Degradation of nuclear DNA by DNase II‐like acid DNase in cortical fiber cells of mouse eye lens

Abstract

The eye lens is composed of fiber cells that differentiate from epithelial cells on its anterior surface. In concert with this differentiation, a set of proteins essential for lens function is synthesized, and the cellular organelles are degraded. DNase II‐like acid DNase, also called DNase IIβ, is specifically expressed in the lens, and degrades the DNA in the lens fiber cells. Here we report that DNase II‐like acid DNase is synthesized as a precursor with a signal sequence, and is localized to lysosomes. DNase II‐like acid DNase mRNA was found in cortical fiber cells but not epithelial cells, indicating that its expression is induced during the differentiation of epithelial cells into fiber cells. Immunohistochemical and immunocytochemical analyses indicated that DNase II‐like acid DNase was colocalized with Lamp‐1 in the lysosomes of fiber cells in a relatively narrow region bordering the organelle‐free zone, and was often found in degenerating nuclei. A comparison by microarray analysis of the gene expression profiles between epithelial and cortical fiber cells of young mouse lens indicated that some genes for lysosomal enzymes (cathepsins and lipases) were strongly expressed in the fiber cells. These results suggest that the lysosomal system plays a role in the degradation of cellular organelles during lens cell differentiation.

Deletion of Autophagy-related 5 (Atg5) and Pik3c3 Genes in the Lens Causes Cataract Independent of Programmed Organelle Degradation

“…Several potential mechanisms have been reported, which include the ubiquitin-proteasome system (28,41,42), 15-lipoxygenase (43), and DNase II-like acid DNase (DLAD) (44). Among them, DLAD, a lysosomal DNase (45,46), is required for degradation of nuclear DNA in the lens (44). Thus, it is likely that the lysosome is involved in degradation of nuclear DNA in a manner different from any known types of autophagy.…”

A Novel Method For Purifying a DNase From Lysosomal Fraction From Human Small Intestine

“…They are active and present in lysosome (but found in other organelles) and believed to act as a barrier to transfection for DNA or vectors entering the cell by endocytosis [8] and may degrade foreign DNAs and play a role in the replication of DNA [9]. Recent studies have identified many DNases that are active at neutral pH such as caspase-activated DNase (CAD) [10], and endonuclease G [11] that are found in mammals, though a few researchers have concentrated on insect acid [12]. The function of DNases within the small intestine is debated and very few researchers purified DNases from small intestine.…”

DNA Degradation and Its Defects

“…DLAD (DNase II-like acid DNase, also called DNase IIb) has a 38% amino acid sequence identity with DNase II (Shiokawa and Tanuma 1999) and is also localized to the lysosomes (Nakahara et al 2007). Unlike DNase II, which is ubiquitously expressed in various tissues and cells, DLAD is specifically expressed in fiber cells of the optic lens (Fig.…”

“…As the epithelial cells differentiate into fiber cells, they synthesize lens-fiber-specific proteins such as crystallins. The DLAD gene is also activated during this differentiation process (Nakahara et al 2007). …”

“…These properties associated with the strong inflammation by IFN-b are similar to those in DNase II-null mice. Nakahara et al 2007;reprinted, with permission. ) tion factors IFN regulatory factor (IRF)3/IRF7 and NF-kB.…”