The silk gland is characterized by high protein synthesis. However, the molecular mechanisms controlling silk gland growth and silk protein synthesis remain undetermined. Here we demonstrated that CRISPR/Cas9-based knockdown of let-7 or the whole cluster promoted endoreduplication and enlargement of the silk gland, accompanied by changing silk yield, whereas transgenic overexpression of let-7 led to atrophy and degeneration of the silk gland. Mechanistically, let-7 controls cell growth in the silk gland through coordinating nutrient metabolism processes and energy signalling pathways. Transgenic overexpression of pyruvate carboxylase, a novel target of let-7, resulted in enlargement of the silk glands, which is consistent with the abnormal phenotype of the let-7 knockdown. Overall, our data reveal a previously unknown miRNA-mediated regulation of silk gland growth and physiology and shed light on involvement of let-7 as a critical stabilizer and booster in carbohydrate metabolism, which may have important implications for understanding of the molecular mechanism and physiological function of specialized organs in other species.

中文翻译：

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Let-7 microRNA是控制家蚕丝腺生长和功能的关键调节剂。

丝腺的特征在于高蛋白质合成。但是，控制丝腺生长和丝蛋白合成的分子机制仍未确定。在这里，我们证明了基于CRISPR / Cas9的let-7或整个簇的敲低促进了丝腺的核内复制和扩大，同时改变了丝产量，而let-7的转基因过表达导致了丝腺的萎缩和变性。从机制上讲，let-7通过协调营养代谢过程和能量信号传导途径来控制丝腺中的细胞生长。丙酮酸羧化酶（let-7的新靶标）的转基因过表达导致丝腺增大，这与let-7敲除的异常表型一致。总体，