# A Spinster-like Transporter at the Inner Membrane Complex is critical for Toxoplasma gondii cytokinesis, motility and invasion

## TL;DR

This study identifies a key transporter protein in Toxoplasma gondii that is essential for cell division, movement, and invading host cells.

## Contribution

The paper reveals TgDCT1 as a conserved lipid transporter critical for the inner membrane complex in Toxoplasma gondii and related parasites.

## Key findings

- TgDCT1 is localized to the daughter cell inner membrane complex and is essential for cytokinesis and motility.
- Pharmacological inhibition of SPNS2 phenocopies TgDCT1 depletion, suggesting a conserved lipid transport role.
- Transgenic complementation shows functional conservation of DCT1 across Apicomplexa species.

## Abstract

The Major Facilitator Superfamily (MFS) comprises a large and diverse group of membrane transport proteins involved in the translocation of metabolites across cellular membranes. The genome of Toxoplasma gondii encodes approximately 60 putative MFS transporters, yet the functions of most remain poorly characterized. Conserved across the superphylum Alveolata, the inner membrane complex (IMC) is a specialized peripheral membrane system essential for parasite replication, structural integrity, motility, and host cell invasion. Here, we identify Toxoplasma gondii Daughter Cell Transporter 1 (TgDCT1), a previously uncharacterized MFS transporter, as a critical regulator of daughter cell formation. TgDCT1 localizes predominantly to the daughter cell IMC and contains a predicted spinster-like MFS domain. Phylogenetic and structural analyses reveal that TgDCT1 is conserved across Alveolata, shares a canonical MFS fold with its Plasmodium falciparum orthologue, and exhibits striking structural similarity to the human sphingosine-1-phosphate (S1P) transporter SPNS2, suggesting an evolutionarily conserved role in lipid transport. Conditional depletion of TgDCT1 results in severe defects in cytokinesis, including disrupted IMC architecture, aberrant daughter cell morphology, and failure of plasma membrane abscission. Although TgDCT1-depleted parasites retain the capacity for microneme secretion and egress, they display profoundly impaired motility and host cell invasion, ultimately leading to arrest of the lytic cycle. Notably, pharmacological inhibition of the S1P transporter SPNS2 using the compounds 11i and 33p phenocopies TgDCT1 depletion, impairing parasite morphogenesis, intracellular replication, and division synchrony. Furthermore, transgenic complementation demonstrates that the spinster-like domain of the P. falciparum DCT1 orthologue can functionally substitute for TgDCT1, indicating that these transporters likely recognize the same substrate. Together, these findings establish TgDCT1 as a central regulator of lipid homeostasis required for IMC maturation, endodyogeny, and parasite propagation in Toxoplasma gondii and likely other Apicomplexa.

The inner membrane complex (IMC) is a unique cellular structure crucial for the replication, shape, and motility in Toxoplasma gondii, which causes widespread infections in humans and animals. Our study focuses on TgDCT1, a previously uncharacterized transporter protein specifically localized to the IMC of daughter parasites during cell division. TgDCT1 belongs to the Major Facilitator Superfamily of membrane transporters and possesses features indicative of a role in lipid transport. Notably, this transporter is conserved across multiple Alveolata, underscoring its evolutionary significance beyond Toxoplasma. Using various knockdown systems, we demonstrate that TgDCT1 is essential for IMC homeostasis; its depletion results in severe morphological defects, including abnormal cytokinesis and compromised IMC integrity. Although parasites lacking TgDCT1 can still exit host cells, their motility and invasion capabilities are dramatically impaired, preventing successful completion of the lytic cycle. These findings establish TgDCT1 as a key player in T. gondii development, suggesting that its transported substrate is vital for maintaining IMC structure and parasite viability. Targeting such critical transport mechanisms could open new avenues for therapeutic intervention against apicomplexan parasites.