Choanoflagellates and the origin of animal morphogenesis
Morphogenesis is a universal dimension of animal embryonic development, and relies on a precisely controlled choreography of cell behaviors, such as controlled cell division, cell death, apical constriction, and controlled cell migration. While some of these cellular behaviors are known in single-celled eukaryotes, it is unknown how they first evolved, and how they were progressively assembled into the complex developmental cascades known in modern animals. As the sister-group of animals, choanoflagellates have the potential to inform the evolutionary origins of animal cell biology. Even though choanoflagellates have classically been known as flagellated cells with a fixed shape, I will report on two recent discoveries that have shown that choanoflagellate cell biology is much more plastic than previously assumed, in a way that suggests an unexpectedly ancient ancestry for animal morphogenetic mechanisms. First, collective cell contractility by apical constriction has also been recently discovered in a newly discovered colonial choanoflagellate isolated from a Caribbean island, that undergoes rapid and reversible whole-colony inversion in response to environmental stimuli (1). Second, we recently discovered that choanoflagellates subjected to spatial confinement undergo a rapid phenotypic switch from their canonical flagellate form to an amoeboid cell phenotype that resemble animal migratory cells in both structure and function (2). These two findings represent unexpected expansions of the known phenotypic repertoire of choanoflagellates and suggests a unicellular ancestry for apical constriction and epithelial-to-mesenchymal transitions.
1. T. Brunet et al., Science. 366, 326–334 (2019).
2. T. Brunet et al., Elife. 2021, e61037 (2021).
Institut Pasteur, Paris
Génétique et biologie du développement (UMR3215 / U934)