Analysis of ERK2 roles in immunoregulation by ERK2 mutant mice

丝裂原活化蛋白激酶(MAPKs)是细胞外刺激下的一种激活蛋白。细胞外信号调节激酶(ERK)是一个MAPK家族，参与T细胞的分化、增殖和细胞因子的产生。ERK家族由ERK1和ERK2两个成员组成。最近，有报道称ERK1基因缺陷小鼠胸腺细胞成熟有缺陷。然而，ERK2在免疫系统调节中的作用仍有待确定。在这里，我们表明，小鼠ERK2基因的靶向破坏导致E11.5导致胚胎死亡和胎盘严重异常。在这些动物中，胎盘的迷宫层非常薄，几乎没有观察到胎儿血管。ERK2的转基因表达可以挽救ERK2突变体，表明这些异常是由ERK2缺乏引起的。虽然ERK2基因缺陷的胎儿比野生型胎仔小得多，但这似乎是胎盘功能障碍的次要原因。当通过四倍体聚集挽救胎盘缺陷时，ERK2缺陷的胎儿生长和产仔对照一样。如上所述，ERK2缺陷小鼠因胎盘缺陷而胚胎死亡。因此，我们建立了ERK2条件性基因敲除小鼠来研究ERK2在免疫系统中的生理作用。我们用LCK-Cre转基因小鼠产生了T细胞特异性ERK2缺陷小鼠。这些小鼠是存活的，95%以上的ERK2基因在胸腺细胞中被破坏。胸腺细胞中未检测到ERK2蛋白。在胸腺中，CD3+、CD8+成熟T细胞明显减少。因此，ERK2对于T细胞的发育是必不可少的。

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.