دانلود رایگان مقاله اپیتلیوم روده در پوست اندازی کرم ابریشم

Abstract

The midgut of insects has attracted great attention as a system for studying intestinal stem cells (ISCs) as well as cell death-related processes, such as apoptosis and autophagy. Among insects, Lepidoptera represent a good model to analyze these cells and processes. In particular, larvaelarva molting is an interesting developmental phase since the larva must deal with nutrient starvation and its organs are subjected to rearrangements due to proliferation and differentiation events. Several studies have analyzed ISCs in vitro and characterized key factors involved in their division and differentiation during molt. However, in vivo studies performed during larvaelarva transition on these cells, and on the whole midgut epithelium, are fragmentary. In the present study, we analyzed the larval midgut epithelium of the silkworm, Bombyx mori, during larvaelarva molting, focusing our attention on ISCs. Moreover, we investigated the metabolic changes that occur in the epithelium and evaluated the intervention of autophagy. Our data on ISCs proliferation and differentiation, autophagy activation, and metabolic and functional activities of the midgut cells shed light on the complexity of this organ during the molting phase.

4.2. Metabolic characterization of the midgut epithelium

Starvation is a potent stress that, in the insect midgut, determines a series of events such as mobilization of stored metabolites (Satake et al., 2000), misregulation of metabolic enzyme activity (Ban, 1974), shortening of microvilli (Li et al., 2009), and activation of compensatory mechanisms such as autophagy (Khoa and Takeda, 2012). Since the functional activity of the midgut epithelium was partially reduced during the molting period, as discussed above, we investigated how metabolic activity within midgut cells is modified, in order to evaluate how they cope with starvation. To this aim we first analyzed the occurrence of autophagy in the epithelium. In fact, when the cell is subjected to nutrient deprivation, this cellular self-eating process can be activated to break down part of its reserves in order to stay alive until the situation improves (He and Klionsky, 2009). In insects, as well as in other animal models, autophagy has been shown to be rapidly induced when the organism undergoes structural remodeling, such as during metamorphosis, or when cells need to generate intracellular nutrients and energy, e.g., during starvation (Tettamanti et al., 2007b; Malagoli et al., 2010; Romanelli et al., 2014). For example, in Drosophila melanogaster, a few hours of nutrient starvation induces autophagy in larval organs (Scott et al., 2004)