DNMT1 Promotes Genome Methylation and Early Embryo Development in Cockroaches

Abstract

Summary The influence of DNA methylation on gene behavior and its consequent phenotypic effects appear to be very important, but the details are not well understood. Insects offer a diversity of DNA methylation modes, making them an excellent lineage for comparative analyses. However, functional studies have tended to focus on quite specialized holometabolan species, such as wasps, bees, beetles, and flies. Here, we have studied DNA methylation in the hemimetabolan insect Blattella germanica . In this cockroach, a gene involved in DNA methylation, DNA methyltransferase 1 ( DNMT1 ) , is expressed in early embryogenesis. In our experiments, RNAi of DNMT1 reduces DNA methylation and impairs blastoderm formation. Using reduced representation bisulfite sequencing and transcriptome analyses, we observed that methylated genes are associated with metabolism and are highly expressed, whereas unmethylated genes are related to signaling and show low expression. Moreover, methylated genes show greater expression change and less expression variability than unmethylated genes.

Dnmt1a is essential for gene body methylation and the regulation of the zygotic genome in a wasp

“…However, there was a clear bias in the methylation status of the DEGs and their direction of expression change. For example, 1201 out of 1331 (90%) of the down-regulated transcripts were derived from methylated genes in the middle blastoderm stage, while 1227/1413 (87%) upregulated transcripts came from unmethylated genes (Fig 4A , S3 The strong over-representation of methylated genes among down-regulated genes following Nv-Dnmt1a pRNAi fits well with previous observations in insects connecting DNA methylation with high and stable gene expression [31,33,44]. Furthermore, we have found that the magnitude of the reduction in expression was significantly correlated with the degree of lost methylation after pRNAi (Fig 4C, Spearman's rank correlation coefficient = 0.37, P < 2.2e-16).…”

“…In contrast to vertebrates, DNA methylation occurs almost exclusively at gene bodies in insects [30][31][32][33]. Thus, such insect model systems have the potential to make significant contributions in understanding the role of GBM in development.…”

Insights into the genomic evolution of insects from cricket genomes

“…Nevertheless, based on our data, we cannot determine whether the methylated genes are highly conserved because they are methylated, or because they perform basic functions that may be regulated by DNA methylation events. In the cockroach Blattella germanica, DNA methyltransferase enzymes and genes with low CpGo/e values show an expression peak during the maternal to zygotic transition 64 , and functional analysis has shown that the DNA methyltransferase 1 is essential for early embryo development in this cockroach 65 . These results in cockroaches, together with our observations, leads us to speculate that at least in Polyneopteran species, DNA methylation might contribute to the maternal zygotic transition by regulating essential genes involved in DNA replication, transcription, and translation.…”

Dnmt1a is essential for gene body methylation and the regulation of zygotic genome activation in the wasp

“…Comparison of orthologous gene expression between plants species or populations that had either maintained or lost GBM capability revealed little or no effect of GBM on expression levels of ancestrally methylated genes, indicating that GBM may have no appreciable effect on transcription (48)(49)(50). In insects, knockdown of DNMT1 orthologs lead to the loss GBM in the roach Blatella and the milkweed bug Oncopeltus (29,51). In the roach, loss of DNMT1 led to disruption of methylated gene expression levels, but no bias toward reduced expression was observed, while in the milkweed bug no change in gene expression levels was observed for any genes (29,51).…”

“…In insects, knockdown of DNMT1 orthologs lead to the loss GBM in the roach Blatella and the milkweed bug Oncopeltus (29,51). In the roach, loss of DNMT1 led to disruption of methylated gene expression levels, but no bias toward reduced expression was observed, while in the milkweed bug no change in gene expression levels was observed for any genes (29,51).…”