Imaginal disc morphogenesis during metamorphosis in Drosophila melanogaster provides an excellent model to uncover molecular mechanisms by which hormonal signals effect physical changes during development. The broad (br) Z2 isoform encodes a transcription factor required for disc morphogenesis in response to 20-hydroxyecdysone, yet how it accomplishes this remains largely unknown. Here, we use functional studies of amorphic br⁵ mutants and a transcriptional target approach to identify processes driven by br and its regulatory targets in leg imaginal discs. br⁵ mutants fail to properly remodel their basal extracellular matrix (ECM) between 4 and 7 hours after puparium formation. Additionally, br⁵ mutant discs do not undergo the cell shape changes necessary for leg elongation and fail to elongate normally when exposed to the protease trypsin. RNA sequencing of wild type and br⁵ mutant leg discs identified 717 genes differentially regulated by br, including a large number of genes involved in glycolysis, and genes that encode proteins that interact with the ECM. RNAi-based functional studies reveal that several of these genes are required for adult leg formation, particularly those involved in remodeling the ECM. Additionally, br Z2 expression is abruptly shut down at the onset of metamorphosis, and expressing it beyond this time results in failure of leg development during the late prepupal and pupal stages. Taken together, our results suggest that br Z2 is required to drive ECM remodeling, change cell shape, and maintain metabolic activity through the mid prepupal stage, but must be switched off to allow expression of pupation genes.​.

中文翻译：

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广泛转录因子将果蝇成虫盘发育过程中的激素信号传导、基因表达和细胞形态发生事件联系起来。

果蝇变态过程中的成虫盘形态发生提供了一个很好的模型来揭示激素信号影响发育过程中物理变化的分子机制。Broad ( br ) Z2同种型编码椎间盘形态发生所需的转录因子，以响应 20-羟基蜕皮激素，但它如何实现这一目标仍然很大程度上未知。在这里，我们使用无定形br ⁵突变体的功能研究和转录靶点方法来识别由br驱动的过程及其在腿部成虫盘中的调节靶点。br ⁵突变体在蛹形成后 4 至 7 小时内无法正确重塑其基础细胞外基质 (ECM)。此外，br ⁵突变椎间盘不会经历腿伸长所需的细胞形状变化，并且当暴露于蛋白酶胰蛋白酶时无法正常伸长。对野生型和br ⁵突变体腿盘的 RNA 测序鉴定出br差异调节的 717 个基因，包括大量参与糖酵解的基因，以及编码与 ECM 相互作用的蛋白质的基因。基于 RNAi 的功能研究表明，其中一些基因是成人腿部形成所必需的，特别是那些参与 ECM 重塑的基因。此外，br Z2表达在变态开始时突然关闭，超过这个时间表达会导致在预蛹和蛹阶段的腿部发育失败。综上所述，我们的结果表明，br Z2是驱动 ECM 重塑、改变细胞形状并在蛹前中期维持代谢活动所必需的，但必须关闭以允许化蛹基因的表达。