Parasitology: CRISPR for Cryptosporidium

Abstract

Study of the diarrhoea-causing pathogen Cryptosporidium has been hindered by a lack of genetic-modification and culture tools. A description of genome editing and propagation methods for the parasite changes this picture.

Figure 1. Modification and culture of Cryptosporidium

The strong-walled oocyst form of Cryptosporidium parasites can be isolated from the faeces of infected calves. Oocysts can be induced to excyst to release the sporozoite form, which will infect cultured mammalian epithelial cells, but the sporozoites undergo only one or two rounds of replication before they die. Vinayak et al.1 have improved on this limited in vitro system in two ways. They have developed techniques for genetically modifying the sporozoite form — using electroporation to introduce foreign DNA in the form of a plasmid bearing the sequences required for CRISPR-based genome editing. And they show that these modified sporozoites will replicate when directly transplanted into the intestines of mice, and can be recovered as modified oocysts, which can be collected from mouse faeces for analysis in culture, or used to inoculate new mice to maintain the line indefinitely.