Light-regulated nuclear localization of phytochromes

Phytochrome is a soluble protein that regulates various responses of plants to light. Not all but most of the phytochrome responses are accompanied by changes in the pattern of gene expression. Upon light activation, phytochrome is imported into the nucleus by the nuclear localization activity of the carboxy-terminal half of the molecule. In darkness, the amino-terminal chromophoric domain suppresses this activity to retain the molecule in the cytoplasm. In the nucleus, light-activated phytochrome forms speckles whose biological function remains unclear.     

光敏色素与转录因子结合直接调控植物基因表达和发育

植物的光控发育一直是植物学中一个非常活跃的研究领域,是近该领域又取得重大突破性进展,人们通过酵母双杂交技术克隆到在体内与光敏色素相互作用的转录因子,并证实被光活化的光敏色素直接进入细胞核与转录因子结构合启动基因表达,本文就此研究进展作简要介绍。     

Light-dependent translocation of a phytochrome B-GFP fusion protein to the nucleus in transgenic Arabidopsis

Phytochrome is a ubiquitous photoreceptor of plants and is encoded by a small multigene family. We have shown recently that a functional nuclear localization signal may reside within the COOH-terminal region of a major member of the family, phytochrome B (phyB) (Sakamoto, K., and A. Nagatani. 1996. Plant J. 10:859-868). In the present study, a fusion protein consisting of full-length phyB and the green fluorescent protein (GFP) was overexpressed in the phyB mutant of Arabidopsis to examine subcellular localization of phyB in intact tissues. The resulting transgenic lines exhibited pleiotropic phenotypes reported previously for phyB overexpressing plants, suggesting that the fusion protein is biologically active. Immunoblot analysis with anti-phyB and anti-GFP monoclonal antibodies confirmed that the fusion protein accumulated to high levels in these lines. Fluorescence microscopy of the seedlings revealed that the phyB-GFP fusion protein was localized to the nucleus in light grown tissues. Interestingly, the fusion protein formed speckles in the nucleus. Analysis of confocal optical sections confirmed that the speckles were distributed within the nucleus. In contrast, phyB-GFP fluorescence was observed throughout the cell in dark-grown seedlings. Therefore, phyB translocates to specific sites within the nucleus upon photoreceptor activation.     

Vimentin binds IRAP and is involved in GLUT4 vesicle trafficking

Cysteine-rich protein 2 (CRP2) is a cofactor for smooth muscle cell (SMC) differentiation. Here, we examined the mechanism of CRP2 distribution dynamics during SMC differentiation. CRP2 protein directly associated with F-actin through its N-terminal LIM domain and Gly-rich region, as determined by ELISA. In undifferentiated cells that contain few actin stress fibers, CRP2 was broadly distributed throughout the whole cell, including the nucleus. After induction of SMC differentiation, CRP2 localized to actin stress fibers as they formed. The stress fiber-localized CRP2 entered the nucleus because of induced actin depolymerization. These CRP2 dynamics were reproduced by in silico simulation. CRP2 localization dynamics, which affect CRP2 function, are regulated by the formation of actin stress fibers in conjunction with SMC differentiation.     

ZmJAZ与ZmMYC2的BiFC互作研究

JAZ(jasmonate ZIM-domain)蛋白是茉莉酸(jasmonic acid,JA)信号途径中关键的负调控因子,明确JAZ蛋白和MYC2之间的结合关系对整个JA信号通路至关重要.通过qRT-PCR筛选了在籽粒中较特异表达的ZmJAZ4、生殖器官中高表达的ZmJAZ8以及组成型表达的ZmJAZ12,利用玉米...     

Phytochrome-interacting factors have both shared and distinct biological roles

Phytochromes are plant photoreceptors that perceive red and far-red light. Upon the perception of light in Arabidopsis, light-activated phytochromes enter the nucleus and act on a set of interacting proteins, modulating their activities and thereby altering the expression levels of ～10% of the organism’s entire gene complement. Phytochromeinteracting factors (PIFs) belonging to Arabidopsis basic helix-loop-helix (bHLH) subgroup 15 are key interacting proteins that play negative roles in light responses. Their activities are post-translationally countered by light-activated phytochromes, which promote the degradation of PIFs and directly or indirectly inhibit their binding to DNA. The PIFs share a high degree of similarity, but examinations of pif single and multiple mutants have indicated that they have shared and distinct functions in various developmental and physiological processes. These are believed to stem from differences in both intrinsic protein properties and their gene expression patterns. In an effort to clarify the basis of these shared and distinct functions, we compared recently published genome-wide ChIP data, developmental gene expression maps, and responses to various stimuli for the various PIFs. Based on our observations, we propose that the biological roles of PIFs stem from their shared and distinct DNA binding targets and specific gene expression patterns.     

Whirly转录因子研究进展

Whirly蛋白是广泛存在于植物细胞内的一种转录因子。它既能与单链DNA结合,也能与RNA结合,无论在细胞核还是在质体内都有着广泛而复杂的生物学功能。本文概述了Whirly蛋白的结构、种类、分布及其作用机制,并重点讨论了其在细胞核及质体内的功能,最后对Whirly蛋白研究中需要解决的问题做了展望。     

Nuclear distribution of claudin-2 increases cell proliferation in human lung adenocarcinoma cells

Claudin-2 is expressed in human lung adenocarcinoma tissue and cell lines, although it is absent in normal lung tissue. However, the role of claudin-2 in cell proliferation and the regulatory mechanism of intracellular distribution remain undefined. Proliferation of human adenocarcinoma A549 cells was decreased by claudin-2 knockdown together with a decrease in the percentage of S phase cells. This knockdown decreased the expression levels of ZONAB and cell cycle regulators. Claudin-2 was distributed in the nucleus in human adenocarcinoma tissues and proliferating A549 cells. The nuclear distribution of ZONAB and percentage of S phase cells were higher in cells exogenously expressing claudin-2 with a nuclear localization signal than in cells expressing claudin-2 with a nuclear export signal. Nuclear claudin-2 formed a complex with ZO-1, ZONAB, and cyclin D1. Nuclear distribution of S208A mutant, a dephosphorylated form of claudin-2, was higher than that of wild type. We suggest that nuclear distribution of claudin-2 is up-regulated by dephosphorylation and claudin-2 serves to retain ZONAB and cyclin D1 in the nucleus, resulting in the enhancement of cell proliferation in lung adenocarcinoma cells.