Department of Molecular Cell and Developmental Biology, University of California Los Angeles, Los Angeles, CA 90095, USA.
Dev Genes Evol. 2011 Jun;221(2):69-81. doi: 10.1007/s00427-011-0360-x. Epub 2011 May 10.
The Drosophila larval and adult midguts are derived from two populations of endodermal progenitors that separate from each other in the early embryo. As larval midgut cells differentiate into an epithelial layer, adult midgut progenitors (AMPs) remain as small clusters of proliferating, undifferentiated cells attached to the basal surface of the larval gut epithelium. During the first few hours of metamorphosis, AMPs merge into a continuous epithelial tube that overgrows the larval layer and differentiates into the adult midgut; at the same time, the larval midgut degenerates. As shown in this paper, there is a second, transient pupal midgut that develops from the AMPs at the beginning of metamorphosis and that intercalates between the adult and larval midgut epithelia. Cells of the transient pupal midgut form a multilayered tube that exhibits signs of differentiation, in the form of septate junctions and rudimentary apical microvilli. Some cells of the pupal midgut develop as endocrine cells. The pupal midgut remains closely attached to the degenerating larval midgut cells. Along with these cells, pupal midgut cells are sequestered into the lumen where they form the compact "yellow body." The formation of a pupal midgut has been reported from several other species and may represent a general feature of intestinal metamorphosis in insects.
果蝇的幼虫和成虫中肠均由两个内胚层祖细胞群衍生而来，这两个细胞群在胚胎早期彼此分离。随着幼虫中肠细胞分化为上皮层，成虫中肠祖细胞（AMPs）仍作为附着在幼虫肠上皮基底表面的一小群增殖、未分化的细胞存在。在变态的最初几个小时内，AMPs 融合成一个连续的上皮管，该管覆盖在幼虫层上并分化为成虫中肠；同时，幼虫中肠退化。如本文所示，在变态开始时，AMPs 还会发育出第二个短暂的蛹期中肠，它位于成虫和幼虫中肠上皮之间。短暂的蛹期中肠的细胞形成一个具有多层结构的管，表现出分化的迹象，如隔膜连接和原始的顶端微绒毛。蛹期中肠的一些细胞发育成内分泌细胞。蛹期中肠仍紧密附着在退化的幼虫中肠细胞上。与这些细胞一起，蛹期中肠细胞被隔离到腔中，在那里它们形成密集的“黄色体”。已经从其他几个物种中报道了蛹期中肠的形成，这可能代表了昆虫肠道变态的一个普遍特征。
