Import Of Histones Research Articles

HD2 overexpression induces dwarfism and elevated histone deacetylase activities in transgenic Ananas comosus variety MD2

Plant tissue culture has served as one of the most efficient biotechnological tools to mass produce high quality major crops. Nevertheless, the use of this technique can result in the occurrence of somaclonal variation, which may be brought upon by genetic and/or epigenetic modulations. The epigenetic modulation of plant growth, particularly on the importance of histone deacetylation/acetylation on genome stability, transcriptional regulation, as well as plant development, has been reported in several species such as Arabidopsis, rice, and maize. However, the information on its role in regulating the growth of major crops such as pineapple is still lacking. Previously, we had reported that supplementation of high cytokinin in the tissue culture media and exposure to salinity and abscisic acid (ABA) resulted in the production of somaclonal variants that exhibited dwarf phenotypes, and that these occurrences were associated with epigenetic modulation via the involvement of histone deacetylases (HDACs). Thus, in the present study, we aimed to further elucidate and verify the involvement of histone deacetylation in the occurrence of dwarfism in tissue culture-derived pineapple plants, through HD2 gene overexpression. AtHD2 gene from Arabidopsis thaliana was synthesized and expressed in phenotypically normal Ananas comosus. Transformation efficiency was also studied, and application of 200-µM acetosyringone was observed to be more efficient than 500 µM vanillin by 10%. The transgenic plants were observed to exhibit dwarfed phenotypes and showed significantly high HDAC enzyme activities. Ploidy evaluation of the transgenic plants showed no ploidy change had occurred in the samples and remained as 2n. The relative expression level of AtHD2 was also higher (3.2-fold up-regulation) in the transgenic plants compared to the wild type plants. Collectively, these results indicate that HDACs indeed played an essential role in the response of A. comosus towards abiotic stress, and that this phenomenon is epigenetically regulated.

The Role of Chromatin in Adenoviral Vector Function

Vectors based on adenovirus (Ad) are one of the most commonly utilized platforms for gene delivery to cells in molecular biology studies and in gene therapy applications. Ad is also the most popular vector system in human clinical gene therapy trials, largely due to its advantageous characteristics such as high cloning capacity (up to 36 kb), ability to infect a wide variety of cell types and tissues, and relative safety due to it remaining episomal in transduced cells. The latest generation of Ad vectors, helper‑dependent Ad (hdAd), which are devoid of all viral protein coding sequences, can mediate high-level expression of a transgene for years in a variety of species ranging from rodents to non-human primates. Given the importance of histones and chromatin in modulating gene expression within the host cell, it is not surprising that Ad, a nuclear virus, also utilizes these proteins to protect the genome and modulate virus- or vector‑encoded genes. In this review, we will discuss our current understanding of the contribution of chromatin to Ad vector function.

Single Molecule Studies of Nuclear Transport

The translocation of single biomolecules through nanopores is one of the most fundamental processes of life. For example, the import of histones into the cell nucleus via the nuclear pore complex (NPC) is crucial for DNA condensation (1,2). We aim to gain a deeper understanding of NPC translocation on a single molecule level by combining optical tweezers with patch clamp techniques. This gives us the unique possibility to analyze the interaction forces between a biological macromolecule and the NPC while measuring the relevant time scales by electrophysiological recordings. We present preliminary results on the characterisation of the properties of NPCs concerning mode and duration of macromolecular translocation. Nuclei extracted from the syntactical coconut cocos nucifera are one model system. We demonstrate the selectivity of the NPC using an import signal tagged with GFP. We determine the conductance of a single nuclear pore to be approximately 490pS. Our results allow for estimation of the nuclear pore density to be between one and four per μm2. From observations of the ionic current across the pores, we are able to observe gating and to derive the translocation time of cargo across single NPCs . As a technical development towards nuclear pore force spectroscopy we introduce optical fiber illumination for real-time tracking of optically trapped particles. We demonstrate video-based fluctuation analysis of a single colloid at 10,000 Hz in order to study the dynamics of an attached biological macromolecule with microsecond time resolution (3-5).

A Rosetta (hi)stone?

DNA in the eukaryotic nucleus is coiled onto nucleosomes assembled generally as an octamer of well-studied subunits: H2A, H2B, H3 and H4. Several variants of core histones exist in many organisms, and these presumably have alternative functions. The importance of histones in DNA function has been slowly unraveled over many years, and the metaphor of a histone ‘code’ of various amino acid modifications is now rooted in concepts of epigenetic mechanisms. In shifting the focus towards understanding histone variants, a new study of histone H3.3 reveals another fold in the fabric of histone protein function [1].

ATP-dependent chromatin-remodeling complexes.

The importance of histones and chromatin structure in the regulation of eukaryotic gene transcription has become much more widely accepted over the past few years. It has been clear for a decade that histones contribute to the regulation of transcription both in vitro and in vivo (reviewed in references 14, 34, 50, 64, and 120). More recent studies have led to the striking observation that several protein complexes involved in transcription regulation can function, at least in part, by modifying histones or altering chromatin structure (for recent reviews, see references 3, 44, 49, 51, 52, 87, 100, and 119). While it is clear that many of these protein complexes have functions in addition to chromatin modification, they illustrate the importance of chromatin structure as a part of transcription regulation mechanisms. The most widely characterized chromatin-modifying complexes studied to date can be classified into two major groups, based on their modes of action, as follows: (i) ATP-dependent complexes, which use the energy of ATP hydrolysis to locally disrupt or alter the association of histones with DNA, and (ii) histone acetyltransferase (HAT) and histone deacetylase (HDAC) complexes, which regulate the transcriptional activity of genes by determining the level of acetylation of the amino-terminal domains of nucleosomal histones associated with them. This review will focus primarily on the ATP-dependent remodeling complexes. For recent reviews of HAT and HDAC complexes, see references 5, 20, 31, and 55. Here we provide an organized listing of the ATP-dependent chromatin-remodeling complexes described to date and illustrate the relationships between their subunits. We also review the data available with regard to their mechanisms of action and promoter targeting as well as regulation of their activity. Finally, we examine the relationship between these complexes and the HAT complexes.