Shimizu A, Honjo T
Center for Molecular Biology and Genetics, Kyoto University, Japan.
FASEB J. 1993 Jan;7(1):149-54. doi: 10.1096/fasebj.7.1.7916698.
We have detected an immunoglobulin heavy-chain trans-mRNA of the epsilon class in which the variable region of the human transgenic mu chain is correctly spliced to the first exon of the endogenous mouse epsilon constant region. Together with our previous observations, all the endogenous isotypes that are targets of class switching have proved to be expressed as trans-mRNA. This indicates that immunoglobulin trans-mRNA synthesis is a general mechanism to express a second heavy-chain isotype with the variable region of the transgenic mu chain. Synthesis of epsilon trans-mRNA is regulated in a way similar to the trans-mRNAs of the gamma subclasses or class switching to epsilon, i.e., interleukin-4 can induce the germline transcript of the epsilon constant region, but costimulation with lipopolysaccharide is necessary for epsilon trans-mRNA expression. The amount of epsilon trans-mRNA induced is similar to that of gamma 1 and higher than expected as judged from the rate of class switching to epsilon. All these data are consistent with our previous hypothesis that trans-mRNA is synthesized by a trans-splicing mechanism and that this mechanism is involved in the simultaneous multiple-isotype expression of immunoglobulin in a single B lymphocyte.
我们检测到一种ε类免疫球蛋白重链反式mRNA，其中人类转基因μ链的可变区正确剪接到内源性小鼠ε恒定区的第一个外显子上。结合我们之前的观察结果，所有作为类别转换靶点的内源性同种型均被证明以反式mRNA的形式表达。这表明免疫球蛋白反式mRNA合成是一种利用转基因μ链可变区表达第二种重链同种型的普遍机制。ε反式mRNA的合成调控方式与γ亚类的反式mRNA或向ε的类别转换类似，即白细胞介素-4可诱导ε恒定区的胚系转录本，但ε反式mRNA表达需要脂多糖的共刺激。诱导产生的ε反式mRNA量与γ1的量相似，且从向ε的类别转换率判断高于预期。所有这些数据都与我们之前的假设一致，即反式mRNA是通过反式剪接机制合成的，且该机制参与单个B淋巴细胞中免疫球蛋白的同时多同种型表达。
