Zinc finger structure-function in Ikaros

The zinc finger motif was used as a vehicle for the initial discovery of Ikaros in the context of T-cell differentiation and has been central to all subsequent analyses of Ikaros function. The Ikaros gene is alternately spliced to produce several isoforms that confer diversity of function and consequently have complicated analysis of the function of Ikaros in vivo. Key features of Ikaros in vivo function are associated with six C2H2 zinc fingers; four of which are alternately incorporated in the production of the various Ikaros isoforms. Although no complete structures are available for the Ikaros protein or any of its family members, considerable evidence has accumulated about the structure of zinc fingers and the role that this structure plays in the functions of the Ikaros family of proteins. This review summarizes the structural aspects of Ikaros zinc fingers, individually, and in tandem to provide a structural context for Ikaros function and to provide a structural basis to inform the design of future experiments with Ikaros and its family members.     

Members of the Ikaros gene family are present in early representative vertebrates

Members of the Ikaros multigene family of zinc finger proteins are expressed in a tissue-specific manner and most are critical determinants in the development of both the B and T lymphocytes as well as NK and dendritic APC lineages. A PCR amplification strategy that is based on regions of shared sequence identity in Ikaros multigene family members found in mammals and several other vertebrates has led to the recovery of cDNAs that represent the orthologues of Ikaros, Aiolos, Helios, and Eos in Raja eglanteria (clearnose skate), a cartilaginous fish that is representative of an early divergence event in the phylogenetic diversification of the vertebrates. The tissue-specific patterns of expression for at least two of the four Ikaros family members in skate resemble the patterns observed in mammals, i.e., in hematopoietic tissues. Prominent expression of Ikaros in skate also is found in the lymphoid Leydig organ and epigonal tissues, which are unique to cartilaginous fish. An Ikaros-related gene has been identified in Petromyzon marinus (sea lamprey), a jawless vertebrate species, in which neither Ig nor TCRs have been identified. In addition to establishing a high degree of evolutionary conservation of the Ikaros multigene family from cartilaginous fish through mammals, these studies define a possible link between factors that regulate the differentiation of immune-type cells in the jawed vertebrates and related factors of unknown function in jawless vertebrates.     

尼罗罗非鱼Ikaros基因的克隆及表达分析

为揭示尼罗罗非鱼Ikaros基因结构特征及其在抗病原感染中的免疫调控机制, 实验采用RT-PCR和RACE方法克隆了尼罗罗非鱼Ikaros的cDNA序列以及利用PCR和染色体步移技术克隆了Ikaros的基因组DNA序列, 通过荧光定量PCR分析了Ikaros mRNA的组织分布及其对无乳链球菌感染的响应。结果表明, 克隆的尼罗罗非鱼Ikaros基因组DNA为20454 bp, 包括7个内含子和8个外显子, 经可变剪接可形成6种不同的mRNA剪接异构体, 其编码的氨基酸序列均具有Ikaros家族典型的锌指结构域且与硬骨鱼类Ikaros氨基酸序列同源性较高(70.6%—93.7%)。Ikaros基因在尼罗罗非鱼各组织中均有表达, 在血液中的表达量最高, 其次为胸腺、脾脏和头肾。人工感染无乳链球菌后, 血液、胸腺、脾脏、头肾中Ikaros基因的相对表达量均显著上调, 并在48h达到峰值, 这表明Ikaros基因参与调控尼罗罗非鱼抵御无乳链球菌的免疫应答反应。研究可为进一步探索Ikaros基因在罗非鱼抗病原感染中的作用机制奠定理论基础。     

The CD8alpha gene locus is regulated by the Ikaros family of proteins

Ikaros family members are important regulatory factors in lymphocyte development. Here we show that Ikaros may play an important role in CD4 versus CD8 lineage commitment decisions by demonstrating: (1) that it binds to regulatory elements in the endogenous CD8alpha locus in vivo using thymocyte chromatin immunoprecipitations, (2) that Ikaros suppresses position effect variegation of transgenes driven by CD8 regulatory elements, and (3) that mice with reduced levels of Ikaros and Aiolos show an apparent increase in CD4 populations with immature phenotype, i.e., cells that failed to activate the CD8alpha gene locus. We propose that Ikaros family members function as activators of the CD8alpha gene locus and that their associated activities are critical for appropriate chromatin remodeling transitions during thymocyte differentiation and lineage commitment.     

Eos: a novel member of the Ikaros gene family expressed predominantly in the developing nervous system

We identified a novel member of the Ikaros gene family, which has critical roles in the development of lymphoid lineages. This gene, which we named Eos, was expressed predominantly in the developing central and peripheral nervous system. Eos protein could interact with itself and Ikaros protein through its C-terminal portion in the yeast two hybrid assay. These findings suggested that Eos may have important roles in neural development similarly to the Ikaros family in the development of hemolymphoid tissue.