Analysis of ERK2 roles in immunoregulation by ERK2 mutant mice

丝裂原活化蛋白激酶（MAPK）响应于各种细胞外刺激而被活化。细胞外信号调节激酶（ERK）是MAPK家族的一员，参与T细胞的分化、增殖和细胞因子的产生。ERK家族由ERK 1和ERK 2两个成员组成。最近，在ERK 1缺陷小鼠中报告了胸腺细胞成熟缺陷。然而，ERK 2在免疫系统调节中的作用仍有待确定。在这里，我们表明，有针对性地破坏小鼠ERK 2基因的结果在胚胎死亡的E11.5和严重异常的胎盘。在这些动物中，胎盘的胎盘层非常薄，很少观察到胎儿血管。ERK 2突变体可以通过ERK 2的转基因表达来挽救，这表明这些异常是由ERK 2缺陷引起的。虽然ERK 2缺陷的胎儿比野生型同窝仔小得多，但这似乎是继发于胎盘功能障碍。当胎盘缺陷被四倍体聚集挽救时，ERK 2缺陷的胎儿生长与同窝对照一样。因此，我们建立了ERK 2条件性基因敲除小鼠，以研究ERK 2在免疫系统中的生理作用。我们使用LCK-Cre转基因小鼠产生T细胞特异性ERK 2缺陷小鼠。这些小鼠存活，超过95%的ERK 2基因在胸腺细胞中被破坏。ERK 2蛋白在胸腺细胞中未检测到。在胸腺中，CD 3 ^<high>CD 4 ^+或CD 8 ^+成熟T细胞显著减少。因此，ERK 2对T细胞的发育至关重要。

Mitogen-activated protein kinases(MAPKs) are activated in response to various extracellular stimuli. Extracellular signal-regulated kinase(ERK), a MAPK family, has been implicated in T cell differentiation, proliferation and cytokine production. The ERK family consists of two members, ERK1 and ERK2. Recently, defective thymocyte maturation has been reported in ERK1-deficient mice. However, roles of ERK2 in the regulation of immune system remain to be determined. Here we show that the targeted disruption of the mouse ERK2 gene results in embryonic lethality by E11.5 and severe abnormality of the placenta. In these animals, the labyrinthine layer of the placenta is very thin and few fetal blood vessels are observed. ERK2 mutants can be rescued by the transgenic expression of ERK2, demonstrating that these abnormalities are caused by ERK2-deficiency. Although ERK2-deficient fetuses are much smaller than wild-type littermates, this seems to be secondary to malfunction of the placenta. When the placental defect is rescued by tetraploid-aggregation, ERK2-deficient fetuses grow as well as littermate controls.As described above, ERK2-deficient mice were embryonic lethal due to placental defect. So we generated ERK2 conditional knockout mice to study the physiological role of ERK2 in the immune system. We generated T cell-specific ERK2-deficient mice using LCK-Cre transgenic mice. These mice were viable and more than 95% ERK2 gene was disrupted in the thymocytes. ERK2 protein was undetectable in the thymocytes. In the thymus, CD3^<high> CD4^+ or CD8^+ mature T cells were significantly decreased. Thus, ERK2 is essential for development of T cells.