Leg regeneration is epigenetically regulated by histone H3K27 methylation in the cricket Gryllus bimaculatus

Hemimetabolous insects such as the cricket Gryllus bimaculatus regenerate lost tissue parts using blastemal cells, a population of dedifferentiated proliferating cells. The expression of several factors that control epigenetic modification is upregulated in the blastema compared with differentiated tissue, suggesting that epigenetic changes in gene expression might control the differentiation status of blastema cells during regeneration. To clarify the molecular basis of epigenetic regulation during regeneration, we focused on the function of the Gryllus Enhancer of zeste [Gb’E(z)] and Ubiquitously transcribed tetratricopeptide repeat gene on the X chromosome (Gb’Utx) homologues, which regulate methylation and demethylation of histone H3 lysine 27 (H3K27), respectively. Methylated histone H3K27 in the regenerating leg was diminished by Gb’E(z)^RNAi and was increased by Gb’Utx^RNAi. Regenerated Gb’E(z)^RNAi cricket legs exhibited extra leg segment formation between the tibia and tarsus, and regenerated Gb’Utx^RNAi cricket legs showed leg joint formation defects in the tarsus. In the Gb’E(z)^RNAi regenerating leg, the Gb’dac expression domain expanded in the tarsus. By contrast, in the Gb’Utx^RNAi regenerating leg, Gb’Egfr expression in the middle of the tarsus was diminished. These results suggest that regulation of the histone H3K27 methylation state is involved in the repatterning process during leg regeneration among cricket species via the epigenetic regulation of leg patterning gene expression.