Schreiber J, Enderich J, Sock E, Schmidt C, Richter-Landsberg C, Wegner M
Zentrum für Molekulare Neurobiologie, Universität Hamburg, Martinistrasse 52, D-20246 Hamburg, Germany.
J Biol Chem. 1997 Dec 19;272(51):32286-93. doi: 10.1074/jbc.272.51.32286.
Class III POU proteins are prominent regulators of neural development. Tst-1/Oct6/SCIP, for instance, is essential for terminal differentiation of myelinating Schwann cells in the peripheral nervous system. Although Tst-1/Oct6/SCIP is also expressed in the myelin forming oligodendrocytes of the central nervous system, targeted deletion of Tst-1/Oct6/SCIP failed to reveal a gross alteration of myelination in the central nervous system. To better understand this apparent discrepancy, we examined the expression of POU proteins in both cultured primary oligodendrocytes and in the oligodendrocyte-like CG-4 cell line. These cells expressed Tst-1/Oct6/SCIP, Brn-1, and Brn-2 in significant amounts, indicating that Brn-1 and Brn-2 might have the capacity to compensate loss of Tst-1/Oct6/SCIP. We show that Tst-1/Oct6/SCIP, Brn-1, and Brn-2 were all down-regulated during the early phases of oligodendrocyte development both on RNA and protein level. All three POU proteins exhibited similar DNA binding characteristics. When promoters consisting of a single POU protein-binding site adjacent to a TATA box were used as reporters in transient transfections, Brn-1 proved to be a weaker transcriptional activator than Tst-1/Oct6/SCIP. In agreement with this, we found the transactivation domain of Brn-1, which we mapped between amino acids 119 and 237, significantly weaker than the transactivation domain of Tst-1/Oct6/SCIP. Taken together, our data imply a partial, but not complete redundancy between POU proteins in oligodendrocytes.
III类POU蛋白是神经发育的重要调节因子。例如,Tst-1/Oct6/SCIP对于外周神经系统中形成髓鞘的施万细胞的终末分化至关重要。尽管Tst-1/Oct6/SCIP也在中枢神经系统形成髓鞘的少突胶质细胞中表达,但靶向缺失Tst-1/Oct6/SCIP并未揭示中枢神经系统髓鞘形成的明显改变。为了更好地理解这一明显差异,我们检测了原代培养的少突胶质细胞和少突胶质细胞样CG-4细胞系中POU蛋白的表达。这些细胞大量表达Tst-1/Oct6/SCIP、Brn-1和Brn-2,表明Brn-1和Brn-2可能有能力补偿Tst-1/Oct6/SCIP的缺失。我们发现,在少突胶质细胞发育的早期阶段,Tst-1/Oct6/SCIP、Brn-1和Brn-2在RNA和蛋白质水平均下调。所有三种POU蛋白都表现出相似的DNA结合特性。当由与TATA框相邻的单个POU蛋白结合位点组成的启动子用作瞬时转染的报告子时,Brn-1被证明是比Tst-1/Oct6/SCIP弱的转录激活因子。与此一致的是,我们发现Brn-1的反式激活结构域(我们将其定位在氨基酸119和237之间)明显弱于Tst-1/Oct6/SCIP的反式激活结构域。综上所述,我们的数据表明少突胶质细胞中POU蛋白之间存在部分但非完全的冗余。