Abstract
Purpose:
De novo DNA methylation is a process in which unmethylated regions of DNA become methylated, and this correlates with silencing of the genes nearby the methylation sites. Previous research has demonstrated a requirement for de novo methylation during organogenesis in vertebrate model systems; however, little is known about the roles of de novo methylation in tissue-specific cell differentiation when populations of unspecialized somatic cells adopt their final morphology and functions. In the lens, proliferative lens epithelial (LE) cells undergo differentiation to become lens fiber (LF) cells. Despite this drastic cellular transition, how LE-specific genes are silenced and LF-specific genes become activated remains unknown. The purpose of this study is to investigate the roles of de novo methyltransferases in regulating lens development.
Methods:
Expression analyses of all six members of the dnmt3 gene family (dnmt3 - dnmt8) were performed in zebrafish by in situ hybridization to assess the spatio-temporal expression patterns of these genes during lens development. To address function during lens development, antisense morpholino oligos (MOs) were utilized to transiently knockdown two of the dnmt family genes that show expression in or near the lens (dnmt3 and dnmt4). Additionally, site-specific mutations in these genes were generated using transcription activator-like endonucleases (TALENs).
Results:
All six dnmt3 family genes are expressed in zebrafish eye. Expression of dnmt6 and dnmt8, homologues of mammalian Dnmt3A, are restricted to the ganglion cell layer and inner nuclear layer of the retina, while the other four genes (dnmt3, dnmt4, dnmt5, and dnmt7) are expressed in the lens and ciliary marginal zone (CMZ) adjacent to the lens. Knockdown of dnmt3 or dnmt4 by MO injection resulted in cataracts and retention of nuclei in lens fibers. Preliminary data suggest that these nucleated cells might retain LE characteristics.
Conclusions:
Gene expression analyses and functional tests indicate that members of the dnmt3 family of de novo methyltransferases function during lens development. Continued studies will elucidate the epigenetic mechanisms governing tissue-specific cell differentiation, and how de novo DNA methylation functions during lens development.
Keywords: 445 cataract •
497 development •
539 genetics