Increased sensitivity of various genes to endogenous DNase activity in terminal differentiating chick lens fibers

Applying modern Omic technologies to the Neuronal Ceroid Lipofuscinoses

The Neuronal Ceroid Lipofuscinoses are a group of severe and progressive neurodegenerative disorders, which generally present during childhood. With new treatments emerging on the horizon, there is a growing need to understand the specific disease mechanisms as well as identify prospective biomarkers for use to stratify patients and monitor treatment. The use of Omics technologies to NCLs has the potential to address this need. We discuss the recent use and outcomes of Omics to various forms of NCL including identification of interactomes, affected biological pathways and potential biomarker candidates. We also identify common pathways affected in NCL across the reviewed studies.

Chromatin degradation in differentiating fiber cells of the eye lens

During development, the lens of the eye becomes transparent, in part because of the elimination of nuclei and other organelles from the central lens fiber cells by an apoptotic-like mechanism. Using confocal microscopy we showed that, at the border of the organelle-free zone (OFZ), fiber cell nuclei became suddenly irregular in shape, with marginalized chromatin. Subsequently, holes appeared in the nuclear envelope and underlying laminae, and the nuclei collapsed into condensed, spherical structures. Nuclear remnants, containing DNA, histones, lamin B2, and fragments of nuclear membrane, were detected deep in the OFZ. We used in situ electrophoresis to demonstrate that fragmented DNA was present only in cells bordering the OFZ. Confocal microscopy of terminal deoxynucleotidyl transferase (TdT)-labeled lens slices confirmed that DNA fragmentation was a relatively late event in fiber differentiation, occurring after the loss of the nuclear membrane. DNA fragments with 3'-OH or 3'-PO(4) ends were not observed elsewhere in the lens under normal conditions, although they could be produced by pretreatment with DNase I or micrococcal nuclease, respectively. Dual labeling with TdT and an antibody against protein disulfide isomerase, an ER-resident protein, revealed a distinct spatial and temporal gap between the disappearance of ER and nuclear membranes and the onset of DNA degradation. Thus, fiber cell chromatin disassembly differs significantly from classical apoptosis, in both the sequence of events and the time course of the process. The fact that DNA degradation occurs only after the disappearance of mitochondrial, ER, and nuclear membranes suggests that damage to intracellular membranes may be an initiating event in nuclear breakdown.

DNA strand breakage during physiological apoptosis of the embryonic chick lens: free 3' OH end single strand breaks do not accumulate even in the presence of a cation-independent deoxyribonuclease

Epithelial cells from the lens equator differentiate into elongated fiber cells. In the final steps of differentiation, the chromatin appears quite condensed and chromatin breakdown into nucleosomes occurs. DNA breaks due to an endodeoxyribonuclease activity corresponding to at least two polypeptides of 30 and 40 kDa have been identified. To identify the nature and the developmental appearance of initial breaks, nick translation reaction was followed both biochemically and in situ in fiber and epithelial cells from chick embryonic lenses. There is no accumulation of single-strand breaks (SSB) with 3'OH ends in lens fiber cells during embryonic development. Such damage can be increased in these cells by treatment with DNAase I indicating the absence of an inhibitor of the nick translation reaction in fiber cells. However, there are indications of the presence of DNA breaks with blocked termini when the phosphatase activity of nuclease P1 is used. The presence of breaks is also indicated by the large amounts of (ADP-ribose)n found in lens fibers particularly at 11 days of embryonic development (E11) as ADP-ribosyl transferase binds to and is activated by DNA strand breaks. Incubation of lens cells in vitro, which causes nucleosomal fragmentation only in fiber cells, produces SSB with 3'OH ends in both epithelia and fibers. Incubation for short periods, observed in experiments in situ, induces SSB first in the central fiber nuclei, which are late in differentiation. This may indicate that these SSB play a physiological role. Long incubations produce larger numbers of SSB in epithelia than fibers. The SSB in the fibers may have been converted into double-strand breaks (D SB), seen as nucleosomal fragments, and therefore no longer act as substrates for nick translation. The nuclease activity responsible for SSB production is independent of divalent cations and could be implicated in lens terminal differentiation.

Decrease of DNA per cell during development of the lens in chickens

Developmental changes in the amount and conformation of DNA in chicken lens were studied. For this, DNA in situ in lens fiber cell nuclei of chickens was examined by microfluorometry with Hoechst 33258 (Hoe) fluorochrome. On 1 M NaCl-aided Hoe staining, by which the amount of DNA can be determined accurately, the fluorescence intensity of lens fiber cells was found to decrease with no change in that of the lens epithelial cells during development. On the contrary, on normal NaCl-free Hoe staining the fluorescence intensity of the lens cells was found to increase gradually during development. These results suggest that during development the amount of DNA in lens fiber cells decreases in association with some change in its conformation.