Lengyel Judith A, Iwaki D David
Department of Molecular, Cell, and Developmental Biology, University of California at Los Angeles, Los Angeles, California 90095-1606, USA.
Dev Biol. 2002 Mar 1;243(1):1-19. doi: 10.1006/dbio.2002.0577.
The Drosophila hindgut is fruitful territory for investigation of events common to many types of organogenesis. The development of the Drosophila hindgut provides, in microcosm, a genetic model system for studying processes such as establishment (patterning) of an epithelial primordium, its internalization by gastrulation, development of left--right asymmetric looping, patterning in both the anteroposterior and dorsoventral axes, innervation, investment of an epithelium with mesoderm, reciprocal epitheliomesenchymal interactions, cell shape change, and cell rearrangement. We review the genetic control of these processes during development of the Drosophila hindgut, and compare these to related processes in other bilaterians, particularly vertebrates. We propose that caudal/Cdx, brachyenteron/Brachyury, fork head/HNF-3, and wingless/Wnt constitute a conserved "cassette" of genes expressed in the blastopore and later in the gut, involved in posterior patterning, cell rearrangement, and gut maintenance. Elongation of the internalized Drosophila hindgut primordium is similar to elongation of the archenteron and also of the entire embryonic axis (both during and after gastrulation), as well as of various tubules (e.g., nephric ducts, Malpighian tubules), as it is driven by cell rearrangement. The genes drumstick, bowl, and lines (which encode putative transcriptional regulators) are required for this cell rearrangement, as well as for spatially localized gene expression required to establish the three morphologically distinct subregions of the hindgut. Expression of signaling molecules regulated by drumstick, bowl, and lines, in particular of the JAK/STAT activator Unpaired at the hindgut anterior, may play a role in controlling hindgut cell rearrangement. Other cell signaling molecules expressed in the hindgut epithelium are required to establish its normal size (Dpp and Hh), and to establish and maintain the hindgut visceral mesoderm (Wg and Hh). Both maternal gene activity and zygotic gene activity are required for asymmetric left--right looping of the hindgut. Some of the same genes (caudal and brachyenteron) required for embryonic hindgut development also act during pupation to construct a new hindgut from imaginal cells. Application of the plethora of genetic techniques available in Drosophila, including forward genetic screens, should identify additional genes controlling hindgut development and thus shed light on a variety of common morphogenetic processes.
果蝇后肠是研究多种器官发生共通事件的理想领域。果蝇后肠的发育，在微观层面上，为研究诸如上皮原基的建立（模式形成）、通过原肠胚形成实现其内化、左右不对称环化的发育、前后轴和背腹轴的模式形成、神经支配、中胚层对上皮的包裹、上皮与间充质的相互作用、细胞形状改变以及细胞重排等过程提供了一个遗传模型系统。我们回顾了果蝇后肠发育过程中这些过程的遗传控制，并将其与其他两侧对称动物，特别是脊椎动物中的相关过程进行比较。我们提出，尾型/Cdx、短肠/Brachyury、叉头/HNF-3和无翅/Wnt构成了一个保守的“基因盒”，这些基因在胚孔以及后来的肠道中表达，参与后部模式形成、细胞重排和肠道维持。内化的果蝇后肠原基的伸长类似于原肠的伸长，也类似于整个胚胎轴（在原肠胚形成期间和之后）以及各种小管（如肾管、马氏管）的伸长，因为它是由细胞重排驱动的。鼓槌、碗和线（编码假定的转录调节因子）基因对于这种细胞重排以及建立后肠三个形态学上不同的亚区域所需的空间定位基因表达是必需的。由鼓槌、碗和线调节的信号分子的表达，特别是后肠前部JAK/STAT激活剂未配对蛋白的表达，可能在控制后肠细胞重排中起作用。后肠上皮中表达的其他细胞信号分子对于确定其正常大小（Dpp和Hh）以及建立和维持后肠内脏中胚层（Wg和Hh）是必需的。后肠的不对称左右环化需要母源基因活性和合子基因活性。胚胎后肠发育所需的一些相同基因（尾型和短肠）在化蛹期间也起作用，从成虫盘细胞构建新的后肠。应用果蝇中可用的大量遗传技术，包括正向遗传筛选，应该能够鉴定出控制后肠发育的其他基因，从而阐明各种常见的形态发生过程。
