Interestingly, with the exception of the large flat cell (LFC) region (LFCR) and Fe cell region (FCR), ISCs do not cross regional boundaries after division (termed non-crossing behavior) [28], but it is not clear how this occurs. remarkable series of recent findings in the literature to decipher the molecular mechanisms through which stem cells respond to nonsterile environments. is an excellent model Zonampanel system, due in large part to the ease of its genetic manipulation, that allows researchers to investigate prolonged intestinal inflammation and Rabbit polyclonal to ABCA3 damage. The proliferative activity of a dedicated population of intestinal stem cells (ISCs) is instigated by a multitude of stresses and ensures the control of remarkably rapid cell renewal [1, 2]. Thus, to function efficiently, the adult gastrointestinal tract possesses tools to maintain homeostasis and organismal health [3C6]. As recently established by a growing body of literature, these tools comprise a range of critical intestinal defense strategies, the dysregulation of which provokes the breakdown of intestinal homeostasis and precipitates or aggravates gastrointestinal diseases. (1) The intestinal lumen is lined by the peritrophic membrane, which represents the first line of host defense against invasion by enteric pathogens [7, 8]. (2) Rapid reactive oxide species (ROS) bursts, which are directly microbicidal, are triggered in epithelial cells following the ingestion of pathogens [9]. (3) In epithelial cells, Relish/NF-B-dependent antimicrobial peptides (AMPs) are believed to act as a second line of defense for killing pathogens [10C14]. (4) The epithelial lining is rapidly regenerated in response to pathogens to maintain homeostasis [15]. ISCs that undergo mitosis give rise to differentiated cells and are responsible for a range of critical intestinal functions [16, 17]. Over decades of intensive study, research investigating the cues governing epithelial regenerative homeostasis has progressed. The ultimate goal of our review is to position recent discoveries within the context of how stem cells in the adult gastrointestinal tract respond to environmental challenges. Review The adult gastrointestinal tract: A comprehensive overview Sequential organizationFirst, this review will introduce the adult gut architecture. The anatomical details of the adult gastrointestinal tract are relatively well known. It comprises a tubular epithelium consisting of three discrete domains with different developmental origins, cell types and physiological functions: the foregut, the midgut and the hindgut (Fig. ?(Fig.1Aa)1Aa) [18C20]. (1) The foregut, which is lined by the impermeable cuticle, is derived from the embryonic ectoderm and is responsible for the transport and storage of ingested food [16, 21]. (2) The midgut, which absorbs nutrients, is of endodermal origin and is subdivided into three domains based on longitudinal pH gradients (Fig. ?(Fig.1Ab)1Ab) [22]: the neutral segment, termed the anterior midgut (AM); the short and narrow middle midgut (MM) segment, which contains the copper cell region (CCR); and the wider, alkaline posterior midgut (PM), which has been the focus of a series of functional studies due to its physiological equivalence Zonampanel to the human small intestine. Further divisions of the AM and the PM are shown in Fig. ?Fig.1Ac.1Ac. (3) Reabsorption of water and the elimination of undigested waste are the responsibilities of the embryonic ectoderm-derived hindgut [21], which contains the pylorus, ileum and rectum. Additionally, the osmoregulatory and excretory apparatuses are the hindgut primordium and visceral mesoderm-derived Malpighian tubules (MTs), from which waste is released from the surrounding hemolymph into the gut lumen [23C26]. The MTs Zonampanel consist of the ureter, lower tubule and upper tubule [24]. Open in a separate window Fig. 1 Atlases of sequential compartments. (Aa) Three discrete domains are defined: the FG, the MG and the HG. (Ab) The MG is divided into the AM, the MM and the PM. (Ac) The AM comprises the AAM and PAM; the PM comprises the APM and PPM. (Ad, Ae) Subdivisions (R0-R5 and A1-P4) are established. (Af) Thirteen subregions ranging from R1a to R5b represent the fine-grained compartmentalization of R0-R5. (B) The close correspondence between R0-R5 and A1-P4. BR3-R4 indicates the boundary of R3-R4. For example, R2 comprises A2 and A3 (Ba, Ba), and A2 comprises R2a and R2b (Bb, Bb) The long-term maintenance of the integrity of the intestinal subregions is strongly associated with specialized physiological roles, the abnormal adjustment of which is characterized by a widespread loss of intestinal homeostasis. Thus, we next discuss current knowledge of the regionalization of.