparing effect during muscular dystrophy.
Conclusions:
- A novel relay mechanism involving Pitx2, Myf5, and Pax7 is proposed for maintaining EOM stem cells.
- EOM MuSCs possess unique characteristics, including earlier quiescence and resistance to spontaneous proliferation, contributing to their distinct behavior.
- The study highlights significant heterogeneity in MuSC populations across the body axis and offers insights into the protective mechanisms of EOMs in muscular dystrophy.
