《国际发育生物学杂志》10月刊以封面文章发表了中科院水生所关于“银鲫cagMdkb基因在胚胎发育过程中发育表达”的研究成果(The International Journal of Developmental Biology, 2007, 51: 761-769)。该论文是在桂建芳研究员指导下由博士研究生尹隽等人共同完成。封面图片显示的是过量注射野生型CagMdkb RNAs 造成的银鲫胚胎前脑组组织和眼睛发育受到抑制等严重缺陷。
Mdk是一种分泌型蛋白，在神经发育中有重要作用，并参与人类肿瘤的形成。但是，在不同种类的脊椎动物中，Mdk基因的表达模式却大相径庭。该文报道了从银鲫10体节胚胎的SMART cDNA文库中克隆的银鲫Mdkb基因的特征、表达图式及功能。在银鲫胚胎发育过程中，CagMdkb基因在原肠期开始表达，在10体节期时表达量上升到最高，此后表达量保持稳定。Western印迹显示胚胎早期有一条19kDa的母源CagMdkb蛋白带，合子CagMdkb蛋白从原肠期开始产生。大约在10体节时，19kDa的CagMdkb蛋白剪掉了信号肽，变成17kDa的成熟蛋白。在胚胎发育早期，母源的CagMdkb蛋白在所有卵裂球的细胞质中被检测到。当胚胎发育到18体节期时，新合成蛋白的信号出现在后脑的一对巨大神经元中。此后，新合成的CagMdkb蛋白延伸到前脑、中脑、后脑的神经元和脊髓的神经纤维中。3A10抗体共定位表明这对巨大的神经元是Mauthner神经元。在银鲫和斑马鱼受精卵中进行的基因转移实验发现，野生型CagMdkb RNAs的过量表达造成了胚胎前脑组织和眼睛发育受到抑制等严重缺陷，并发现其功能的发挥还依赖于它的分泌特性。上述结果表明，CagMdkb在鱼类神经系统的早期发育中起着重要作用。
该研究是在国家973计划项目和国家自然科学基金项目的支持下完成的。（水生生物研究所）
原始出处:
Int. J. Dev. Biol. 51: 761 - 769 (2007)
doi: 10.1387/ijdb.072346jy
Developmental expression of CagMdkb during gibel carp embryogenesis
Jun Yin, Jian-Hong Xia, Xin-Zheng Du, Jun Liu, Li Zhou, Yun-Han Hong and Jian-Fang Gui*
State Key Laboratory of Freshwater Ecology and Biotechnology, Wuhan Center for Developmental Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Graduate School of the Chinese Academy of Sciences, Wuhan, China
ABSTRACT Midkine (Mdk) genes have been revealed to have different expression patterns in vertebrates and therefore, additional studies on Mdk expression patterns are required in more species. In this study, CagMdkb has been cloned and characterized from a SMART cDNA library of 10-somite stage embryos of Carassius auratus gibelio. Its full length cDNA is 1091 bp and encodes a sequence of 147 amino acids, which shows 97.3% identity to zebrafish Mdkb on the amino acid level. RT-PCR analysis reveals that CagMdkb is first transcribed in gastrula embryos and maintains a relatively stable expression level during subsequent embryogenesis. Western blot analysis reveals a 19 kDa maternal CagMdkb protein band and the zygotic CagMdkb protein is expressed from gastrula stage. At around 10 somite stage, the 19 kDa CagMdkb is processed to another protein band of about 17 kDa, which might be the secreted form with the 21-residue signal peptide removed. With immunofluorescence analysis, maternal CagMdkb protein was found to be localized in each blastamere cell of early embryos. The zygotic CagMdkb positive fluorescence signal was detected from a pair of large neurons at 18-somite stage. At the later stages, CagMdkb protein was also extended to numerous small neurons in the forebrain, midbrain and hindbrain, as well as to nerve fibers in the spinal cord. Co-localization with 3A10 antibody revealed CagMdkb immunoreactivity on developing Mauthner neurons, a member of reticulospinal neurons. In addition, ectopic expression of CagMdkb in early embryos of gibel carp and zebrafish suppressed head formation and CagMdkb function was found to depend on secretory activity. All these findings indicate that CagMdkb plays an important role in neural development during gibel carp embryogenesis and there is functional conservation of Mdkb in fish head formation.
Key words: Mdkb, embryogenesis, Mauthner cell, nerve development, gibel carp
*Corresponding author e-mail: jfgui@ihb.ac.cn
