General consensus states that immunoglobulins are exclusively expressed by B lymphocytes to form the first line of defense against common pathogens. Here, we provide compelling evidence for the expression of two heavy chain immunoglobulin genes in subpopulations of neurons in the mouse brain and spinal cord. RNA isolated from excitatory and inhibitory neurons through ribosome affinity purification revealed Ighg3 and Ighm transcripts encoding for the constant (Fc), but not the variable regions of IgG3 and IgM. Because, in the absence of the variable immunoglobulin regions, these transcripts lack the canonical transcription initiation site used in lymphocytes, we screened for alternative 5' transcription start sites and identified a novel 5' exon adjacent to a proposed promoter element. Immunohistochemical, Western blot, and in silico analyses strongly support that these neuronal transcripts are translated into proteins containing four Immunoglobulin domains. Our data thus demonstrate the expression of two Fc-encoding genes Ighg3 and Ighm in spinal and supraspinal neurons of the murine CNS and suggest a hitherto unknown function of the encoded proteins.

中文翻译：

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免疫球蛋白恒定域基因在小鼠中枢神经系统神经元中的表达。

普遍共识指出，免疫球蛋白仅由 B 淋巴细胞表达，形成抵御常见病原体的第一道防线。在这里，我们为小鼠大脑和脊髓神经元亚群中两个重链免疫球蛋白基因的表达提供了令人信服的证据。通过核糖体亲和纯化从兴奋性和抑制性神经元中分离的 RNA 揭示了Ighg3和Ighm转录物编码恒定区 (Fc)，但不编码 IgG3 和 IgM 的可变区。因为，在没有可变免疫球蛋白区域的情况下，这些转录物缺乏淋巴细胞中使用的规范转录起始位点，我们筛选了替代的 5' 转录起始位点，并确定了与提议的启动子元件相邻的新的 5' 外显子。免疫组织化学、蛋白质印迹和计算机分析强烈支持这些神经元转录物被翻译成含有四个免疫球蛋白结构域的蛋白质。因此，我们的数据证明了两个 Fc 编码基因Ighg3和Ighm在鼠 CNS 的脊髓和脊髓上神经元中的表达，并表明编码蛋白质的功能迄今未知。