(A) Effect on epigenome stability. ZBTB43 facilitates the process of de novo DNA methylation in the fetal male germ cells. Top row: In wild type prospermatogonia ZBTB43 binds at PPR sequences that exist in the Z-DNA structure and changes the DNA structure. By doing this, ZBTB43 creates B-DNA which can be recognized as substrate by methyltransferase enzymes. DNA methylation establishment occurs normally at PPR-rich DNA regions at the fetal stage, and CpG methylation persists through the spermatozoa stage. Bottom row: In the Zbtb43^−/− mutant prospermatogonia that lacks ZBTB43 protein, PPRs remain in the Z-DNA structure, and do not undergo de novo DNA methylation. Hypomethylation of PPRs is detected in prospermatogonia and sperm. (B) Effect on genome stability. Compared with the wild type cells (top row), Zbtb43^−/− mutant prospermatogonia (bottom row) exhibit speckles of γH2AX in immunohistochemical analysis, indicating that in the absence of ZBTB43 DNA double strand breaks occur due to the Z-DNA structure in these cells in vivo. These breaks may result in genomic deletions or rearrangements, because ZBTB43 binding sites are highly mutagenic in mammalian mutation assays.