Albi E, Viola-Magni M P
Department of Biochemical Sciences and Molecular Biotechnology, Physiopathology, Policlinico Monteluce, Perugia, Italy.
Cell Biochem Funct. 2003 Sep;21(3):211-5. doi: 10.1002/cbf.1075.
After the first histochemical demonstration by Chayen and Gahan of the presence of phospholipids and especially of sphingomyelin in chromatin, this became the object of long debate and of contradictory results. The general conclusion was that the presence of phospholipids may due to contamination during the isolation of chromatin. More recently the existence of a phospholipid chromatin fraction was confirmed by demonstrating that isolated hepatocyte nuclei, labelled by saturated and unsaturated radioiodination method, showed the presence of radioactivity only in the membrane and not in the isolated chromatin. The phospholipid composition showed an enrichment in sphingomyelin which increased during hepatocyte maturation or erythroleukemic cell differentiation induced by DMSO. A decrease in sphingomyelin was observed at the beginning of the S-phase in regenerating liver or in cultured proliferating cells. These changes were due to the presence of sphingomyelinase and sphingomyelin synthase in the chromatin, the activity of which paralleled the variation in sphingomyelin content. The sphingomyelin was co-localized with RNA as shown by biochemical and electron microscopy methods. Using bromo-uridine it was demonstrated that labelled RNA and sphingomyelin were present in actively transcribing nuclear regions. Isolated nuclear complexes after DNase and RNase digestion contained not only protein, but also RNA and sphingomyelin. After hydrolysis of sphingomyelin the RNAse-resistant RNA becomes RNAse sensitive. It can therefore be concluded that sphingomyelin and the related enzymes are present in the chromatin; sphingomyelin may have a role in RNA transcription protecting RNA by RNAse digestion before its transfer to the cytoplasm.
在查延和加汉首次通过组织化学方法证明染色质中存在磷脂尤其是鞘磷脂之后，这一发现成为了长期争论的对象，且结果相互矛盾。普遍的结论是，磷脂的存在可能是染色质分离过程中受到污染所致。最近，通过证明用饱和及不饱和放射性碘化方法标记的分离肝细胞细胞核，放射性仅存在于膜中而非分离出的染色质中，从而证实了磷脂染色质组分的存在。磷脂组成显示鞘磷脂有所富集，在二甲基亚砜诱导的肝细胞成熟或红白血病细胞分化过程中其含量增加。在再生肝脏或培养的增殖细胞的S期开始时，观察到鞘磷脂含量下降。这些变化是由于染色质中存在鞘磷脂酶和鞘磷脂合酶，其活性与鞘磷脂含量的变化平行。通过生化和电子显微镜方法表明，鞘磷脂与RNA共定位。使用溴尿苷证明，标记的RNA和鞘磷脂存在于活跃转录的核区域。经DNA酶和RNA酶消化后的分离核复合物不仅含有蛋白质，还含有RNA和鞘磷脂。鞘磷脂水解后，抗RNA酶的RNA变得对RNA酶敏感。因此可以得出结论，染色质中存在鞘磷脂及相关酶；鞘磷脂可能在RNA转录中发挥作用，在RNA转移到细胞质之前通过抵抗RNA酶消化来保护RNA。
