Department of Biochemistry, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
Brain Res. 2011 Oct 28;1420:8-18. doi: 10.1016/j.brainres.2011.08.066. Epub 2011 Sep 2.
Tubulin, the subunit protein of microtubules, is an α/β heterodimer. Both α- and β-tubulin exist as numerous isotypes, differing in their amino acid sequences and encoded by different genes. The differences are highly conserved in evolution, suggesting that they are functionally significant. Neurons are a potentially very useful system for elucidating this significance, because they are highly differentiated cells and rich in tubulin isotypes. We have examined the distribution of β-tubulin isotypes in mouse primary cultured cortical neurons from embryonic fetus, newborn pups and adults. Neurons from both embryonic and adult mouse brains express the βI, βII, and βIII isotypes, but apparently not βIV or βV. βI, βII, and βIII are found in both cell bodies and neurites. However, the situation is different in newborn mice. Although βI and βIII are present in these neurons in both cell bodies and neurites and βIV is absent, just like in embryonic and adult mice, two striking differences were noted in the neurons from newborn mice. First, βV is apparently present evanescently in the neurons in both cell bodies and neurites. Interestingly, the βV was expressed strongly in newborn neurons after one day of culture; expression became much weaker after 3days, and almost disappeared after 5days. Second, the distribution of βII is different from other isotypes. After newborn mouse neurons were cultured for 3days, βII started to disappear partly from the cell bodies; this was much more pronounced after five days in culture. Our findings suggest that βII's major function may involve the neurites and not the cell body. They also raise the possibility that βV has a unique role in the neurons of newborn mice.
微管的亚基蛋白微管蛋白是一种 α/β 异二聚体。α-和 β-微管蛋白都存在许多同工型，在氨基酸序列上存在差异，并由不同的基因编码。这些差异在进化中高度保守，表明它们在功能上是重要的。神经元是阐明这一意义的一个非常有用的系统，因为它们是高度分化的细胞，富含微管蛋白同工型。我们研究了来自胚胎期胎儿、新生幼鼠和成年小鼠的原代皮质神经元中 β-微管蛋白同工型的分布。来自胚胎和成年小鼠大脑的神经元表达 βI、βII 和 βIII 同工型，但显然不表达 βIV 或 βV。βI、βII 和 βIII 存在于细胞体和轴突中。然而，新生小鼠的情况有所不同。尽管 βI 和 βIII 存在于这些神经元的细胞体和轴突中，而 βIV 不存在，就像在胚胎和成年小鼠中一样，在新生小鼠的神经元中还注意到了两个显著的差异。首先，βV 显然在细胞体和轴突中的神经元中短暂存在。有趣的是，βV 在新生神经元培养一天后表达强烈；培养 3 天后表达明显减弱，培养 5 天后几乎消失。其次，βII 的分布与其他同工型不同。在新生小鼠神经元培养 3 天后，βII 开始从细胞体部分消失；培养 5 天后更为明显。我们的研究结果表明，βII 的主要功能可能涉及轴突，而不是细胞体。它们还提出了βV 在新生小鼠神经元中可能具有独特作用的可能性。
