Abstract
Purpose: :
The role of WDR36 in the pathogenesis of primary open angle glaucoma (POAG) remains controversial. Originally identified as the causative gene at locus GLC1G, subsequent studies identified reported disease causing mutations in control patients. While this has shown WDR36 may not be causative for POAG, strong correlations between POAG and polymorphisms within WDR36 have continued to be found. Overall, evidence suggests that WDR36 may act as a modifier of POAG, but studies in animal models will be crucial for clarifying how and if WDR36 acts in this capacity. We have used the zebrafish for this purpose, and have previously shown that vertebrate WDR36 is necessary for proper 18S ribosomal RNA (rRNA) maturation. The purpose of this study was to further investigate the function of wdr36 and to determine potential mechanisms for its role in POAG.
Methods: :
A zebrafish line containing a viral insertion within wdr36 and antisense morpholinos (MOs) targeting wdr36 were used to assess knockdown phenotypes. MOs designed against p53 were used to assess interactions between wdr36 and p53. Phenotypes were assessed by light and electron microscopy, Northern blot, immuno-based markers, PCR, FACS and histology.
Results: :
Electron miscroscopy showed that the defects in 18S rRNA maturation found with loss of wdr36 causes disruption of the nucleolus. Typically, nucleolar disruption results in activation of the p53 pathway. Activation of p53 was confirmed with loss of Wdr36 in zebrafish mutants and morphants. Interestingly; during early development, an N-terminal truncation isoform of p53 (d113p53) was transcriptionally upregulated while full length p53 was not. d113p53 leads to activation of cell cycle arrest markers but does not activate apoptosis. A delay in the cell cycle was confirmed by BrdU labeling and DNA-FACS analysis. Later in development full length p53 and apoptosis are upregulated and the morphology of the eye is disrupted. Overall, a clear interaction between dysfunction of Wdr36 and activation of the p53 pathway was observed.
Conclusions: :
The role of WDR36 as a modifier of POAG has remained unclear. In this study, we have uncovered a potential mechanism for the involvement of WDR36 in POAG pathogenesis. Retinal ganglion cells (RGCs) are lost due to apoptotic cell death in POAG, and we have shown that Wdr36 interacts with p53, a key regulator of apoptosis. This has lead to our proposed model: RGCs cannot react appropriately to stressors (such as high IOP) due to defects in WDR36 and/or the p53 pathway which may then act in concert to cause the RGC cell death characteristic of POAG.
Keywords: genetics • apoptosis/cell death • ribosomal RNA