Abstract
Malaria parasites cause disease through repeated cycles of intraerythro-cytic proliferation. Within each cycle, several rounds of DNA replication produce mul-tinucleated forms, called schizonts, that undergo segmentation to form daughter merozoites. Upon rupture of the infected cell, the merozoites egress to invade new erythrocytes and repeat the cycle. In human malarial infections, an antibody response specific for the Plasmodium falciparum protein PF3D7_1021800 was previously associated with protection against malaria, leading to an interest in PF3D7_1021800 as a candidate vaccine antigen. Antibodies to the protein were reported to inhibit egress, resulting in it being named schizont egress antigen-1 (SEA1). A separate study found that SEA1 undergoes phosphorylation in a manner dependent upon the parasite cGMP-dependent protein kinase PKG, which triggers egress. While these findings imply a role for SEA1 in merozoite egress, this protein has also been implicated in kinetochore function during schizont development. Therefore, the function of SEA1 remains unclear. Here, we show that P. falciparum SEA1 localizes in proximity to centromeres within dividing nuclei and that conditional disruption of SEA1 expression severely impacts the distribution of DNA and formation of merozoites during schizont development, with a proportion of SEA1-null merozoites completely lacking nuclei. SEA1-null schizonts rupture, albeit with low efficiency, suggesting that neither SEA1 function nor normal segmentation is a prerequisite for egress. We conclude that SEA1 does not play a direct mechanistic role in egress but instead acts upstream of egress as an essential regulator required to ensure the correct packaging of nuclei within merozoites. IMPORTANCE Malaria is a deadly infectious disease. Rationally designed novel thera-peutics will be essential for its control and eradication. The Plasmodium falciparum protein PF3D7_1021800, annotated as SEA1, is under investigation as a prospective component of a malaria vaccine, based on previous indications that antibodies to SEA1 interfere with parasite egress from infected erythrocytes. However, a consensus on the function of SEA1 is lacking. Here, we demonstrate that SEA1 localizes to dividing parasite nuclei and is necessary for the correct segregation of replicated DNA into individual daughter merozoites. In the absence of SEA1, merozoites develop defectively, often completely lacking a nucleus, and, consequently, egress is impaired and/or aberrant. Our findings provide insights into the divergent mechanisms by which intraerythrocytic malaria parasites develop and divide. Our conclu-sions regarding the localization and function of SEA1 are not consistent with the hy-pothesis that antibodies against it confer protective immunity to malaria by blocking merozoite egress.
| Original language | English (US) |
|---|---|
| Article number | e03377-20 |
| Pages (from-to) | 1-16 |
| Number of pages | 16 |
| Journal | mBio |
| Volume | 12 |
| Issue number | 2 |
| DOIs | |
| State | Published - Mar 1 2021 |
Funding
We thank Rita Tewari, along with everyone in the Blackman, Deu, Holder, and Treeck laboratories at the Crick Institute, for helpful conversations and technical advice. We are particularly grateful to Ellen Knuepfer and Judith Green for sharing antibody reagents. All experiments were designed and carried out by A.J.P., with the exception of the EM imaging, which was performed by C.B. and R.A.L. under the instruction of C.B., and the mass spectrometry, which was carried out by P.A.F. Instructions for using the iSIM instrument and analysis of the data were provided by M.J.R., while H.R.S. and R.A.F. provided electron microscopy resources. Overall supervision was provided by M.J.B., D.A.B., and A.P.S. This research was funded in whole, or in part, by the Wellcome Trust. For the purpose of Open Access, the author has applied a CC BY public copyright license to any Author Accepted Manuscript version arising from this submission. This work was also supported by funding to M.J.B. from the Francis Crick Institute (https://www.crick.ac.uk/), which receives its core funding from Cancer Research UK (FC001043; https://www.cancerresearchuk.org), the UK Medical Research Council (FC001043; https://www.mrc.ac.uk/), and the Wellcome Trust (FC001043; https://wellcome.ac.uk/). The work was also supported by Wellcome Trust grant 106239/Z/14/A (A.J.P. and M.J.B.), Wellcome Trust grant 106240/Z/14/Z (D.A.B.), and Medical Research Council grant MR/P010288/1 (C.B., H.R.S., R.A.F., and M.J.B.). This research was funded in whole, or in part, by the Wellcome Trust. For the purpose of Open Access, the author has applied a CC BY public copyright license to any Author Accepted Manuscript version arising from this submission. This work was also supported by funding to M.J.B. from the Francis Crick Institute (https://www.crick.ac.uk/), which receives its core funding from Cancer Research UK (FC001043; https://www .cancerresearchuk.org), the UK Medical Research Council (FC001043; https://www.mrc.ac .uk/), and the Wellcome Trust (FC001043; https://wellcome.ac.uk/). The work was also supported by Wellcome Trust grant 106239/Z/14/A (A.J.P. and M.J.B.), Wellcome Trust grant 106240/Z/14/Z (D.A.B.), and Medical Research Council grant MR/P010288/1 (C.B., H.R .S., R.A.F., and M.J.B.).
Keywords
- CENP-C
- Egress
- Malaria
- Plasmodium falciparum
- Schizogony
- SEA1
ASJC Scopus subject areas
- Microbiology
- Virology
