Good genes, good food, good friends. That is what parents hope will sustain and nurture the harmonious growth of their children. The impact of the genetic background and nutrition on postnatal growth has been in the spot light for long, but the good friends have come to the scene only recently. Among the good friends perhaps the most crucial ones are those that we are carrying within ourselves. They comprise the trillions of microbes that collectively constitute each individual's intestinal microbiota. Indeed, recent epidemiological and field studies in humans, supported by extensive experimental data on animal models, demonstrate a clear role of the intestinal microbiota on their host's juvenile growth, especially under suboptimal nutrient conditions. Genuinely integrative approaches applicable to invertebrate and vertebrate systems combine tools from genetics, developmental biology, microbiology, nutrition, and physiology to reveal how gut microbiota affects growth both positively and negatively, in healthy and pathological conditions. It appears that certain natural or engineered gut microbiota communities can positively impact insulin/IGF-1 and steroid hormone signaling, thus contributing to the host juvenile development and maturation.

INSERM U1059 Sainbiose Université de Lyon Université Jean Monnet Faculté de Médecine Campus Santé Innovation 42023 Saint Étienne France

Institut de Génomique Fonctionnelle de Lyon Université de Lyon Ecole Normale Supérieure de Lyon CNRS UMR 5242 Université Claude Bernard Lyon 1 69364 Lyon Cedex 07 France

Laboratory of Gnotobiology Institute of Microbiology of the Czech Academy of Sciences Nový Hrádek Czech Republic

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Gut microbe Lactiplantibacillus plantarum undergoes different evolutionary trajectories between insects and mammals