Bhattacharya B, Sarkar P K
Department of Cell Biology, Indian Institute of Chemical Biology, Calcutta, India.
Int J Dev Neurosci. 1991;9(1):89-99. doi: 10.1016/0736-5748(91)90076-x.
Studies on tubulin gene expression in brains from three different species, viz rat, mouse and chick, varying with respect to their periods of synaptogenesis, show that the rise and fall in the level of tubulin during synaptogenesis is closely parallel to that of tubulin mRNA. In all three species, the onset of synaptogenesis is accompanied by a dramatic rise in the level of tubulin which continues till the midphase and then declines to adult level by the end of synaptogenesis. The chick alpha- and beta-tubulin coding region probes, pT1 and pT2, which have a 80-90% homology with rat/mouse sequences, were employed to determine the overall levels of alpha- and beta-tubulin mRNA in all samples. Quantitation of tubulin mRNA by dot hybridization revealed a closely parallel change in the levels of both alpha- and beta-tubulin mRNA. In analogy with that of tubulin, the mRNA levels in rat and mouse brain increased progressively from birth till postnatal day 5 and that in the chick brain increased from day 7 till day 11 of embryonic development. In all three cases, the peak levels of tubulin mRNA corresponded closely with the midphase of synaptogenesis and declined almost to adult levels by the end of synaptogenesis. The sudden decline in the level of tubulin as well as its mRNA during the middle of synaptogenesis suggests that the repression of tubulin gene expression is neither due to cessation of cell division nor cell differentiation. Instead, it is likely to be due to the autoregulatory property of tubulin which leads to rapid turnover of its own mRNA when a sufficient level of intracellular tubulin accumulates during the midphase of synaptogenesis.
对大鼠、小鼠和鸡这三种不同物种的大脑中微管蛋白基因表达的研究表明，在突触发生期，微管蛋白水平的上升和下降与微管蛋白mRNA的变化密切平行。这三种物种在突触发生开始时，微管蛋白水平急剧上升，持续到中期，然后在突触发生结束时降至成年水平。利用与大鼠/小鼠序列有80 - 90%同源性的鸡α-和β-微管蛋白编码区探针pT1和pT2，来测定所有样本中α-和β-微管蛋白mRNA的总体水平。通过点杂交对微管蛋白mRNA进行定量分析，结果显示α-和β-微管蛋白mRNA水平变化密切平行。与微管蛋白类似，大鼠和小鼠大脑中的mRNA水平从出生到出生后第5天逐渐增加，鸡大脑中的mRNA水平从胚胎发育第7天到第11天增加。在所有三种情况下，微管蛋白mRNA的峰值水平与突触发生的中期密切对应，并在突触发生结束时几乎降至成年水平。在突触发生中期微管蛋白及其mRNA水平的突然下降表明，微管蛋白基因表达的抑制既不是由于细胞分裂的停止，也不是由于细胞分化。相反，这可能是由于微管蛋白的自调节特性，当在突触发生中期细胞内微管蛋白积累到足够水平时，会导致其自身mRNA的快速周转。
