意大利蜜蜂胚后发育过程中中肠上皮组织细胞的更替

中肠是昆虫消化、 吸收营养物质的主要部位。本研究通过形态解剖、 BrdU免疫组织化学和原位末端转移酶标记(TUNEL)细胞凋亡检测等技术, 对意大利蜜蜂Apis mellifera ligustica中肠胚后发育过程中细胞的增殖和凋亡模式进行了比较研究。结果表明：意大利蜜蜂幼虫发育早期, 中肠的增加主要来自于上皮细胞的分裂以及再生细胞的增殖。在变态发育期间, 中肠上皮经历了广泛的重组, 由再生细胞重新形成的蛹上皮替代了幼虫上皮。再生细胞在蜜蜂中肠的整个发育阶段始终存在, 为中肠的生长和更替提供了主要的细胞来源。本研究为昆虫组织细胞自噬和凋亡机制的研究提供一定的证据。     

Degenerative and regenerative processes involved in midgut pseudotumor formation in the stick insect (Carausius morosus)

Spontaneous and experimentally induced pseudotumor formation in Carausius morosus impairs the midgut tissue homeostasis. Spontaneous pseudotumor formation begins by the break down of a single or a small group of columnar cells (CCs) and is followed by the degeneration of neighboring CCs. There are not only marked similarities but also decisive differences between normal dying CCs in healthy specimens and the degeneration of CCs leading to pseudotumors: in both cases, the apical cell parts with the nucleus are extruded into the midgut lumen, but only during of pseudotumor formation an “amorphous substance” originates from the basal parts of the CCs. Hemocytes are attracted to this substance and form a nodule‐like aggregation, which is responsible for the phenotype of pseudotumors. Pseudotumor infestation has also an impact on the midgut nidi, which consist of an intestinal stem cell and several CC progenitor cells. In healthy specimens only one progenitor cell per nidus differentiates at a time, but, several to all progenitor cells differentiate simultaneously in pseudotumor‐infested specimens. Extirpation of the ingluvial ganglion in healthy specimens results in an immediate onset of pseudotumor formation and a dramatic acceleration of pseudotumor growth. Importantly, the ultrastructural characteristics of spontaneous and experimentally induced pseudotumors are identical. This supports the idea that the stomatogastric nervous system plays an integral role in the maintenance of midgut tissue homeostasis. J. Morphol., 2009. © 2009 Wiley‐Liss, Inc.     

Intestinal stem cells in the adult Drosophila midgut

Drosophila has long been an excellent model organism for studying stem cell biology. Notably, studies of Drosophila's germline stem cells have been instrumental in developing the stem cell niche concept. The recent discovery of somatic stem cells in adult Drosophila, particularly the intestinal stem cells (ISCs) of the midgut, has established Drosophila as an exciting model to study stem cell-mediated adult tissue homeostasis and regeneration. Here, we review the major signaling pathways that regulate the self-renewal, proliferation and differentiation of Drosophila ISCs, discussing how this regulation maintains midgut homeostasis and mediates regeneration of the intestinal epithelium after injury.     

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.     

Infection of the European chafer,Amphimallon majalis by Bacillus popilliae: Light and electron microscope observations

Following ingestion of spores of Bacillus popilliae by grubs of the European chafer, Amphimallon majalis, vegetative rods were observed within phagocytic vacuoles of midgut columnar cells prior to establishing primary infection foci in regenerative nidi areas. This resulted in increased activity of regenerative nidi and extrusion of degenerating epithelial cells frequently containing vegetative rods of B. popilliae. Circulating hemocytes adhered to the hemocoelic surface of the basement membrane and formed inflammatory capsules immediately adjacent to the areas of bacterial proliferation. Bacilli in various stages of degradation were observed in membrane-limited vacuoles of both mesenteric epithelial cells and capsular hemocytes. Despite these host defense reactions, some vegetative cells resisted degradation and were successful in traversing the epithelial, basal lamina, and capsular barriers to enter the hemolymph.     

Control of life, death, and differentiation in cultured midgut cells of the lepidopteran, Heliothis virescens

Summary Differentiated cells in the insect midgut depend on stem cells for renewal. We have immunologically identified Integrin β₁, a promotor of cell-cell adhesion that also induces signals mediating proliferation, differentiation, and apoptosis on the surfaces of culturedHeliothis virescens midgut cells; clusters of immunostained integrin β₁-like material, indicative of activated integrin, were detected on aggregating midgut columnar cells. Growth factor-like peptides (midgut differentiation factors 1 and 2 [MDF1 and MDF2]), isolated from conditioned medium containingManduca sexta midgut cells, may be representative of endogenous midgut signaling molecules. Exposing the cultured midgut cells toBacillus thuringiensis (Bt) toxin caused large numbers of mature differentiated cells to die, but the massive cell death simultaneously induced a 150–200% increase in the numbers of midgut stem and differentiating cells. However, after the toxin was washed out, the proportions of cell types returned to near-control levels within 2 d, indicating endogenous control of cell-population dynamics. MDF1 was detected immunologically in larger numbers of Bt-treated columnar cells than controls, confirming its role in inducing the differentiation of rapidly produced stem cells. However, other insect midgut factors regulating increased proliferation, differentiation, as well as inhibition of proliferation and adjustment of the ratio of cell types, remain to be discovered. Products mentioned in this article are not endorsed by the U.S. Department of Agriculture.