Duplicated dnmt3aa and dnmt3ab DNA Methyltransferase Genes Play Essential and Non-Overlapped Functions on Modulating Behavioral Control in Zebrafish.

Yu-Heng Lai,Petrus Siregar,Erwei Hao,Gilbert Audira,Oliver B Villaflores,Michael Edbert Suryanto,Huan-Chau Lin,Sung-Tzu Liang,Chung-Der Hsiao,Omar Villalobos,Ken-Hong Lim

doi:10.3390/genes11111322

Abstract

DNA methylation plays several roles in regulating neuronal proliferation, differentiation, and physiological functions. The major de novo methyltransferase, DNMT3, controls the DNA methylation pattern in neurons according to environmental stimulations and behavioral regulations. Previous studies demonstrated that knockout of Dnmt3 induced mouse anxiety; however, controversial results showed that activation of Dnmt3 causes anxiolytic behavior. Thus, an alternative animal model to clarify Dnmt3 on modulating behavior is crucial. Therefore, we aimed to establish a zebrafish (Danio rerio) model to clarify the function of dnmt3 on fish behavior by behavioral endpoint analyses. We evaluated the behaviors of the wild type, dnmt3aa, and dnmt3ab knockout (KO) fish by the novel tank, mirror biting, predator avoidance, social interaction, shoaling, circadian rhythm locomotor activity, color preference, and short-term memory tests. The results indicated that the dnmt3aa KO fish possessed abnormal exploratory behaviors and less fear response to the predator. On the other hand, dnmt3ab KO fish displayed less aggression, fear response to the predator, and interests to interact with their conspecifics, loosen shoaling formation, and dysregulated color preference index ranking. Furthermore, both knockout fishes showed higher locomotion activity during the night cycle, which is a sign of anxiety. However, changes in some neurotransmitter levels were observed in the mutant fishes. Lastly, whole-genome DNA methylation sequencing demonstrates a potential network of Dnmt3a proteins that is responsive to behavioral alterations. To sum up, the results suggested that the dnmt3aa KO or dnmt3ab KO fish display anxiety symptoms, which supported the idea that Dnmt3 modulates the function involved in emotional control, social interaction, and cognition.

Highlights

DNA methylation plays an important role in epigenetic modification [1]
From the morphometric analysis results, we found that the homozygotic mutants carrying either dnmt3aa or dnmt3ab gene deficiency were viable and displayed no significant difference in their outlook to the wild type AB strain (WT) zebrafish (Figure 2A,B)
(Figure 2D), and 5-hmC/5-methylated cytosines (mC) ratio (Figure 2F) displayed no significant difference in either dnmt3aa or dnmt3ab KO fish lines

Summary

Introduction

DNA methylation plays an important role in epigenetic modification [1]. The add on and off of methyl group onto DNA without altering protein-coding sequences is catalyzed by DNA methyltransferases (DNMTs) and demethylase (TETs) [2,3]. The family of Dnmt homolog genes, Dnmt, Dnmt, Dnmt3A, Dnmt3B, and Dnmt3L, have been identified in mammals [4,5]. Dnmt plays a role in DNA methylation maintenance, while Dnmt3a, Dnmt3b, and Dnmt3L take charge of performing de novo methylation [6,7,8]. Due to the importance of DNMTs in genomic modification, dysregulation on DNMTs may result in inherited diseases, such as chromosome instability [10], developmental abnormality [11], and cancer formation [12,13]

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