Kamma H, Portman D S, Dreyfuss G
Institute of Basic Medical Sciences, University of Tsukuba, Ibaraki, Japan.
Exp Cell Res. 1995 Nov;221(1):187-96. doi: 10.1006/excr.1995.1366.
HnRNP proteins are abundant nucleoplasmic pre-mRNA-binding proteins which have important roles in the biogenesis of mRNA. Although hnRNP proteins have been extensively characterized in cultured cell lines, little is known about their expression in animal tissues. Here, we have undertaken a systematic survey of the expression of major hnRNP proteins in mouse tissue using specific monoclonal antibodies. Immunohistochemical staining demonstrated that hnRNP proteins C, L, and U were localized to nuclei in all tissues examined. However, cytoplasmic expression of hnRNP A1, D, F/H, and K was also detected in several tissues, suggesting that these proteins have roles in the cytoplasm as well as the nucleus. Importantly, the relative amounts of different hnRNP proteins varied among cell types. This was especially striking in neuronal and reproductive cells. In the brain, certain neuronal cell types contained more hnRNP proteins than glial cells, perhaps reflecting increased levels of neuronal transcription and RNA processing. In the ovary, oocytes contained exceptionally high concentrations of hnRNP proteins as compared to follicular and stromal cells. In the testis, the expression of hnRNP proteins was generally high and was found to be tightly regulated during spermatogenesis. Specifically, hnRNP A1 was highly expressed only in early spermatogonia and absent in later stages. These findings demonstrate that hnRNP proteins do not exist in a fixed stoichiometry across different cell types. Furthermore, as the relative amounts of pre-mRNA-binding proteins (e.g., A1 and ASF/SF2) can affect alternative splicing patterns, the variations that we have observed could profoundly affect cell-specific gene expression.
不均一核糖核蛋白（HnRNP）是丰富的核质前体mRNA结合蛋白，在mRNA生物合成中发挥重要作用。尽管HnRNP蛋白已在培养细胞系中得到广泛表征，但对其在动物组织中的表达了解甚少。在此，我们使用特异性单克隆抗体对小鼠组织中主要HnRNP蛋白的表达进行了系统研究。免疫组织化学染色表明，HnRNP蛋白C、L和U定位于所有检测组织的细胞核中。然而，在几种组织中也检测到了HnRNP A1、D、F/H和K的细胞质表达，这表明这些蛋白在细胞质和细胞核中均发挥作用。重要的是，不同HnRNP蛋白的相对含量在不同细胞类型中有所不同。这在神经元细胞和生殖细胞中尤为明显。在大脑中，某些神经元细胞类型所含的HnRNP蛋白比神经胶质细胞更多，这可能反映了神经元转录和RNA加工水平的提高。在卵巢中，与卵泡细胞和基质细胞相比，卵母细胞中HnRNP蛋白的浓度异常高。在睾丸中，HnRNP蛋白的表达普遍较高，且在精子发生过程中受到严格调控。具体而言，HnRNP A1仅在早期精原细胞中高表达，在后期阶段则不存在。这些发现表明，HnRNP蛋白在不同细胞类型中并非以固定的化学计量存在。此外，由于前体mRNA结合蛋白（如A1和ASF/SF2）的相对含量会影响可变剪接模式，我们观察到的这些变化可能会深刻影响细胞特异性基因表达。
