Extended chromatin fibers and chromatin organization

The salivary glands of Brontocoris tabidus (Heteroptera: Pentatomidae): Morphology and secretory cycle

Brontocoris tabidus (Signoret) (Heteroptera: Pentatomidae) is a zoophytophagous insect used for biological control in agriculture and forest systems because its nymphs and adults feed on insects and plants. The predatory Pentatomidae insert the mouthparts into the prey, releasing saliva to paralysis and kills the insect, as well as digest body parts to be sucked in a preliminary extra-oral digestion. In a short period of time, this insect shows the ability to feed again, suggesting the existence of a constant and abundant secretory cycle in the salivary glands. This study evaluated the morphological, histochemical and ultrastructural changes of the salivary glands of B. tabidus in fed and starved insects. The salivary complex of this predatory bug has a pair of bilobed salivary glands and a pair of tubular accessory salivary glands. The accessory glands have the lumen lined by a thick non-cuticular layer rich in glycoproteins. The secretory cells of the B. tabidus principal salivary glands have constant secretory activity, with each lobe producing different substances. The physiological processes that occur in the salivary gland of B. tabidus indicate that the insect needs to feed constantly, corroborating the potential of this insect to be used in biological control programs.

Polarization microscopy of extended chromatin fibers

Analysis of the formation of extended chromatin fibers (ECFs) in response to the action of gravity following lysis by hypertonic and detergent solutions is a useful technical procedure relevant for studies of the positioning of particular DNA signals on chromatin filaments. Additionally, if toluidine blue molecules are allowed to bind electrostatically to available DNA phosphates on ECFs, the birefringence brightness generated in these filaments, as observed by polarization microscopy, facilitates the description of the frequency of ECF formation and extension of the chromatin filaments generated. Thus, different patterns of DNA-nuclear matrix protein associations related to varying transcriptional activities and chromatin organization in isolated cells can be assessed. A technique for producing ECFs in different isolated cell types under variable physiological and/or pathological conditions is detailed in this chapter.

Polyploidy and chromatin remodeling in hepatocytes from insulin-dependent diabetic and normoglycemic aged mice

Changes in polyploidization, chromatin supraorganization, and chromatin accessibility were investigated in hepatocytes collected from adult, nonobese diabetic (NOD) mice with increasing hyperglycemia and compared with adult normoglycemic controls and 56-week-old normoglycemic BALB/c mice. Our goal was to determine the changes in ploidy degrees and chromatin characteristics in mouse hepatocytes that are associated with insulin-dependent diabetes and to detect similarities in these aspects with those verified with aging, with greater accuracy than previous studies. Image analysis of Feulgen-stained nuclei revealed changes in ploidy degrees and chromatin supraorganization. Chromatin accessibility was assessed with micrococcal nuclease (MNase) digestion. Increased polyploidy was associated with increasing levels of glycemia, and this trend toward polyploidy was found even under normoglycemic conditions in NOD mice. Although high degrees of ploidy were also detected in aged BALB/c mice, the magnitude of polyploidy was not the same magnitude as that in the diabetic mice. While there was increased homogeneity of chromatin packaging with increasing polyploidy under conditions of severe hyperglycemia (and even under conditions of normoglycemia) in NOD mice, an inverse relationship was observed in aged BALB/c mice. Chromatin accessibility to MNase increased under severe hyperglycemia and advanced age, but it was much higher in the diabetic mice. In conclusion, although similarities in polyploidy were observed between the hepatocytes from increasingly hyperglycemic adult mice and those from normoglycemic aged mice, the relationship between chromatin remodeling and increases in ploidy degrees was not the same between the hepatocytes of these two groups. These findings demonstrate that strict similarities between diabetes and aging are not always true at the cellular level. This discordance is likely due to differences in the metabolic state of mouse hepatocytes during aging and diabetic conditions consequent to specificities in their gene regulatory programs.

Atomic force microscopy on chromosomes, chromatin and DNA: a review

The purpose of this review is to discuss the achievements and progress that has been made in the use of atomic force microscopy in DNA related research in the last 25 years. For this review DNA related research is split up in chromosomal-, chromatin- and DNA focused research to achieve a logical flow from large- to smaller structures. The focus of this review is not only on the AFM as imaging tool but also on the AFM as measuring tool using force spectroscopy, as therein lays its greatest advantage and future. The amazing technological and experimental progress that has been made during the last 25 years is too extensive to fully cover in this review but some key developments and experiments have been described to give an overview of the evolution of AFM use from 'imaging tool' to 'measurement tool' on chromosomes, chromatin and DNA.