Parasite Kinase on the Endoplasmic Reticulum Revealed as a Master Switch for Calcium, Motility and Virulence

Neospora caninum is one of the most economically damaging parasites that cattle producers have never heard of. An obligate intracellular relative of the malaria parasite, this single-celled apicomplexan is a leading cause of spontaneous abortion in dairy and beef herds worldwide, and there is no effective drug or vaccine available to control it. Now a team at China Agricultural University has identified a single parasite kinase that appears to sit at the hub of the organism’s motility, calcium signaling, developmental programming and, crucially, its ability to cause disease. The discovery, published in Parasites & Vectors, offers a fresh molecular handle on a pathogen that has stubbornly resisted control efforts.

The protein in question is NcDYRK2, a member of the dual-specificity tyrosine phosphorylation-regulated kinase family. DYRKs are ancient and highly conserved serine/threonine kinases found across eukaryotes, where they orchestrate processes as varied as cell cycle progression, cellular differentiation and signal transduction. While their functions in model organisms such as yeast, flies and mammals have been mapped in considerable detail, the roles of DYRK family members in apicomplexan parasites have remained largely unexplored. Given that neosporosis lacks effective chemotherapy, the researchers reasoned that identifying parasite kinases governing virulence and development could expose promising drug targets that would be absent, or at least very different, in the host animal.

To interrogate NcDYRK2’s function, the team turned to CRISPR-Cas9 gene editing. They generated a knockout strain lacking the dyrk2 gene, and in parallel constructed complemented parasites in which the gene was restored, allowing any observed defects to be attributed specifically to the deleted kinase rather than to off-target effects of editing. They also engineered parasites carrying an epitope-tagged version of the native protein, which enabled them to pinpoint where NcDYRK2 resides inside the cell by immunofluorescence microscopy. The answer was striking: the kinase localizes predominantly to the endoplasmic reticulum, the membrane network that in most eukaryotes serves as a major intracellular calcium store.

That ER localization proved to be a meaningful clue rather than a curiosity. When the researchers compared the knockout parasites with wild-type controls across a battery of standard fitness assays, a paradoxical picture emerged. Loss of NcDYRK2 significantly enhanced gliding motility, the distinctive substrate-crawling movement that apicomplexans use to traverse tissues and invade new cells, and it also boosted plaque formation, a composite readout of a parasite population’s ability to spread and destroy a host cell monolayer. Yet the more fundamental steps of the parasite’s life cycle inside the host cell were untouched: host cell invasion, intracellular replication and egress all proceeded normally in the knockout strain.

Because gliding motility in apicomplexans is tightly governed by intracellular calcium, the team next examined calcium dynamics directly using real-time fluorescence imaging. The Δdyrk2 parasites showed elevated basal concentrations of intracellular Ca²⁺, suggesting that in the absence of the kinase the parasite’s calcium homeostasis is chronically disturbed. Even more telling was the response to ionomycin, an ionophore that floods the cytosol with calcium: knockout parasites mounted a diminished Ca²⁺ response compared with wild type. Together these observations indicate that NcDYRK2 helps regulate both the resting calcium set point and the parasite’s capacity to mobilize calcium from internal stores, consistent with its position on the endoplasmic reticulum.

To understand how a single kinase could produce such broad phenotypic effects, the researchers performed RNA sequencing on knockout and wild-type parasites. The transcriptomic comparison revealed extensive gene expression alterations: 554 differentially expressed genes in total, of which 393 were downregulated and 161 upregulated. Principal component analysis cleanly separated the knockout group from the parental controls along the first principal component, which accounted for over 70 percent of the total variance, and biological replicates clustered tightly, with intra-group correlation coefficients above 0.986, underscoring the robustness of the dataset.

Among the downregulated genes were several with well-known roles in stage differentiation, a process of central importance to the parasite’s biology and transmission. Bradyzoite-associated genes including BPK1, CST1, MCP3, MCP4 and MAG2 were all transcriptionally reduced in the knockout strain, as was MIC17A, a gene associated with the merozoite stage. Bradyzoites are the slowly dividing, cyst-forming stage that persists chronically in infected animals, and the cyst wall proteins they produce are what allow the parasite to hide from the immune system and from drugs. The downregulation of this entire developmental program implicates NcDYRK2 as a regulator of stage differentiation, not merely a housekeeping enzyme.

The calcium signaling machinery itself also bore the fingerprint of NcDYRK2 loss. Calmodulin genes CAM1 and CAM3 were transcriptionally upregulated in the knockout parasites, a pattern that could reflect compensatory responses to the disrupted calcium balance, while PIPLCβ, encoding phosphoinositide phospholipase C beta, an enzyme that generates calcium-mobilizing second messengers, was downregulated. Quantitative reverse transcription PCR confirmed these transcriptional changes independently. The coordinated alteration of calmodulins and phospholipase signaling provides a mechanistic bridge between the kinase’s ER location, the observed calcium dysregulation and the hypermotile phenotype of the knockout parasites.

The most consequential result came from experiments in living animals. When mice were infected with the knockout parasites, virulence was markedly attenuated compared with wild-type infection, and quantitative PCR of brain tissue at 40 days post-infection revealed significantly reduced brain cyst burdens. This finding ties the in vitro molecular phenotypes directly to pathogenicity: a parasite that cannot properly regulate its calcium signaling and cannot fully express its bradyzoite developmental program is also a parasite that establishes fewer chronic infections in the brain. All animal work was conducted under the approval of the Institutional Animal Care and Use Committee of China Agricultural University, with measures taken to minimize animal suffering.

Taken together, the study establishes NcDYRK2 as a critical coordinator of calcium-dependent motility, stage-specific gene expression and virulence in N. caninum. What makes the kinase especially interesting from a drug discovery standpoint is its unusual profile of dispensability and necessity: the parasite can invade, replicate and exit host cells without it, yet it loses much of its disease-causing capacity in its absence. Inhibiting such a target would not need to kill the parasite outright in culture but could instead defang it in the host, blunting tissue migration and chronic cyst formation, the hallmarks of neosporosis. The work also adds to a growing appreciation that apicomplexan parasites have co-opted conserved eukaryotic kinase families for parasite-specific purposes, and that the endoplasmic reticulum, long studied as a calcium store, functions in these organisms as a signaling platform integrated with motility and differentiation. The research was supported by the National Natural Science Foundation of China, and the authors suggest that NcDYRK2 now merits further evaluation as a candidate target for future anti-neosporosis strategies, a prospect that could not come soon enough for an industry losing calves to this silent abortifacient.

Subject of Research: Role of the endoplasmic reticulum-associated kinase NcDYRK2 in regulating calcium dynamics, motility, development and virulence in Neospora caninum

Article Title: Endoplasmic reticulum-associated NcDYRK2 regulates Ca2⁺ dynamics, motility, and development gene expression in Neospora caninum

Article References: Yang, S., Wang, X., Yu, S., Fu, Y., Liu, Q., & Liu, J. (2026). Endoplasmic reticulum-associated NcDYRK2 regulates Ca2⁺ dynamics, motility, and development gene expression in Neospora caninum. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07681-x

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07681-x

Keywords: Neospora caninum, NcDYRK2, calcium signaling, endoplasmic reticulum, gliding motility, transcriptomics, virulence, bradyzoite differentiation, CRISPR-Cas9, apicomplexan parasites, kinases, neosporosis