Hämmerle B, Vera-Samper E, Speicher S, Arencibia R, Martínez S, Tejedor F J
Instituto de Neurociencias, CSIC and Universidad Miguel Hernandez, San Juan, 03550 Alicante, Spain.
Dev Biol. 2002 Jun 15;246(2):259-73. doi: 10.1006/dbio.2002.0675.
The Minibrain (Mnb) gene encodes a new family of protein kinases that is evolutionarily conserved from insects to humans. In Drosophila, Mnb is involved in postembryonic neurogenesis. In humans, MNB has been mapped within the Down's Syndrome (DS) critical region of chromosome 21 and is overexpressed in DS embryonic brain. In order to study a possible role of Mnb on the neurogenesis of vertebrate brain, we have cloned the chick Mnb orthologue and studied the spatiotemporal expression of Mnb in proliferative regions of the nervous system. In early embryos, Mnb is expressed before the onset of neurogenesis in the three general locations where neuronal precursors are originated: neuroepithelia of the neural tube, neural crest, and cranial placodes. Mnb is transiently expressed during a single cell cycle of neuroepithelial progenitor (NEP) cells. Mnb expression precedes and widely overlaps with the expression of Tis21, an antiproliferative gene that has been reported to be expressed in the onset of neurogenic divisions of NEP cells. Mnb transcription begins in mitosis, continues during G(1), and stops before S-phase. Very interestingly, we have found that Mnb mRNA is asymmetrically localized during the mitosis of these cells and inherited by one of the sibling cells after division. We propose that Mnb defines a transition step between proliferating and neurogenic divisions of NEP cells.
微型脑（Mnb）基因编码一类新的蛋白激酶家族，该家族在从昆虫到人类的进化过程中保持保守。在果蝇中，Mnb参与胚胎后期神经发生。在人类中，MNB已被定位在21号染色体的唐氏综合征（DS）关键区域内，并且在DS胚胎脑中过度表达。为了研究Mnb在脊椎动物脑神经元生成中可能发挥的作用，我们克隆了鸡的Mnb同源物，并研究了Mnb在神经系统增殖区域的时空表达。在早期胚胎中，Mnb在神经发生开始之前就在神经元前体起源的三个一般位置表达：神经管的神经上皮、神经嵴和颅基板。Mnb在神经上皮祖细胞（NEP）的单个细胞周期中短暂表达。Mnb的表达先于Tis21的表达，且二者广泛重叠，Tis21是一种抗增殖基因，据报道在NEP细胞神经源性分裂开始时表达。Mnb转录在有丝分裂时开始，在G(1)期持续，在S期之前停止。非常有趣的是，我们发现Mnb mRNA在这些细胞的有丝分裂期间不对称定位，并在分裂后由其中一个姐妹细胞继承。我们提出Mnb定义了NEP细胞增殖性分裂和神经源性分裂之间的一个过渡步骤。
