转录本长度调节果蝇基因表达的发育时间
Transcript length mediates developmental timing of gene expression across Drosophila
摘要：
转录具有长初级转录物的基因所需的时间可能限制它们在具有短有丝分裂周期的细胞中表达的能力，这种现象称为内含子延迟。由于如此短的周期是昆虫发育最早阶段的标志，我们使用果蝇发育时程表达数据来测试内含子延迟是否影响全基因组的基因表达，并确定其对基因结构进化的影响。我们发现，长合子表达，但不是母系沉积，基因表现出相当大的延迟表达相对于其较短的对应物，这种延迟持续了相当大的一部分的胚胎发生的~24小时。从转录物的5'和3'末端的RNA-seq覆盖的模式显示，这种延迟与它们不能终止转录一致，但与基于转录起始的调控控制不一致。高度表达的合子基因受到纯化选择以保持紧凑的转录区域，从而允许在果蝇胚胎发育中保存胚胎表达模式。我们建议，内含子延迟是一个未被充分认识的物理机制，影响两种模式的表达，以及整个果蝇的许多基因的基因结构。
英文摘要：
The time required to transcribe genes with long primary transcripts may limit their ability to be expressed in cells with short mitotic cycles, a phenomenon termed intron delay. As such short cycles are a hallmark of the earliest stages of insect development, we used Drosophila developmental timecourse expression data to test whether intron delay affects gene expression genome-wide, and to determine its consequences for the evolution of gene structure. We find that long zygotically expressed, but not maternally deposited, genes show substantial delay in expression relative to their shorter counterparts and that this delay persists over a substantial portion of the ~24 hours of embryogenesis. Patterns of RNA-seq coverage from the 5' and 3' ends of transcripts show that this delay is consistent with their inability to terminate transcription, but not with transcriptional initiation-based regulatory control. Highly expressed zygotic genes are subject to purifying selection to maintain compact transcribed regions, allowing conservation of embryonic expression patterns across the Drosophila phylogeny. We propose that intron delay is an underappreciated physical mechanism affecting both patterns of expression as well as gene structure of many genes across Drosophila.
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