Local retinoic acid signaling directs emergence of the extraocular muscle functional unit

PLoS Biol. 2020 Nov 17;18(11):e3000902. doi: 10.1371/journal.pbio.3000902. eCollection 2020 Nov.


Coordinated development of muscles, tendons, and their attachment sites ensures emergence of functional musculoskeletal units that are adapted to diverse anatomical demands among different species. How these different tissues are patterned and functionally assembled during embryogenesis is poorly understood. Here, we investigated the morphogenesis of extraocular muscles (EOMs), an evolutionary conserved cranial muscle group that is crucial for the coordinated movement of the eyeballs and for visual acuity. By means of lineage analysis, we redefined the cellular origins of periocular connective tissues interacting with the EOMs, which do not arise exclusively from neural crest mesenchyme as previously thought. Using 3D imaging approaches, we established an integrative blueprint for the EOM functional unit. By doing so, we identified a developmental time window in which individual EOMs emerge from a unique muscle anlage and establish insertions in the sclera, which sets these muscles apart from classical muscle-to-bone type of insertions. Further, we demonstrate that the eyeballs are a source of diffusible all-trans retinoic acid (ATRA) that allow their targeting by the EOMs in a temporal and dose-dependent manner. Using genetically modified mice and inhibitor treatments, we find that endogenous local variations in the concentration of retinoids contribute to the establishment of tendon condensations and attachment sites that precede the initiation of muscle patterning. Collectively, our results highlight how global and site-specific programs are deployed for the assembly of muscle functional units with precise definition of muscle shapes and topographical wiring of their tendon attachments.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Connective Tissue / physiology
  • Embryonic Development
  • Eye
  • Imaging, Three-Dimensional / methods
  • Mice / embryology
  • Mice, Inbred C57BL
  • Mice, Inbred DBA
  • Morphogenesis
  • Oculomotor Muscles / embryology*
  • Oculomotor Muscles / growth & development*
  • Signal Transduction
  • Tendons / physiology
  • Tretinoin / metabolism*
  • Tretinoin / physiology


  • Tretinoin

Grant support

We acknowledge funding support from the Institut Pasteur, Association Française contre le Myopathies, Agence Nationale de la Recherche (Laboratoire d’Excellence Revive, Investissement d’Avenir; ANR-10-LABX-73) and the Centre National de la Recherche Scientifique. We gratefully acknowledge the UtechS Photonic BioImaging (Imagopole), C2RT, Institut Pasteur, supported by the French National Research Agency (France BioImaging; ANR-10–INSB–04; Investments for the Future). MT, TZ and JK acknowledge the project CEITEC 2020 (LQ1601) with financial support from the Ministry of Education, Youth and Sports of the Czech Republic under the National Sustainability Programme II and Ceitec Nano+ project CZ.02.01/0.0./.0.0./16_013/0001728 under the program OP RDE. MT was financially supported by by the Brno City Municipality as a Brno Ph.D. Talent Scholarship Holder. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.