Targeted insertion and reporter transgene activity at a gene safe harbor of the human blood fluke, Schistosoma mansoni

Abstract

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.