rnaset2 mutant zebrafish model familial cystic leukoencephalopathy and reveal a role for RNase T2 in degrading ribosomal RNA

Abstract

T2-family acidic endoribonucleases are represented in all genomes. A physiological role for RNase T2 has yet to be defined for metazoa. RNASET2 mutation in humans is linked with a leukoencephalopathy that arises in infancy characterized by cortical cysts and multifocal white matter lesions. We now show localization of RNASET2 within lysosomes. Further, we demonstrate that loss of rnaset2 in mutant zebrafish results in accumulation of undigested rRNA within lysosomes within neurons of the brain. Further, by using high field intensity magnetic resonance microimaging, we reveal white matter lesions in these animals comparable to those observed in RNASET2-deficient infants. This correlates with accumulation of Amyloid precursor protein and astrocytes at sites of neurodegeneration. Thus we conclude that familial cystic leukoencephalopathy is a lysosomal storage disorder in which rRNA is the best candidate for the noxious storage material.

Evidence for autophagy-dependent pathways of rRNA turnover inArabidopsis

“…Mutations affecting Danio rerio (zebrafish) RNASET2 also resulted in animals that accumulate rRNA in lysosomes, particularly in neurons, and this accumulation caused white-matter lesions in the fish brain, again indicating that rRNA degradation is necessary for cellular homeostasis in nonstarvation conditions. 18 The involvement of Arabidopsis RNS2 and zebrafish RNASET2 in housekeeping rRNA turnover is consistent with the hypothesis that the conservation of the RNase T2 family in all eukaryotes is due to a conserved housekeeping role performed by these enzymes. 20 In fact, RNase T2 enzymes have been shown to participate in rRNA degradation in conditions of nutritional stress in addition to the housekeeping role in plants and animals described above.…”

“…64,65 Studies in multiple systems have found RNS2 orthologs to be important for the degradation of rRNA. Mutant alleles of RNASET2 are associated with accumulation of undigested rRNA within lysosomes in zebrafish and human neurons, 18,66 and rRNA is a cellular substrate for the RNase T2 enzymes of unicellular eukaryotes such as yeast and Tetrahymena during nutrient starvation. 22,23 We previously showed that under normal growth conditions rns2-2 and antisense RNS2 plants had rRNA with extended half-life, indicating that rRNA is a substrate for RNS2 in plants.…”

“…16 While ribophagy has not yet been specifically studied in other eukaryotes, mounting evidence suggests that the process could be conserved in plants and animals and that starvation is not required for ribophagy to occur. [17][18][19] In addition to an important role in response to nutrient deficiency, rRNA turnover also seems to be necessary for maintenance of cellular homeostasis during periods of normal growth. In Arabidopsis thaliana mutants lacking RNS2 (At2g39780), a nonspecific endoribonuclease of the RNase T2 family that resides in the endoplasmic reticulum and the vacuole, rRNA has a longer half-life than in wild-type (WT) plants, indicating that this enzyme is necessary for normal rRNA decay.…”

RNASET2 is required for ROS propagation during oxidative stress-mediated cell death

“…30,39 Prior studies have established roles for RNASET2 in tumor progression, vitiligo, and neurodevelopmental development abnormalities. 32,39,47 Our study provides new insights into the function of this lysosomal enzyme as a regulator of pathophysiological oxidative stress responses and adds to a growing body of evidence that the lysosome and its components are essential for integrating a wide array of metabolic stimuli into cell fate decisions. 48,49 Future studies to establish the precise substrates of RNASET2 will shed important light on the mechanisms through which it functions to control cellular oxidative tone.…”

“…27,32 To test whether palm treatment caused degradation of rRNA, we isolated total RNA from CHO and 2B1 cells following palm treatment and measured 18S and 28S rRNA species. Although the abundance of 18S rRNA was Figure 3) were treated with 500 μM palm for 10 h. Cytoplasmic RNA was isolated by sequential detergent extraction, reverse transcribed, and analyzed by qRT-PCR for rpL13a snoRNAs relative to actin (c-e).…”