Barbarese E, Pfeiffer S E
Proc Natl Acad Sci U S A. 1981 Mar;78(3):1953-7. doi: 10.1073/pnas.78.3.1953.
The expression of myelin basic protein, a major component of the myelin membrane, was studied in the absence of myelin formation in a unique situation in which these two processes have been uncoupled. The oligodendrocytes that contained myelin basic protein were identified by immunofluorescence in primary dispersed cultures derived from 20-day-old fetal rat brain. Their number increased 20-fold between 15 and 34 days in culture. Morphologically identifiable myelin was never observed. The oligodendrocytes elaborated a complex network of processes and membranous sheets resembling "unfurled" myelin. Myelin basic protein appeared concomitantly in the perikaryon, processes, and membranous sheets of the oligodendrocytes and remained distributed in these compartments throughout the culture period. The oligodendrocytes synthesized the four forms of myelin basic protein found in rodent brain with molecular weights of 21,500, 18,500, 17,000, and 14,000 and modulated their expression with time in culture. The onset of rapid myelin basic protein accumulation, as measured by radioimmunoassay, took place after 25 days in culture. Myelin basic protein accumulated at the rate of 0.2 fmol per oligodendrocyte per day and reached a level of 300 pmol/mg of protein by 34 days. By 60 days, the amount of myelin basic protein had declined to 100 pmol/mg of protein, a level maintained up until at least 120 days. When the amount of myelin basic protein was correlated with the number of oligodendrocytes, it was estimated that each induced cell contained on average 1 fmol of this protein at the three time points (15, 28, and 34 days in culture) at which cells were counted. Our results indicate that the accumulation, modulation of the molecular forms, and insertion of myelin basic protein into the membrane can occur in the absence of myelin formation, but that continued metabolic stability, subcellular sequestration, and fine control of the relative proportions of the different forms of myelin basic protein may be dependent on myelin morphogenesis.
髓鞘碱性蛋白是髓鞘膜的主要成分，在一种独特的情况下，即这两个过程已解偶联，髓鞘形成缺失时，对其表达进行了研究。在源自20日龄胎鼠脑的原代分散培养物中，通过免疫荧光鉴定出含有髓鞘碱性蛋白的少突胶质细胞。在培养的15至34天之间，它们的数量增加了20倍。从未观察到形态上可识别的髓鞘。少突胶质细胞形成了一个复杂的过程网络和类似于“展开”的髓鞘的膜片。髓鞘碱性蛋白同时出现在少突胶质细胞的胞体、过程和膜片中，并在整个培养期间一直分布在这些隔室中。少突胶质细胞合成了在啮齿动物脑中发现的四种形式的髓鞘碱性蛋白，分子量分别为21,500、18,500、17,000和14,000，并在培养过程中随时间调节其表达。通过放射免疫测定法测量，髓鞘碱性蛋白快速积累的起始发生在培养25天后。髓鞘碱性蛋白以每天每个少突胶质细胞0.2 fmol的速率积累，到34天时达到300 pmol/mg蛋白质的水平。到60天时，髓鞘碱性蛋白的量已降至100 pmol/mg蛋白质，这一水平至少维持到120天。当髓鞘碱性蛋白的量与少突胶质细胞的数量相关联时，据估计，在计数细胞的三个时间点（培养15、28和34天），每个诱导细胞平均含有1 fmol这种蛋白质。我们的结果表明，髓鞘碱性蛋白的积累、分子形式的调节以及插入膜中可以在髓鞘形成缺失的情况下发生，但不同形式的髓鞘碱性蛋白的持续代谢稳定性、亚细胞隔离以及相对比例的精细控制可能依赖于髓鞘形态发生。
