The Mest （mesoderm-specific transcript） gene has been considered an imprinting gene in human and mouse, and was also confirmed in other mammals and flowering plants. To investigate the function and evolution of this gene, the cDNA of full length Mest gene was obtained using 5＇- and 3＇-RACE from the Chinese Large Toad （Bufo gargarizans）. The transcript is 1 325bp in length which contains a complete open reading frame （ORF） encoding a polypeptide of 326 amino acids （GenBank accession number： ABQ10905）. There is a typical 0./13 hydrolase fold domain in the putative gene product, and it shows high similarity to sequence of homologous protein of Xenopus tropicali （86%）, mammlian （70% - 80%）. RT-PCR （reverse transcriptase-polymerase chain reaction） analysis demonstrated that the Bufo gargarizans Mest （BgMest） gene is expressed widely in testis, ovary, liver, kidney, spleen, brain, stomach and lung. The conservation of the BgMest gene sequences, protein secondary structure of the BgMest protein, in addition to the expression pattern of the BgMest gene, suggested that the function of BgMest was conserved in amphibians. However, the phylogenetic tree of the imprinting gene of the mammals and other vertebrates examined in this study indicated their divergent origins.
目的比较青年猫和老年猫上丘浅层(superricial Superior Colliculus,sSC)GABA能神经元及其表达的年龄相关性变化,探讨老年个体视觉功能衰退的相关神经机理。方法Nissl染色显示上丘浅层结构及神经元、免疫组织化学ABC法标记GABA免疫阳性神经元。光镜下观察,采集图像,并利用图像分析软件对带状层、浅灰质层和视层神经元及GABA免疫阳性神经元及其灰度值进行分析统计。结果GABA免疫阳性神经元、阳性纤维及其终末在青年猫及老年猫上丘浅层均有分布。与青年猫相比,老年猫上丘浅灰质层、视层神经元和GABA免疫阳性神经元密度及其GABA免疫阳性反应强度均显著下降(P<0.01)(免疫反应强度与平均灰度值成反比);带状层神经元密度也显著下降(P<0.01),但其GABA免疫阳性神经元密度无显著变化(P>0.05)。结论衰老过程中猫上丘浅层GABA能神经元的丢失和GABA表达的下降,可能是在上丘水平上导致老年个体视觉功能衰退的重要因素之一。
