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

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.

Phenotypically Anchored mRNA and miRNA Expression Profiling in Zebrafish Reveals Flame Retardant Chemical Toxicity Networks

“…This corroborated with our finding that chlorinated phosphates likely do not disrupt neurotransmitter activity. The present study also suggested an epigenetically driven FRC-induced neurotoxicity since dnmt3aa, a regulator of methylation of transcripts that drive neuronal development (Lai et al, 2020), was overexpressed by several FRCs. Such epigenetic regulation of FRC neurotoxicity was also reflected in a previous study, which showed that TDCIPP [Tris(1,phosphate], a chlorinated OPFRC that induced behavioral deficits in zebrafish, altered dnmt3aa transcript levels (Li et al, 2020).…”

Dnmt3aa But Not Dnmt3ab Is Required for Maintenance of Gametogenesis in Nile Tilapia

“…It is worth noting that homozygous mutation of Dnmt3a in mice was fatal, whereas mutation of either dnmt3aa or dnmt3ab in zebrafish and tilapia was viable [28,29,70]. In this study, different spatial-temporal expression profiles of dnmt3aa and dnmt3ab, up-regulation of dnmt3ab in dnmt3aa −/− gonad and up-regulation of dnmt3aa in dnmt3ab −/− gonad were observed.…”

“…These studies suggest that dnmt3aa and dnmt3ab may play important roles in gonadal development of fish, however, their detailed expression profiles during the sex determination and differentiation and gonadal development of teleost are unclear. Recently, some research groups reported the mutation of dnmt3aa and dnmt3ab in zebrafish, demonstrating their critical function on behavior regulation [28], temperature adaptation [29] and brain neural development [30]. Nevertheless, the roles of dnmt3aa and dnmt3ab in gonadal development of fish remain unknown.…”

Dnmt3aa but Not Dnmt3ab Is Required for Maintenance of Gametogenesis in Nile Tilapia (Oreochromis niloticus)

“…However, recent studies on zebrafish have shown that the homozygous mutants of dnmt3aa or dnmt3ab are viable. Dnmt3aa and dnmt3ab are demonstrated to have essential and non-overlapped functions in modulating behavioral control, and dnmt3aa or dnmt3ab mutation fish display anxiety symptoms [ 30 ]. In addition, some groups have demonstrated the roles of dnmt3aa or dnmt3ab in regulating developmental thermal plasticity, and the phenotypic effects of dnmt3aa and dnmt3ab are additive [ 31 ].…”

“…These studies suggest that dnmt3aa and dnmt3ab may play important roles in the gonadal development of fish; however, their detailed expression profiles during the sex determination and differentiation and gonadal development of teleosts are unclear. Recently, some research groups reported the mutation of dnmt3aa and dnmt3ab in zebrafish, demonstrating their critical function on behavior regulation [ 30 ], temperature adaptation [ 31 ] and brain neural development [ 32 ]. Nevertheless, the roles of dnmt3aa and dnmt3ab in the gonadal development of fish remain unknown.…”