MicroRNA-independent functions of DGCR8 are critically required for neocortical development and TBR1 expression

Recent evidence indicates that DROSHA, DGCR8 and DICER exert non-overlapping functions, including miRNA-independent regulatory mechanisms. It is currently unknown whether miRNA-independent functions of DGCR8 play any role in corticogenesis. Here, by phenotypic comparison of conditional knockout cortices for Dgcr8 and Dicer, we uncover that Dgcr8 deletion, in contrast to Dicer, leads to premature differentiation of neural progenitor cells and overproduction of Tbr1 positive neurons. Remarkably, miRNA depletion does not account for these phenotypic differences, indicating that miRNA-independent functions of DGCR8 are critical for corticogenesis. We propose Tbr1 transcript, bearing evolutionary conserved hairpins that resemble miRNA precursors, as one of DGCR8 targets. Our study uncovers, for the first time in the nervous system, an earlier and stronger phenotype occurring in Dgcr8 compared to Dicer mutant and proposes that this effect is mediated by miRNA-independent functions of DGCR8. miRNA expression by deep-sequencing in the cortex of Wild-Type, DICER and DGCR8 conditional knock-out mice. Two mice for each genotype.最新研究证据表明，DROSHA（DROSHA）、DGCR8（DGCR8）与DICER（DICER）具备互不重叠的功能，其中包含不依赖于微小RNA（miRNA）的调控机制。目前尚不清楚DGCR8的不依赖miRNA的功能是否在皮质发生（corticogenesis）中发挥作用。本研究通过对Dgcr8与Dicer条件性基因敲除（conditional knockout）小鼠的大脑皮层进行表型比较，发现相较于Dicer敲除，Dgcr8缺失会导致神经祖细胞过早分化，并使Tbr1阳性神经元过量产生。值得注意的是，微小RNA耗竭无法解释这些表型差异，这提示DGCR8的不依赖miRNA的功能对皮质发生至关重要。我们提出，携带类似miRNA前体的进化保守发夹结构的Tbr1转录本，是DGCR8的靶标之一。本研究首次在神经系统中发现，相较于Dicer突变体，Dgcr8突变体呈现出出现更早、程度更显著的表型，并提出该效应是由DGCR8的不依赖miRNA的功能所介导的。本研究针对野生型（Wild-Type）、DICER条件性基因敲除及DGCR8条件性基因敲除小鼠的皮层组织开展了微小RNA深度测序（deep-sequencing）分析，每种基因型对应2只小鼠。