Amiri Ezra E, Tenger-Trolander Ayse, Li Muzi, Thomas Julian Alexander, Kasan Koray, Sanders Sheri A, Blythe Shelby, Schmidt-Ott Urs
The University of Chicago, Department of Organismal Biology and Anatomy, 1027 East 57 Street, Chicago, Illinois 60637, USA.
Illinois Institute of Technology, Department of Biology, 3105 South Dearborn Street, Chicago, Illinois 60616, USA.
bioRxiv. 2025 Jan 14:2025.01.13.632851. doi: 10.1101/2025.01.13.632851.
Establishing the anterior-posterior body axis is a fundamental process during embryogenesis, and the fruit fly, , provides one of the best-known case studies of this process. In Drosophila, localized mRNA of serves as anterior determinant (AD). Bicoid engages in a concentration-dependent competition with nucleosomes and initiates symmetry-breaking along the AP axis by promoting chromatin accessibility at the loci of transcription factor (TF) genes that are expressed in the anterior of the embryo. However, ADs of other fly species are unrelated and structurally distinct, and little is known about how they function. We addressed this question in the moth fly, , in which a maternally expressed transcript isoform of the pair-rule segmentation gene is localized in the anterior egg and has been co-opted as AD. We provide a assembly and annotation of the Clogmia genome and describe how knockdown of and maternal transcript affect chromatin accessibility and expression of TF-encoding loci. The results of these experiments suggest direct roles of Cal-Zld in opening and closing chromatin during nuclear cleavage cycles and show that Clogmia's maternal activity promotes chromatin accessibility and anterior expression during the early phase of zygotic genome activation at Clogmia's and loci. We conclude that unrelated dipteran ADs initiate anterior-posterior axis-specification at the level of enhancer accessibility and that and homologs may serve a more widely conserved role in the initiation of anterior pattern formation given their early anterior expression and function in head development in other insects.
建立前后体轴是胚胎发育过程中的一个基本过程，果蝇为此过程提供了最著名的案例研究之一。在果蝇中，bicoid的局部mRNA作为前部决定因子（AD）。Bicoid与核小体进行浓度依赖性竞争，并通过促进胚胎前部表达的转录因子（TF）基因位点的染色质可及性，启动沿前后轴的对称性破坏。然而，其他果蝇物种的AD是不相关的且结构不同，关于它们的功能知之甚少。我们在蕈蚊中解决了这个问题，在蕈蚊中，成对规则分割基因odd-paired的母体表达转录本异构体定位在前部卵中，并已被用作AD。我们提供了蕈蚊基因组的组装和注释，并描述了odd-paired和母体odd-paired转录本的敲低如何影响染色质可及性和TF编码位点的表达。这些实验结果表明，Cal-Zld在核分裂周期中打开和关闭染色质方面具有直接作用，并表明蕈蚊的母体odd-paired活性在合子基因组激活早期，在蕈蚊的odd-paired和hunchback位点促进染色质可及性和前部表达。我们得出结论，不相关的双翅目AD在增强子可及性水平上启动前后轴特化，并且odd-paired和hunchback同源物可能在其他昆虫头部发育中的早期前部表达和功能方面，在启动前部模式形成中发挥更广泛保守的作用。
