Naser Iftekhar Bin, Su Yuhong, Islam Shahidul M, Shinmyo Yohei, Zhang Sanbing, Ahmed Giasuddin, Chen Sandy, Tanaka Hideaki
Division of Developmental Neurobiology, Graduate School of Medical Sciences, Kumamoto University, Honjo, Kumamoto, Japan.
Dev Biol. 2009 Aug 15;332(2):351-9. doi: 10.1016/j.ydbio.2009.06.004. Epub 2009 Jun 6.
The mesencephalic V neurons and tectobulbar axons in chick embryo project over long distances that appear during the early development of the chick optic tectum. The mesencephalic V neuron and tectobulbar axonal growth begin at Hamburger and Hamilton stage 14 and stage 18, respectively. Both fibers proceed downward from the dorsal to the ventral side of the lateral wall of the optic tectum and then turn caudally and join the medial longitudinal fasciculus. Their axons appear in the most superficial layer of the tectum at early stages and do not cross the dorsal midline of the tectum. Here, we report the role of draxin, a recently identified axon guidance protein, in the formation of the ventrally directed tectum axonal tracts in chicken embryo. draxin is expressed in a high dorsal to low ventral gradient in chick optic tectum. In vitro experiments show that draxin repels neurite outgrowth from dorsal tectum explants. In vivo overexpression resulted in inhibition or misrouting of axon growth in the tectum. Therefore, draxin may be an important member of the collection of repulsive guidance molecules that regulate the formation of the ventrally directed tectum axon tracts.
鸡胚中的中脑V神经元和顶盖延髓轴突在鸡视顶盖早期发育过程中进行远距离投射。中脑V神经元和顶盖延髓轴突的生长分别始于哈伯格和汉密尔顿第14期和第18期。这两种纤维都从视顶盖侧壁的背侧向下延伸至腹侧，然后转向尾侧并加入内侧纵束。它们的轴突在早期出现在顶盖的最表层，且不穿过顶盖的背中线。在此，我们报告了最近鉴定出的轴突导向蛋白draxin在鸡胚腹侧顶盖轴突束形成中的作用。draxin在鸡视顶盖中以从高背侧到低腹侧的梯度表达。体外实验表明，draxin可排斥背侧顶盖外植体的神经突生长。体内过表达导致顶盖轴突生长受到抑制或发生错路。因此，draxin可能是调节腹侧顶盖轴突束形成的排斥性导向分子集合中的一个重要成员。
