- Keywords: extraocular muscles, regeneration, duchenne muscular dystrophy, contractility, omics
- Brief Description of the Project (maximum 3 paragraphs):
This research project investigates the cellular and genetic mechanisms that endow craniofacial muscles with specialized properties and resilience, particularly in the context of dystrophic and neurodegenerative diseases. Unlike trunk muscles, which primarily specialize in either force generation or endurance, craniofacial muscles perform highly intricate tasks essential for eye movements, feeding, and speech.
In this project, we will employ an integrative approach that combines advanced multiomics, spatial transcriptomics, and structural biology with physiological assessments. By selectively perturbing key gene expression programs during homeostasis and in pathological models, we aim to establish direct links between molecular determinants and muscle physiopathology
- Detailed Description of the Project :
Not all muscles in the body are equivalent. Extraocular muscles (EOMs), which control eye movement, are distinct from all other muscles due to their unique resistance to Duchenne muscular dystrophy and Amyotrophic lateral sclerosis and their remarkable evolutionary conservation across vertebrates in terms of muscle pattern and innervation modes (1–3). The coexistence of both vulnerable and resilient muscles within the same organism provides compelling in vivo evidence that sustained regenerative capacity is possible, even in severe conditions such as Duchenne muscular dystrophy. However, the mechanisms underlying EOM resilience remain largely unknown, making EOMs a powerful model for uncovering muscle-specific protective processes. Yet, significant gaps in our knowledge have hampered advancement in this field including the lack of molecular markers and functional readouts to score these properties.
Skeletal muscles in the head and trunk actually follow distinct developmental trajectories, a perspective our work has significantly advanced (4) . In particular we identified distinct transcription factors that govern cranial versus somite derived myogenesis potentially driving the enhanced proliferative capacity of adult cranial-derived stem cells in vitro and in vivo (5,6). Several other hypotheses have been proposed to explain EOM sparing in disease, including differences in developmental origin (non-somitic), cell metabolism, calcium handling. However, all these theories often assume a uniform protective mechanism, without fully considering the specific adaptations of EOM myofibers. Intriguingly, EOMs contain both singly and multiply innervated fibres, which are organized into different muscle layers and exhibit a broad spectrum of myosin heavy chain isoforms not present in any other muscle (7) . As a result, it remains unclear whether EOM resilience arises from a single overarching protective mechanism or from multiple fibre-specific adaptations that collectively enhance resistance to neuromuscular pathologies. Our preliminary work using single nuclear omics shows that EOMs feature remarkable transcriptional heterogeneity which correspond to functionally specialised subcompartments, and subsets of myofibres that harbor non-canonical muscle signatures. We hypothesize that this unique program may represent an ancient state of some skeletal muscles fibres and be required for unique mechanical functions.
This project aims to address the following key questions: What are the molecular basis of EOM myofibre specialisation and unique modes of sensory-motor control? Why are EOM myofibers more robust in neuromuscular disease?
- Scientific Objectives:
- Untangle the Functional Role of EOM fibre types: We have developed mouse mutant lines affecting specific EOM subcompartments, i.e. of the different muscle layers and harboring different types of innervation. We will link molecular programs in specialised myonuclei to sensory-motor coordination sensory-motor coordination through eye-tracking and visual acuity assessments (collaboration with NeuroPSi Paris Saclay) and address the impact of those contractile programs in dystrophic mouse models. Histological analysis and single molecule FISH will be used for a deep characterisation of the different mouse models.
- Assess the conservation of molecular program identified in the mouse in other species: Examining the conservation of EOM-specific molecular programs in primates and humans through immunohistochemistry and spatial transcriptomics, in collaboration with the Paris Brain Institute and Necker Hospital.
- Link molecular and structural myofibre features: Correlative light and electron microscopy and expansion microscopy will be used to reveal structural myofibre adaptations of EOM myofibres in both mouse and human.
Expected Impact (clinical or translational relevance): this project has to potential to achieve several conceptual breakthroughs: 1) uncover the molecular and structural features that confer EOMs with exquisite sensory-motor specialisation. These findings will be relevant to the medical fields of ophthalmology and strabismus surgery; 2) link EOM contractile properties to physiology and sparing in neuromuscular disease ; 3) provide a framework for developing refined strategies to confer other body muscles with protective mechanisms in disease. Altogether, this project promises to illuminate universal principles of musculoskeletal specialisation, with far reaching implications for regenerative medicine, disease modeling, and yield valuable knowledge on a variety of congenital craniofacial disorders and evolutionary processes.
- Expected Start Date: September 2025 (flexible)
- Is the project part of a consortium or collaboration? We are collaborating with V. Taglietti and E. Malfatti (Inst de recherche biomedicale Mondor, Créteil), Dr. M. Robert (Hopital Necker) and G. Bouvier (Sensomotion Lab, NeuroPsi, Paris-Saclay, France). We are also collaborating with in house platforms (EM, omics)
- Funding Source: Association Française for the myopathies grant for M2 students. Several grants have been submitted to obtain funding for PhD students. In parallel, applications to FRM and/or Pasteur-MD-PhD-PPU program will be also encouraged.
- Opportunities for Interdisciplinary Training: Depending on the candidate’s profile, specific training in bioinformatics and internships in the lab of our collaborators to develop specific skills will be envisaged.
Candidate Profile: We are looking for highly motivated and creative « Medicine-Sciences » students aiming to join the project for their M2 and/or PhD thesis. This internship is particularly suited for medical students with an interest in Neuromuscular disorders, Ophthalmology and vision sciences.
- We believe a multidisciplinary background in biology, hard sciences, and medicine is essential to tackle the questions of this projects, thereby bridging developmental biology to muscle physiology and clinical applications.
Specific Skills or Experience Required/Desirable: The project will involve experimental and computational work. The student will become familiar with a number of techniques routinely used in the lab including histology, confocal microscopy and image processing. Prior expertise in cell culture, image analysis and coding would be highly appreciated. Part of the work (Electron microscopy, eye movement testing, contractility) tests will be done in collaboration with specific platforms/partners. The candidate should feel comfortable working in English and be able to critically discuss experimental results and the literature. Students will be fully integrated in the scientific life of the lab and department (seminars, lab retreat, training).
Please send an email and cover letter to comai@pasteur.fr and shaht@pasteur.fr
1. Mercuri, E., Bönnemann, C. G. & Muntoni, F. Muscular dystrophies. Lancet 394, 2025–2038 (2019).
2. Domellöf, F. P. Amyotrophic Lateral Sclerosis – Recent Advances and Therapeutic Challenges. (2020). doi:10.5772/intechopen.89504
3. Suzuki, D. G. et al. Comparative morphology and development of extra-ocular muscles in the lamprey and gnathostomes reveal the ancestral state and developmental patterns of the vertebrate head. Zoological Letters 2, 10 (2016).
4. Grimaldi, A. & Tajbakhsh, S. Diversity in cranial muscles: Origins and developmental programs. Curr Opin Cell Biol 73, 110–116 (2021).
5. Girolamo, D. D. et al. Extraocular muscle stem cells exhibit distinct cellular properties associated with non-muscle molecular signatures. Development 151, (2024).
6. Grimaldi, A., Comai, G., Mella, S. & Tajbakhsh, S. Identification of bipotent progenitors that give rise to myogenic and connective tissues in mouse. Elife 11, e70235 (2022).
7. Hoh, J. F. Y. Developmental, Physiological and Phylogenetic Perspectives on the Expression and Regulation of Myosin Heavy Chains in Craniofacial Muscles. Int. J. Mol. Sci. 25, 4546 (2024).