A putative replicative form of the abutilon mosaic virus (gemini group) in a chromatin-like structure

Summary The putative replicative form of the abutilon mosaic virus (AbMV), a geminivirus, was purified from infected plants. It was shown to consist of a bipartite genome of 2660 and 2640 bp. This double-stranded DNA has a closed or relaxed circular conformation and part of it is packed in nucleoprotein complexes with a chromatin-like structure. Similarities between the geminiviruses and the animal simian virus 40 are discussed against this back-ground.Cloning was performed under L2/B1 conditions according to the licence of the ZKBS 1526/1This article is based on a doctoral study by A.A. and T.F. in the Faculty of Biology, University of Hamburg     

Bronchoconstriction: a potential missing link in airway remodelling

In asthma, progressive structural changes of the airway wall are collectively termed airway remodelling. Despite its deleterious effect on lung function, airway remodelling is incompletely understood. As one of the important causes leading to airway remodelling, here we discuss the significance of mechanical forces that are produced in the narrowed airway during asthma exacerbation, as a driving force of airway remodelling. We cover in vitro, ex vivo and in vivo work in this field, and discuss up-to-date literature supporting the idea that bronchoconstriction may be the missing link in a comprehensive understanding of airway remodelling in asthma.     

Identification and Characterization of Bmi-1-responding Element within the Human p16 Promoter

Bmi-1, the first functionally identified polycomb gene family member, plays critical roles in cell cycle regulation, cell immortalization, and cell senescence. Bmi-1 is involved in the development and progression of carcinomas and is a potent target for cancer therapy. One important pathway regulated by Bmi-1 is that involving two cyclin-dependent kinase inhibitors, p16^Ink4a and p19^Arf, as Bmi-1 represses the INK4a locus on which they are encoded. A close correlation between the up-regulation of Bmi-1 and down-regulation of p16 has been demonstrated in various tumors; however, how Bmi-1 regulates p16 expression is not clear. In this study, we revealed that Bmi-1 regulates the expression of p16 by binding directly to the Bmi-1-responding element (BRE) within the p16 promoter. The BRE resided at bp −821 to −732 upstream of the p16 ATG codon. BRE alone was sufficient to allow Bmi-1-mediated regulation of the CMV promoter. Bmi-1 typically functions by forming a complex with Ring2; however, regulation of p16 was independent of Ring2. Chromatin immunoprecipitation sequencing of Bmi-1-precipitated chromatin DNA revealed that 1536 genes were targeted by Bmi-1, including genes involved in tissue-specific differentiation, cell cycle, and apoptosis. By analyzing the binding sequences of these genes, we found two highly conserved Bmi-1-binding motifs, which were required for Bmi-1-mediated p16 promoter regulation. Taken together, our results revealed the molecular mechanism of Bmi-1-mediated regulation of the p16 gene, thus providing further insights into the functions of Bmi-1 as well as a sensitive high-throughput platform with which to screen Bmi-1-targeted small molecules for cancer therapy.     

Spatial genome organization

The linear sequence of genomes exists within the three-dimensional space of the cell nucleus. The spatial arrangement of genes and chromosomes within the interphase nucleus is nonrandom and gives rise to specific patterns. While recent work has begun to describe some of the positioning patterns of chromosomes and gene loci, the structural constraints that are responsible for nonrandom positioning and the relevance of spatial genome organization for genome expression are unclear. Here we discuss potential functional consequences of spatial genome organization and we speculate on the possible molecular mechanisms of how genomes are organized within the space of the mammalian cell nucleus.     

Follicle population, cumulus mucification, and oocyte chromatin configuration during the periovulatory period in the female dog

This study was designed to describe the follicular population present on the canine ovary (Canis familiaris) during the preovulatory period and essentially the changes in oocyte size, mucification, and chromatin configuration occurring from before the luteinizing hormone (LH) surge up to postovulation. In a first experiment, ovaries of beagle bitches were collected before (n = 21) or after LH surge but before ovulation (post-LH surge/preovulation stage, n = 24) as determined using hormone (LH, estradiol, progesterone) assays and ultrasonography. All large (>2 mm) follicles were measured and punctured. The numbers of oocytes collected per follicle and the degree of cumulus mucification were recorded. In a second experiment, ovaries were similarly collected before (n = 13) and after the LH surge but before ovulation (n = 11) as well as after ovulation as determined by ultrasonography (n = 9). Chromatin configuration of the oocytes was observed by DNA staining and confocal microscopy. In Experiment 1, before the LH peak, an average of 13.5 ± 0.7 follicles per bitch (total 284 follicles) were detected, and the maximal follicle diameter reached 6.5 mm. Large follicles were observed already in this period of the cycle and as early as when progesterone was still below 0.5 ng/mL. After the LH peak but before ovulation, 11.0 ± 0.7 follicles were present (total 264 follicles). Fully mucified cumulus cells were observed only in follicles larger than 4 mm. Multi-oocytic follicles represented 7% (before LH peak) and 4% (after LH peak) of the follicular population. In Experiment 2, all the oocytes were at the germinal vesicle (GV) stage, but three chromatin configurations could be distinguished: diffuse, partly grouped, and fully grouped chromatin. The proportion of oocytes with fully grouped chromatin increased with the follicular diameter and the time in estrus, the maximum being observed after the LH peak. These results suggest that (1) before LH peak, follicles are already of large diameter, similar to the ones at ovulation; (2) the ability for cumulus mucification is acquired during the late steps of follicular growth; (3) three GV patterns may be observed during the periovulatory period.