Damage‐induced regeneration of the intestinal stem cell pool through enteroblast mitosis in the Drosophila midgut

Many adult tissues and organs including the intestine rely on resident stem cells to maintain homeostasis and regeneration. In mammals, the progenies of intestinal stem cells (ISCs) can dedifferentiate to generate ISCs upon ablation of resident stem cells. However, whether and how mature tissue cells generate ISCs under physiological conditions remains unknown. Here, we show that infection of the Drosophila melanogaster intestine with pathogenic bacteria induces entry of enteroblasts (EBs), which are ISC progenies, into the mitotic cycle through upregulation of epidermal growth factor receptor (EGFR)‐Ras signaling. We also show that ectopic activation of EGFR‐Ras signaling in EBs is sufficient to drive enteroblast mitosis cell autonomously. Furthermore, we find that the dividing enteroblasts do not gain ISC identity as a prerequisite to divide, and the regenerative ISCs are produced through EB mitosis. Taken together, our work uncovers a new role for EGFR‐Ras signaling in driving EB mitosis and replenishing the ISC pool during fly intestinal regeneration, which may have important implications for tissue homeostasis and tumorigenesis in vertebrates.     

Intestinal stem cell proliferation and epithelial homeostasis in the adult Drosophila midgut

Adult tissue homeostasis requires a tight balance between the removal of old or damaged cells and the production of new ones. Such processes are usually driven by dedicated stem cells that reside within specific tissue locations or niches.The intestinal epithelium has a remarkable regenerative capacity, which has made it a prime paradigm for the study of stem cell-driven tissue self-renewal. The discovery of the presence of stem cells in the adult midgut of the fruit fly Drosophila melanogaster has significantly impacted our understanding of the role of stem cells in intestinal homeostasis. Here we will review the current knowledge of the main mechanisms involved in the regulation of tissue homeostasis in the adult Drosophila midgut, with a focus on the role of stem cells in this process. We will also discuss processes involving acute or chronic disruption of normal intestinal homeostasis such as damage-induced regeneration and ageing.     

Heparan sulfate maintains adult midgut homeostasis in Drosophila

Tissue homeostasis is controlled by the differentiated progeny of residential progenitors (stem cells). Adult stem cells constantly adjust their proliferation/differentiation rates to respond to tissue damage and stresses. However, how differentiated cells maintain tissue homeostasis remains unclear. Here, we find that heparan sulfate (HS), a class of glycosaminoglycan (GAG) chains, protects differentiated cells from loss to maintain intestinal homeostasis. HS depletion in enterocytes (ECs) leads to intestinal homeostasis disruption, with accumulation of intestinal stem cell (ISC)‐like cells and mis‐differentiated progeny. HS‐deficient ECs are prone to cell death/stress and induced cytokine and epidermal growth factor (EGF) expression, which, in turn, promote ISC proliferation and differentiation. Interestingly, HS depletion in ECs results in the inactivation of decapentaplegic (Dpp) signaling. Moreover, ectopic Dpp signaling completely rescued the defects caused by HS depletion. Together, our data demonstrate that HS is required for Dpp signal activation in ECs, thereby protecting ECs from ablation to maintain midgut homeostasis. Our data shed light into the regulatory mechanisms of how differentiated cells contribute to tissue homeostasis maintenance.     

食物营养对黑腹果蝇中肠干细胞的影响

【目的】研究市场上常见的几种儿童、青少年较为喜爱的小食品的主要营养成分,及其对黑腹果蝇Drosophila melanogaster的体重、发育等的影响,进而探讨膳食中营养均衡的重要性。【方法】采用双缩脲法、苏丹Ⅲ染色法及碘酒染色法分别对食物中的蛋白质、脂肪及淀粉含量进行测定。分别用基础培养基或实验用食品配制的培养基培养黑腹果蝇,待果蝇卵孵化后,取一定数量果蝇个体进行称重,并对果蝇中肠进行解剖和免疫荧光染色,观察果蝇肠道发育情况。【结果】基础食物(培养基)中的蛋白质、脂肪及淀粉含量配比较为均衡,而实验用零食有些脂肪含量较高,有些蛋白质含量较高,有些淀粉含量较高,配比严重失衡。淀粉及脂肪含量均较高的食物能引起果蝇体重超重;同时果蝇肠道细胞Arm/Pros的染色显著增加,显示肠道干细胞数目显著增加,另外果蝇肠壁明显加厚;而食物中淀粉或蛋白质严重缺失的食物则引起果蝇发育障碍。其中,在高碳水化合物但几乎没有蛋白质存在的食物中,果蝇干细胞数目同样增加很多,肠壁加厚,但其体重显著降低,同时发育迟缓。在高蛋白高脂肪低碳水化合物的食物中,中肠干细胞数目明显减少,果蝇肠壁变薄,发育受到影响。将几种实验组食物按照基础食物的蛋白质、脂肪及淀粉含量进行配比混合,模拟营养的均衡配比,喂养果蝇后发现,营养成分配比均衡极大地缓解配比失衡后所造成的中肠损伤,并使果蝇的个体发育恢复均衡。【结论】食物中的营养失衡会显著影响果蝇的体重以及肠壁和肠道干细胞的数目,导致果蝇体重下降或上升,肠道细胞增殖功能紊乱,对果蝇发育产生严重影响。这些结果提示了儿童偏好零食引起的营养不良和过度肥胖及肠道功能障碍,因此建议青少年儿童不能偏好零食,要做到合理膳食,营养均衡。     

The role of stem cells in midgut growth and regeneration

Summary TheManduca sexta (L.) [Lepidoptera: Sphingidae] andHeliothis virescens (F.) [Lepidoptera: Noctuidae] midguts consist of a pseudostratified epithelium surrounded by striated muscle and tracheae. This epithelium contains goblet, columnar, and basal stem cells. The stem cells are critically important in that they are capable of massive proliferation and differentiation. This growth results in a fourfold enlargement of the midgut at each larval molt. The stem cells are also responsible for limited cell replacement during repair. While the characteristics of the stem cell population vary over the course of an instar, stem cells collected early in an instar and those collected late can start in vitro cultures. Cultures of larval stem, goblet, and columnar cells survive in vitro for several mo through proliferation and differentiation of the stem cells. One of the two polypeptide differentiation factors which have been identified and characterized from the culture medium has now been shown to be present in midgut in vivo. Thus the ability to examine lepidopteran midgut stem cell growth in vitro and in vivo is proving to be effective in determining the basic features of stem cell action and regulation. Mention of any product in this publication does not imply endorsement by the USDA.     

Inducible progenitor-derived Wingless regulates adult midgut regeneration in Drosophila

The ability to regenerate following stress is a hallmark of self-renewing tissues. However, little is known about how regeneration differs from homeostatic tissue maintenance. Here, we study the role and regulation of Wingless (Wg)/Wnt signalling during intestinal regeneration using the Drosophila adult midgut. We show that Wg is produced by the intestinal epithelial compartment upon damage or stress and it is exclusively required for intestinal stem cell (ISC) proliferation during tissue regeneration. Reducing Wg or downstream signalling components from the intestinal epithelium blocked tissue regeneration. Importantly, we demonstrate that Wg from the undifferentiated progenitor cell, the enteroblast, is required for Myc-dependent ISC proliferation during regeneration. Similar to young regenerating tissues, ageing intestines required Wg and Myc for ISC hyperproliferation. Unexpectedly, our results demonstrate that epithelial but not mesenchymal Wg is essential for ISC proliferation in response to damage, while neither source of the ligand is solely responsible for ISC maintenance and tissue self-renewal in unchallenged tissues. Therefore, fine-tuning Wnt results in optimal balance between the ability to respond to stress without negatively affecting organismal viability.     

Tiny Drosophila intestinal stem cells,big power

The signaling pathways are highly conserved between Drosophila and mammals concerning intestinal development, regeneration, and disease. The powerful genetic tools of Drosophila make it a valuable and convenient alternative to answer basic biological questions that can not be addressed using mammalian models. In this review, we discuss recent advances in how we use fly midgut to answer the following key questions: (1) How intestine stem cell niches are established; (2) which factors control asymmetric division of stem cells; (3) how intestinal cells interact with environmental factors, such as tissue damage, microbiota, and diet; (4) how to screen aging/cancer-related factors or drugs by fly intestine stem cells.     

Intestinal stem cells and stem cell-based therapy for intestinal diseases

Currently, many gastrointestinal diseases are a major reason for the increased mortality rate of children and adults every year. Additionally, these patients may cope with the high cost of the parenteral nutrition (PN), which aids in the long-term survival of the patients. Other treatment options include surgical lengthening, which is not sufficient in many cases, and intestinal transplantation. However, intestinal transplantation is still accompanied by many challenges, including immune rejection and donor availability, which may limit the transplant’s success. The development of more safe and promising alternative treatments for intestinal diseases is still ongoing. Stem cell-based therapy (SCT) and tissue engineering (TE) appear to be the next promising choices for the regeneration of the damaged intestine. However, suitable stem cell source is required for the SCT and TE process. Thus, in this review we discuss how intestinal stem cells (ISCs) are a promising cell source for small intestine diseases. We will also discuss the different markers were used to identify ISCs. Moreover, we discuss the dominant Wnt signaling pathway in the ISC niche and its involvement in some intestinal diseases. Additionally, we discuss ISC culture and expansion, which are critical to providing enough cells for SCT and TE. Finally, we conclude and recommend that ISC isolation, culture and expansion should be considered when SCT is a treatment option for intestinal disorders. Therefore, we believe that ISCs should be considered a cell source for SCT for many gastrointestinal diseases and should be highlighted in future clinical applications.     

果蝇干细胞研究进展

本文主要介绍了果蝇五种干细胞,包括生殖干细胞、神经干细胞、造血干细胞、小肠干细胞、肾干细胞及其微环境（niche）的组成成份;简述了五种干细胞系统对应的分子标记;最后重点介绍了调控每种干细胞系统的信号通路。     

Disruption of EGF Feedback by Intestinal Tumors and Neighboring Cells in Drosophila

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Intestinal stem cells and intestinal organoids

The intestinal epithelium is one of the most rapidly renewing tissues, which is fueled by stem cells at the base of the crypts. Strategies of genetic lineage tracing and organoids, which capture major features of original tissues, are powerful avenues for exploring the biology of intestinal stem cells in vivo and in vitro,respectively. The combination of intestinal organoideculturing system and genetic modification approaches provides an attractive platform to uncover the mechanism of colorectal cancer and genetic disorders in the human minigut. Here, we will provide a comprehensive overview of studies on intestinal epithelium and intestinal stem cells. We will also review the applications of organoids and genetic markers in intestinal research studies. Furthermore, we will discuss the advantages and drawbacks of organoids as disease models compared with mice models and cell lines.     

Increased centrosome amplification in aged stem cells of the Drosophila midgut

Age-related changes in long-lived tissue-resident stem cells may be tightly linked to aging and age-related diseases such as cancer. Centrosomes play key roles in cell proliferation, differentiation and migration. Supernumerary centrosomes are known to be an early event in tumorigenesis and senescence. However, the age-related changes of centrosome duplication in tissue-resident stem cells in vivo remain unknown. Here, using anti-γ-tubulin and anti-PH3, we analyzed mitotic intestinal stem cells with supernumerary centrosomes in the adult Drosophila midgut, which may be a versatile model system for stem cell biology. The results showed increased centrosome amplification in intestinal stem cells of aged and oxidatively stressed Drosophila midguts. Increased centrosome amplification was detected by overexpression of PVR, EGFR, and AKT in intestinal stem cells/enteroblasts, known to mimic age-related changes including hyperproliferation of intestinal stem cells and hyperplasia in the midgut. Our data show the first direct evidence for the age-related increase of centrosome amplification in intestinal stem cells and suggest that the Drosophila midgut is an excellent model for studying molecular mechanisms underlying centrosome amplification in aging adult stem cells in vivo.     

The Drosophila ovary: an active stem cell community

Only a small number of cells in adult tissues (the stem cells) possess the ability to self-renew at every cell division,while producing differentiating daughter cells to maintain tissue homeostasis for an organism's lifetime.The Drosophilaovary harbors three different types of stem cell populations (germline stem cell (GSC),somatic stem cell (SSC) andescort stem cell (ESC)) located in a simple anatomical structure known as germarium,rendering it one of the best modelsystems for studying stem cell biology due to reliable stem cell identification and available sophisticated genetic toolsfor manipulating gene functions.Particularly,the niche for the GSC is among the first and best studied ones,and studieson the GSC and its niche have made many unique contributions to a better understanding of relationships between stemcells and their niche.So far,both the GSC and the SSC have been shown to be regulated by extrinsic factors originatingfrom their niche and intrinsic factors functioning within.Multiple signaling pathways are required for controlling GSCand SSC self-renewal and differentiation,which provide unique opportunities to investigate how multiple signals fromthe niche are interpreted in the stem cell.Since the Drosophila ovary contains three types of stem cells,it also providesoutstanding opportunities to study how multiple stem cells in a given tissue work collaboratively to contribute to tissuefunction and maintenance.This review highlights recent major advances in studying Drosophila ovarian stem cells andalso discusses future directions and challenges.     

小分子RNA决定果蝇生殖干细胞命运的分子机制研究

生殖干细胞是具有自我更新能力的一群生殖细胞,充当配子生成的源泉。果蝇生殖干细胞的特征在于通过不对称分裂产生两个子代细胞,一个通过自我更新维持干细胞特性,另一个则进行分化。生殖干细胞的命运受其周围的微环境——"干细胞niche"控制,而"niche"的功能又通过干细胞的外源和内源信号间的相互作用来完成。小分子RNA通过复杂的RNAi途径调控基因的表达。大量证据表明生殖干细胞的维持和分化需要小分子RNA参与,小分子RNA生成的紊乱会导致干细胞的"丢失"或"未分化"。该文综述了小分子RNA对果蝇生殖干细胞命运调控的研究进展,并讨论新发现的小分子RNA在生殖干细胞命运决定中的相关功能。     

Role of integrin beta1-like protein in proliferation and differentiation of cultured stem cells from midgut of Heliothis virescens

Cultured midgut cells from Heliothis virescens larvae were incubated with anti-human integrin beta1 made in rabbit and then passed over a column of magnetic beads bound to anti-rabbit IgG (MACS, Miltenyi Bergisch Gladbach, Germany). Cells bound to integrin beta1 antibody also bound to the anti-rabbit IgG on the magnetic beads (MACS) and were retained in the column while it remained in the magnetic field. Non-bound cells were eluted at this time. They did not stain with anti-integrin antibody just after elution. Removing the column from the magnetic field allowed cells bound to the beads-integrin beta1 antibody to be eluted. All of these cells stained with human anti-integrin beta1 upon elution. Each cell fraction was cultured in medium for 3 days. During this time, the populations of cells tended to return to heterogeneous staining patterns characteristic of control populations. However, cells that did not stain immediately with anti-integrin beta1 antibody exhibited double the rate of multiplication and 8 times more differentiation than the integrin-antibody positive cells that eluted later, as well as the non-treated control cells. In a second experiment, midgut cells were incubated for 4 days with various titers of human anti-integrin beta1 to block surface integrin beta1-like reactive sites. Stem cells blocked with anti-integrin beta1 antibody during incubation exhibited double the rate of differentiation than non-treated control cells and those showing anti-integrin beta1-positive stain upon elution.     

The fine structural morphology of the midgut of adult Drosophila: A morphometric analysis

The midgut of one day old Drosophilia was examined morphometrically at the electron microscopic level. Results suggest that parenchymal cells, with the exception of basal cells, possess identical functions. Drosophilia midgut cells are smaller than those of other insects studied, and the surface densities of the rER was less, indicating that its protein synthetic activity is also less than that of other insects.