ABSTRACT
Animals’ coexistence with microbes has shaped their evolutionary history. In the bodies of vertebrates, the most abundant microbial community, or microbiota, resides in the digestive tract. Not only do these resident microbes play important functions in digestive physiology, but they modulate the developmental programs that give rise to the mature digestive tract. This chapter discusses research in the model vertebrate, the zebrafish, which sheds light on the impact of the microbiota on digestive tract development. The gnotobiotic zebrafish model provides examples of how innate immune sensing of microbial products establishes appropriate immune cell populations and tolerance of resident microbes. Innate immunity also modulates canonical developmental programs, such as Wnt and Notch signaling, to alter aspects of intestinal epithelial turnover and cell fate specification. In addition, secreted bacterial products can impact extraintestinal tissues, such as promoting expansion of insulin-producing beta cells in the pancreas. These examples demonstrate how modulation of tissue development in response to microbial cues contributes to vertebrate developmental plasticity and promotes animal fitness through adaptation to the host's environment.
