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量化背核梯度成像揭示了果蝇中基于阈值的模式形成的局限性。

Quantitative imaging of the Dorsal nuclear gradient reveals limitations to threshold-dependent patterning in Drosophila.

机构信息

Division of Biology, California Institute of Technology, 1200 East California Boulevard, MC114-96, Pasadena, CA 91125, USA.

出版信息

Proc Natl Acad Sci U S A. 2009 Dec 29;106(52):22317-22. doi: 10.1073/pnas.0906227106. Epub 2009 Dec 16.

Abstract

The NF-kappaB-related transcription factor, Dorsal, forms a nuclear concentration gradient in the early Drosophila embryo, patterning the dorsal-ventral (DV) axis to specify mesoderm, neurogenic ectoderm, and dorsal ectoderm cell fates. The concentration of nuclear Dorsal is thought to determine these patterning events; however, the levels of nuclear Dorsal have not been quantified previously. Furthermore, existing models of Dorsal-dependent germ layer specification and patterning consider steady-state levels of Dorsal relative to target gene expression patterns, yet both Dorsal gradient formation and gene expression are dynamic. We devised a quantitative imaging method to measure the Dorsal nuclear gradient while simultaneously examining Dorsal target gene expression along the DV axis. Unlike observations from other insects such as Tribolium, we find the Dorsal gradient maintains a constant bell-shaped distribution during embryogenesis. We also find that some classical Dorsal target genes are located outside the region of graded Dorsal nuclear localization, raising the question of whether these genes are direct Dorsal targets. Additionally, we show that Dorsal levels change in time during embryogenesis such that a steady state is not reached. These results suggest that the multiple gene expression outputs observed along the DV axis do not simply reflect a steady-state Dorsal nuclear gradient. Instead, we propose that the Dorsal gradient supplies positional information throughout nuclear cycles 10-14, providing additional evidence for the idea that compensatory combinatorial interactions between Dorsal and other factors effect differential gene expression along the DV axis.

摘要

NF-κB 相关转录因子 Dorsal 在早期果蝇胚胎中形成核浓度梯度,对背腹(DV)轴进行图案化,以指定中胚层、神经发生外胚层和背侧外胚层细胞命运。核 Dorsal 的浓度被认为决定了这些图案形成事件;然而,核 Dorsal 的水平以前没有被量化。此外,现有的 Dorsal 依赖性胚层特化和模式形成模型考虑了相对于靶基因表达模式的 Dorsal 的稳态水平,但 Dorsal 梯度形成和基因表达都是动态的。我们设计了一种定量成像方法来测量 Dorsal 核梯度,同时检查 DV 轴上 Dorsal 靶基因的表达。与其他昆虫(如 Tribolium)的观察结果不同,我们发现 Dorsal 梯度在胚胎发生过程中保持恒定的钟形分布。我们还发现一些经典的 Dorsal 靶基因位于分级 Dorsal 核定位区域之外,这提出了这些基因是否是 Dorsal 的直接靶基因的问题。此外,我们表明 Dorsal 水平在胚胎发生过程中随时间变化,因此没有达到稳定状态。这些结果表明,沿 DV 轴观察到的多个基因表达输出并不仅仅反映了稳态 Dorsal 核梯度。相反,我们提出 Dorsal 梯度在核循环 10-14 期间提供位置信息,为 Dorsal 和其他因子之间的补偿组合相互作用沿 DV 轴影响差异基因表达的观点提供了额外的证据。

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