Genetic Background-Dependent Role of Egr1 for Eyelid Development

EGR1 is an early growth response zinc finger transcription factor with broad actions, including in differentiation, mitogenesis, tumor suppression, and neuronal plasticity. Here we demonstrate that Egr1-/- C57BL/6-background mice have normal eyelid development, but back-crossing to BALB/c background for 4-5 generations resulted in defective eyelid development by embryonic day E15.5, at which time EGR1 was expressed in eyelids of WT mice. Defective eyelid formation correlated with profound ocular anomalies evident by post-natal days 1-4, including severe cryptophthalmos, microphthalmia or anophthalmia, retinal dysplasia, keratitis, corneal neovascularization, cataracts, and calcification. The BALB/c albino phenotype-associated Tyrc tyrosinase mutation appeared to contribute to the phenotype, as crossing the independent Tyrc-2J allele to Egr1-/- C57BL/6 mice also produced ocular abnormalities, albeit less severe than those in Egr1-/- BALB/c mice. Thus, EGR1 in a genetic background-dependent manner plays a critical role in mammalian eyelid development and closure, with subsequent impact on ocular integrity. RNA-Seq analyses using total RNA from eyes of newborn and adult Egr1-/- BALB/c mice, and total RNA from each eye of three 3-day old Egr1-/- mice with unmerged eyelids as well as Egr1+/- littermate controls早期生长应答锌指转录因子（EGR1）具备广泛生物学功能，涉及细胞分化、有丝分裂发生、肿瘤抑制及神经可塑性等过程。本研究证实，Egr1纯合敲除（Egr1-/-）的C57BL/6背景小鼠眼睑发育正常，但将其回交至BALB/c背景达4-5代后，胚胎发育至第15.5天（E15.5）时即可观察到眼睑发育缺陷；此时野生型（WT）小鼠的眼睑中可检测到EGR1的表达。眼睑发育缺陷与出生后1-4天即可观测到的严重眼部异常密切相关，包括重度隐眼症、小眼球症或无眼球症、视网膜发育不良、角膜炎、角膜新生血管形成、白内障及钙化等。与BALB/c白化表型相关的酪氨酸酶Tyrc突变似乎参与了该异常表型的形成：将独立的Tyrc-2J等位基因导入Egr1纯合敲除的C57BL/6背景小鼠后，同样可引发眼部异常，尽管其严重程度弱于Egr1纯合敲除的BALB/c背景小鼠。综上，EGR1以遗传背景依赖的方式在哺乳动物眼睑发育与闭合过程中发挥关键作用，并进一步影响眼部结构完整性。本研究采用RNA测序（RNA-Seq）技术，以新生及成年Egr1纯合敲除的BALB/c背景小鼠眼部总RNA、3只出生3天且眼睑未闭合的Egr1纯合敲除小鼠的单眼总RNA，及其Egr1杂合（Egr1+/-）同窝对照小鼠的眼部总RNA为样本开展分析。