RAD51 knockout in murine liver (11-week)

RAD51 is a highly conserved DNA repair protein and is indispensable for the execution of homologous recombination, thereby participating in maintaining genomic stability. Since constitutive Rad51 knockout mice exhibit embryonic lethality, the physiological functions of RAD51, and the consequences of lacking it, are largely unknown. We herein demonstrated a critical role of RAD51 in postnatal liver development and regeneration. RAD51 is highly expressed during liver development and during regeneration following hepatectomy and hepatic injury, and is also elevated in liver-related diseases. We generated hepatocyte-specific Rad51 deletion mouse model (Rad51-CKO) to evaluate the function of RAD51 in liver development and regeneration.RAD51 deletion in postnatal hepatocytes results in aborted mitosis, global polyploidization, oxidative stress and cellular senescence. Remarkable liver fibrosis occurs as early as in 3-month-old Rad51fl/fl; Alb-Cre+/+ mice.The senescence-associated secretory phenotype in the livers of Rad51-CKO mice creates a niche that favors the activation and propagation of hepatic progenitor cells (HPCs) in which Rad51 is spared due to lack of Alb-Cre expression. The Rad51 functional HPCs and immature hepatocytes can thus proliferate vigorously, acquire increased malignancy, and eventually give rise to HCC. Our results thus demonstrate a novel function of RAD51 in liver development, homeostasis and tumorigenesis. The RAD51-CKO mice represent a unique genetic model for premature liver senescence, fibrosis, impaired regeneration and hepatocellular carcinogenesis. Liver tissue samples taken from three independent hepatocyte-specific Rad51 deletion mice and three wild-type littermate controls (11-week-old) were used for RNA-Seq.RAD51是一种高度保守的DNA修复蛋白（RAD51），在同源重组过程中不可或缺，进而参与维持基因组稳定性。由于组成型Rad51敲除小鼠会出现胚胎致死表型，目前对于RAD51的生理功能及其缺失所带来的影响仍知之甚少。本研究证实了RAD51在出生后肝脏发育与再生过程中的关键作用。RAD51在肝脏发育阶段、肝切除术及肝损伤后的再生过程中均呈高表达，且在多种肝脏相关疾病中表达上调。我们构建了肝细胞特异性Rad51敲除小鼠模型（Rad51-CKO），以评估RAD51在肝脏发育与再生中的功能。出生后肝细胞中RAD51的缺失会引发有丝分裂停滞、全基因组多倍体化、氧化应激以及细胞衰老。早在3月龄的Rad51fl/fl; Alb-Cre+/+小鼠中即可观察到显著的肝纤维化。Rad51-CKO小鼠肝脏中的衰老相关分泌表型会构建出一个适宜的微环境，促进肝祖细胞（HPCs）的激活与增殖；由于Alb-Cre不在肝祖细胞中表达，因此这些细胞内的RAD51并未被敲除。这些保留有RAD51功能的肝祖细胞与未成熟肝细胞可剧烈增殖，获得更高的恶性表型，并最终发展为肝细胞癌（HCC）。综上，本研究揭示了RAD51在肝脏发育、稳态维持以及肿瘤发生中的全新功能。Rad51-CKO小鼠可作为研究肝脏过早衰老、纤维化、再生受损以及肝细胞癌变的独特遗传模型。本研究选取3只独立构建的肝细胞特异性Rad51敲除小鼠，以及3只11周龄的野生型同窝对照小鼠的肝脏组织样本进行RNA测序（RNA-Seq）。