The helicase domain of Dicer ensures essential accuracy of miRNA biogenesis in mice. The helicase domain of Dicer ensures essential accuracy of miRNA biogenesis in mice

Dicer ribonucleases, which generate small RNAs for the RNA interference (RNAi) and microRNA (miRNA) pathways, often have an N-terminal DExD helicase subdomain (also called HEL1). In the mammalian Dicer, HEL1 inhibits RNAi while it appears unnecessary for miRNA biogenesis. To determine its functional significance, we genetically eliminated HEL1 from Dicer in mice. We observed embryonic growth retardation, defects in the cardiopulmonary system, and perinatal lethality. HEL1 suppresses biogenesis of mirtrons, a non-canonical low-abundant class of miRNAs, and is required for high-fidelity cleavage and strand selection during biogenesis of canonical miRNAs. The HEL1 domain itself is essential rather than its helicase activity, because mutations of critical catalytic amino acids do not affect mouse viability or fertility and have minimal impact on miRNA biogenesis. Therefore, HEL1 is a critical structural component of the mammalian Dicer, supporting its role of a conserved structural “mold” that ensures high-fidelity processing and adaptive evolution of mammalian miRNA precursors. Overall design: Bulk small RNA-seq of 6 mouse E15.5 embryo samples: - 3x WT - 3x DicerGNT homozygotes

Dicer核糖核酸酶可生成用于RNA干扰（RNA interference, RNAi）与微小RNA（microRNA, miRNA）通路的小RNA，其通常携带N端DExD解旋酶结构域（亦称为HEL1）。在哺乳动物Dicer蛋白中，HEL1会抑制RNAi通路，但对miRNA的生物发生过程似乎并非必需。为明确其功能意义，我们在小鼠体内通过遗传学手段敲除了Dicer中的HEL1结构域。实验观察到胚胎发育迟缓、心肺系统缺陷以及围产期致死表型。HEL1可抑制mirtrons——一类非经典低丰度miRNA类群——的生物发生，同时在经典miRNA的生物发生过程中，对高保真切割与链选择至关重要。HEL1结构域本身是功能性必需的，而非其解旋酶活性：关键催化氨基酸的突变既不会影响小鼠的存活能力与生育能力，也对miRNA的生物发生仅存在微弱影响。因此，HEL1是哺乳动物Dicer的关键结构组分，作为保守的结构"模具"发挥作用，保障哺乳动物miRNA前体的高保真加工与适应性进化。
整体实验设计：对6份小鼠E15.5胚胎样本开展批量小RNA测序（small RNA-seq）：
- 3份野生型（WT）样本
- 3份DicerGNT纯合子样本