Inducible dCas12a tool widens CRISPR gene control in malaria parasite

Malaria remains one of humanity’s most stubborn infectious diseases, claiming more than 600,000 lives in 2024, with the vast majority of deaths caused by a single parasite: Plasmodium falciparum. Despite decades of research, roughly half of the more than 5,000 genes encoded in the parasite’s genome still lack any functional annotation, and resistance to front-line antimalarial drugs, including artemisinin, continues to spread across Africa and Asia. Against this backdrop, a research team reporting in the journal iScience has unveiled a new genetic tool that promises to accelerate the hunt for the parasite’s vulnerabilities: an inducible, CRISPR-based gene regulation system built on the enzyme Cas12a rather than the more familiar Cas9.

The new platform belongs to a family of techniques known as CRISPR interference and activation, or CRISPRi/a. Unlike standard CRISPR gene editing, which cuts DNA and permanently alters the genome, CRISPRi/a uses a catalytically inactive version of a Cas protein, often called a dead Cas, that can bind DNA without slicing it. When fused to regulatory proteins and guided to a gene’s promoter region by short RNA molecules, these dead enzymes can dial gene expression up or down. This is especially valuable for studying essential genes, which cannot simply be deleted because doing so kills the organism. By tuning expression levels instead, researchers can probe what a gene does while keeping the parasite alive.

The team’s previous work had established inducible dCas9-based CRISPRi/a systems in P. falciparum, fusing the dead Cas9 to PfGCN5, a histone acetyltransferase that activates genes, or to PfSir2a, a histone deacetylase that represses them. But Cas9 has a fundamental limitation in this parasite: it requires a short DNA motif called NGG, the protospacer adjacent motif or PAM, to bind its targets. The P. falciparum genome is roughly 80 percent adenine and thymine, making NGG sites relatively scarce, particularly in the promoter regions where gene regulation happens. Cas12a, by contrast, recognizes a T-rich PAM called TTTV, and the new study shows this makes an enormous difference.

Systematic scanning of the parasite’s reference genome revealed that Cas12a PAM sites are about 2.5 times more abundant than Cas9 sites overall, and roughly five times more common in annotated promoter regions. After filtering out guide RNAs with predicted off-target effects, the researchers found approximately seven times more usable Cas12a-based guide RNAs than Cas9-based ones in promoters, amounting to about eight clean targets per gene compared with roughly three for Cas9. Using the invasion gene eba-175 as a test case, the 804-base-pair promoter region contained nearly eight times as many Cas12a target sites as Cas9 sites. This expanded targeting space gives researchers far more flexibility in designing experiments.

Building the new system required adapting the inducible architecture the group had previously developed for dCas9. A green fluorescent protein cassette, followed by a transcriptional terminator, is inserted upstream of the dCas12a fusion gene, blocking its expression. This blocking cassette is flanked by loxP sites. When researchers add rapamycin to the culture, a split Cre recombinase reassembles and excises the floxed cassette, switching expression from GFP to the dCas12a fusion protein. The team used a nuclease-inactive LbCas12a variant from the bacterium Lachnospiraceae, tagged for detection, and introduced the constructs into a DiCre-expressing P. falciparum 3D7 line. Within 30 hours of a two-hour rapamycin pulse, GFP fluorescence vanished and the dCas12a fusion proteins became detectable by Western blot, confirming tight, leak-free induction. The fusion proteins did not impair parasite growth on their own.

To benchmark performance, the researchers targeted Pfatg18, an autophagy gene they had previously regulated with dCas9. Three guide RNAs positioned 70, 580, and 1,396 base pairs upstream of the gene’s start codon were tested in both the repression and activation lines. In the dCas12a-Sir2a parasites, Pfatg18 transcripts fell to between 10 and 30 percent of control levels, causing marked growth defects. In the dCas12a-GCN5 line, two of the guides boosted expression roughly 2.5-fold and 1.8-fold, which also retarded growth, echoing earlier findings that Pfatg18 overexpression disrupts autophagy homeostasis. A parallel experiment on eba-175 showed repression to as low as 15 percent of normal and activation up to 3.6-fold, demonstrating that the Cas12a platform matches or exceeds its Cas9 predecessor on both sides of the regulatory dial.

One of Cas12a’s signature features proved especially powerful: the enzyme processes its own guide RNA transcripts. Because Cas12a has intrinsic RNase activity, multiple guide sequences can be strung together in a single array, separated by direct repeat sequences, and the enzyme itself chops the long transcript into individual guides. The researchers assembled three-guide arrays for both Pfatg18 and eba-175. For interference, the arrays outperformed individual guides: the Pfatg18 array pushed repression below 10 percent, and the eba-175 array drove expression down to roughly 4 percent, substantially stronger than any single guide achieved. Activation via arrays was effective but did not exceed the best individual guides, likely because histone acetylation at promoters can become saturated. This multiplexing capacity dramatically simplifies construct design for pooled genetic screens.

The system’s real test came with Pfset7, a lysine methyltransferase gene that previous knockout attempts had failed to disrupt, suggesting it is essential. Three guide RNAs targeting the Pfset7 promoter reduced transcript levels by 50 to 70 percent, with corresponding drops in protein confirmed by antibodies raised against the recombinant PfSET7 protein. The consequences were striking: parasites with strong knockdown showed severe growth inhibition, egress defects in 39 to 64 percent of schizonts, meaning the mature parasites struggled to burst from their host red blood cells, and invasion efficiency of purified merozoites dropped by 35 to 52 percent. Intriguingly, the reverse experiment told the same story from the other direction. Overexpressing Pfset7 by 3.7 to 6.6-fold also caused growth defects, presumably because excessive methylation of the gene’s target proteins disrupts essential cellular processes. This bidirectional evidence, in which both depletion and excess impair the parasite, provides unusually strong confirmation that PfSET7 is essential and likely orchestrates egress and invasion, mirroring the role of its homolog in Toxoplasma gondii.

The researchers acknowledge limitations. Not every guide RNA worked; of nine guides tested, one activation guide and two interference guides had little effect, and one guide reduced mRNA without reducing protein levels, possibly reflecting compensatory translation. Guide performance did not correlate with predicted RNA folding stability, so empirical optimization remains necessary, though the abundance of Cas12a target sites makes it easy to test multiple guides or deploy arrays. Off-target effects, minimized through stringent computational filtering with tools like CRISPOR and CHOPCHOP, cannot be entirely excluded and require validation. Still, the combination of inducibility, bidirectional control, and multiplexing positions the dCas12a platform as a scalable foundation for forward genetic screens under drug pressure, heat shock, or nutrient stress, conditions where conditional gene requirements often emerge.

The implications extend beyond basic biology. Because the system can modulate, rather than abolish, gene function, it opens a window onto the roughly half of the parasite’s genome that remains uncharacterized, including essential genes that knockout approaches cannot touch. The plasmids have been deposited with Addgene, and the parasite lines are available to the community, lowering barriers to adoption. As artemisinin resistance consolidates in Africa and chloroquine resistance long ago became global, tools that rapidly expose new drug targets are urgently needed. A tunable, multiplexable genetic dial for the world’s deadliest malaria parasite may prove to be exactly the kind of instrument that turns genomic data into therapeutic insight.

Subject of Research: Development of an inducible dCas12a-based CRISPR interference and activation system for functional genomics in Plasmodium falciparum

Article Title: Inducible dCas12a system expands CRISPRi/a capabilities for functional genomics in malaria parasite Plasmodium falciparum

Article References: Lucky, A. B., Li, X., Kobakhidze, G., Gonzales, J. L., Wang, C., Cui, L., Dong, G., & Miao, J. (2026). Inducible dCas12a system expands CRISPRi/a capabilities for functional genomics in malaria parasite Plasmodium falciparum. iScience, 29(10), Article 117704. https://doi.org/10.1016/j.isci.2026.117704

Image Credits: AI Generated

DOI: Not provided

Keywords: CRISPRi, CRISPRa, dCas12a, Plasmodium falciparum, malaria, functional genomics, PfSET7, DiCre, gene regulation, Cas12a, epigenetics, drug targets