Grevelding, C. | Search bioRxiv

bioRxiv2026

The histone code of love: epigenetics of maturation of gonads in the human blood fluke Schistosoma mansoni

Schistosoma mansoni is a parasitic flatworm that has two, genetically determined, sexes. We used aggregated data of 8 posttranslational histone modifications (ChIP-Seq), chromatin accessibility (ATAC-Seq), transcription (RNA-Seq) and genome feature annotations to decipher the histone code of genes involved in the differentiation of schistosome gonads (i.e. female ovaries and male testes). We show schistosome gonads express at least two classes of protein coding genes: H3K4me3-positive genes that display canonical features of eukaryotic protein-coding genes such as peaks of H3K4me3 at the transcription start sites (TSS) and increases in histone acetylation marks towards the transcription end site (TES), but also a non-canonical H3K9/27me3 plateau just upstream of the TSS. H3K4me3 enrichment at the TSS is highly predictive for transcription strength in these genes compared to a second class of protein coding genes (H3K4me3-negative genes) that do not display this pattern and is characterised by absence of the investigated histone marks at TSS and TES. This is indicative of the existence of hitherto unknown, potentially schistosome-specific histone marks in these genes. The absence of H3K4me3 at the TSS is not associated with inducible or stable gene expression in the gonads. Instead, gene ontology analysis indicates that H3K4me3-positive genes are related to functions which typically govern processes such as metabolism or signal transduction while H3K4me3-negative genes are dedicated to cell communication or immune responses. Second, individual histone modifications and their combinations are associated with functional features of the schistosome genome, known as "chromatin colours". In H3K4me3-positive genes, there is clear co-linearity of 3 colours, which strongly suggests a functional role for histone modifications in the control of transcription pre-initiation, promotor release, and transcription termination. Third, there are striking chromatin structure changes during maturation of the gonads in all genomic features including protein-coding and non-protein coding genes as well as repetitive sequences. The nature of these changes is different in both sexes. H3K36me3 and H3K9me3, as well as H3K23ac and H3K9ac show the strongest variations. Last, we show that pharmacological inhibition of histone demethylation activity by IOX1 leads to a concentration-dependent separation ("divorce") of schistosome couples confirming the importance of H3K36/H3K9 methylation for pairing maintenance and indicating histone demethylases as a potential drug target family. Collectively, our findings offer unprecedented insights into histone codes and chromatin dynamics governing the reproductive development of S. mansoni gonads.

developmental biology↗

bioRxiv2022

Targeted insertion of reporter transgene into a gene safe harbor in human blood fluke, Schistosoma mansoni

The identification and characterization of genomic safe harbor sites (GSH) aims to facilitate consistent transgene activity without disruption to the host cell genome. We combined genome annotation and chromatin structure analysis by computational approach to predict the location of four GSHs in the human blood fluke, Schistosoma mansoni, a major infectious pathogen of the tropics. Introduction of a transgene into the egg of the parasite was accomplished using CRISPR/Cas-assisted homology-directed repair and overlapping guide RNAs. Gene editing efficiencies of 24% and transgene-encoded fluorescence of 75% of gene-edited schistosome eggs were observed. These outcomes advance functional genomics for schistosomes by providing a tractable path towards transgenic helminths using homology directed repair-catalyzed transgene insertion. This approach should be adaptable to helminths generally. MotivationFunctional genomics methods are needed in the arena of the Neglected Tropical Diseases, especially for helminth parasites, to facilitate basic and transformational studies to improve global public health. Gain-of-function phenotypes would be valuable in this context. Hence, the motivation for this investigation was to identify a genome safe harbor (GSH) site in the chromosomes of the human blood fluke, Schistosoma mansoni and, in a pilot approach, and to develop methods for transgene insertion and methods to characterize transgene performance following homology directed insertion at the schistosome GSH. The progress reported here can be expected to advance functional genomics for species of the Platyhelminthes - including model, free living species of planarians, and should be adaptable to helminths generally.

molecular biology↗