Temporal gene expression changes and affected pathways in neurodevelopment of a mouse model of Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome is an autosomal recessive disorder that arises from mutations in the gene DHCR7, which encodes the terminal enzyme of cholesterol biosynthesis, leading to decreased production of cholesterol and accumulation of the cholesterol precursor, 7-dehydrocholesterol, and its oxysterol metabolites. The disorder displays a wide range of neurodevelopmental defects, intellectual disability and behavioral problems. However, an in-depth study on the temporal changes of gene expression in the developing brains of SLOS mice has not been done before. In this work, we carried out the transcriptomic analysis of whole brains from WT and Dhcr7-KO mice at four time points through postnatal day 0. First, we observed the expected downregulation of the Dhcr7 gene in the Dhcr7-KO mouse model, as well as gene expression changes of several other genes involved in cholesterol biosynthesis throughout all time points. Pathway and GO term enrichment analyses revealed affected signaling pathways and biological processes that were shared amongst time points and unique to individual time points. Specifically, the pathways important for embryonic development, including Hippo, Wnt, and TGF-β signaling pathways are the most significantly affected at the earliest time point, E12.5. Additionally, neurogenesis-related GO terms were enriched in earlier time points, consistent with the timing of development. Conversely, pathways related to synaptogenesis, which occurs later in development compared to neurogenesis, are significantly affected at the later time points, E16.5 and PND0, including the cholinergic, glutamatergic, and GABAergic synapses. The impact of these transcriptomic changes and enriched pathways is discussed in the context of known biological phenotypes of SLOS. Total RNA was sequenced for four replicates each of whole brains from WT and Dhcr7-KO mouse embryos/neonates at four different gestational time points, including three embryonic (E12.5, E14.5, and E16.5) and one postnatal time point (PND0).史密斯-莱姆利-奥皮茨综合征（Smith-Lemli-Opitz syndrome, SLOS）是一种常染色体隐性遗传病，由DHCR7基因的突变引发。该基因编码胆固醇生物合成通路的末端酶，其突变会导致胆固醇合成减少，并使胆固醇前体7-脱氢胆固醇（7-dehydrocholesterol）及其氧固醇代谢物发生蓄积。该疾病表现出广泛的神经发育缺陷、智力障碍与行为异常。然而，此前尚未有针对SLOS小鼠模型发育大脑中基因表达时序变化的深入研究。本研究对野生型（Wild Type, WT）与Dhcr7基因敲除（Dhcr7 knockout, Dhcr7-KO）小鼠的全脑，在四个涵盖胚胎期至出生后0天的时间点开展了转录组分析：四个时间点具体包括三个胚胎期（E12.5、E14.5、E16.5）与一个出生后时间点（PND0），每组样本均设置四个生物学重复，对其全脑总RNA进行测序。研究首先观察到Dhcr7-KO小鼠模型中Dhcr7基因的预期下调现象，同时发现在所有时间点中，其他多个参与胆固醇生物合成的基因均出现表达变化。通路与基因本体（Gene Ontology, GO）术语富集分析显示，存在各时间点共有的、以及各时间点特有的受影响信号通路与生物学过程。具体而言，对胚胎发育至关重要的通路，包括Hippo、Wnt及转化生长因子-β（Transforming Growth Factor-β, TGF-β）信号通路，在最早的时间点E12.5时受影响最为显著。此外，与神经发生相关的GO富集项在早期时间点出现富集，这与发育时序相契合。与之相反，相较于神经发生，突触发生发生于发育后期，相关通路在E16.5与PND0这两个较晚时间点受到显著影响，涉及胆碱能、谷氨酸能及γ-氨基丁酸能（GABAergic）突触相关通路。本研究结合SLOS已知的生物学表型，探讨了这些转录组变化与富集通路的影响。