Microproteins, often abbreviated MPs, are proteins encoded by small open reading frames, or sORFs, that typically produce peptides shorter than 100 amino acids. For decades these tiny coding sequences were dismissed as genomic noise, too short to be considered real genes and too small to yield easily detectable protein products. That view has changed dramatically over the past several years, as researchers working on humans, plants and model organisms discovered that microproteins act as regulators of processes ranging from muscle development to stress responses. Well-known examples include the LITTLE ZIPPER proteins, abbreviated ZPR, which modulate plant transcription factor networks. Yet in protozoan parasites, the functional roles and evolutionary conservation of microproteins have remained poorly understood, a gap the Taiwanese team set out to close for one of medicine’s most persistent pathogens.

Trichomonas vaginalis is a particularly compelling subject for this kind of survey. The parasite infects an estimated hundreds of millions of people worldwide, causes trichomoniasis, and is associated with increased risks of adverse pregnancy outcomes and heightened susceptibility to HIV infection. Its genome is famously large and repetitive, which complicates standard annotation pipelines and makes it a plausible refuge for uncharted small genes. Because microproteins are short and often weakly expressed, standard omics approaches struggle to distinguish genuine microprotein-coding genes from random stretches of sequence. The researchers therefore designed a multi-layered validation strategy specifically intended to overcome the limitations of conventional methods, layering independent lines of evidence so that each candidate microprotein had to survive several rounds of scrutiny.

The foundation of the analysis was transcriptomic. The team integrated bulk RNA sequencing data from 22 isolates of Trichomonas vaginalis, allowing them to ask which small open reading frames were consistently transcribed across genetically distinct parasite strains rather than appearing in only one background. This cross-isolate approach delineated what the authors describe as a stable core microproteome of 918 microprotein candidates expressed consistently across the isolates. Within that set, 786 genes correspond to core-expressed microprotein genes, while 132 candidates derive from non-annotated small open reading frames located in regions of the reference genome that had never been assigned a gene. The consistent length distribution of the expressed microproteins across all 22 isolates, ranging from very short peptides up to the 100 amino acid cutoff, underscores how stable the composition of this expressed microproteome is across the species.

One of the most striking findings concerns evolutionary novelty. When the team evaluated sequence homology between the parasite’s microproteins and the human proteome using stringent BLASTp criteria, they found that approximately 93 percent of the 918 candidates lack significant similarity to any human protein. That figure matters for two reasons. Scientifically, it suggests that the majority of these microproteins are either lineage-specific innovations or have diverged so far from their metazoan counterparts that sequence-based detection fails, making them a rich hunting ground for novel biology. Translationally, the scarcity of human homologs raises the possibility that many of these molecules could be targeted therapeutically with a reduced risk of cross-reacting with the human host, an important consideration for any future drug or vaccine development program built on this resource.

Functional predictions add further texture to the picture. About 14 percent of the identified microproteins were predicted to be membrane-associated or secreted proteins, a category of particular interest because membrane and secreted molecules sit at the interface between the parasite and its host and are prime candidates for involvement in host-parasite interactions, immune evasion and adhesion. Functional enrichment analysis of the broader set indicated that the microproteins are primarily associated with intracellular anatomical structures, ribosomal components and organelles, hinting at roles in fundamental cellular processes rather than peripheral functions. InterProScan annotation of the full candidate set, provided in the study’s supplementary tables, catalogs the domains, gene ontology annotations and pathway assignments that will let other researchers prioritize candidates for experimental follow-up.

Transcription alone does not prove translation, so the team turned to liquid chromatography coupled with tandem mass spectrometry, LC-MS/MS, to confirm that microproteins are actually made. Working with protein extracts from the isolates ATCC 30236 and PRA98, separated by SDS-PAGE and processed through both in-gel and in-solution digestion workflows, the researchers confirmed the translation of 103 microproteins. Each of these detections rests on peptide spectrum matches linking observed mass spectra to predicted microprotein sequences, providing direct physical evidence that the genome’s small open reading frames are not merely transcribed but actively translated into stable protein products. The validation results, including the breakdown of in-gel and in-solution identifications, are published as supplementary data accompanying the paper.

The third pillar of the validation strategy was single-cell RNA sequencing, employed to assess how robustly microprotein transcripts are expressed at the level of individual cells. Bulk RNA sequencing can mask heterogeneity within a population, so a transcript that appears abundant on average might in fact be produced by only a small subset of cells. The scRNA-seq analysis of isolate ATCC 30236 demonstrated that 149 of the microprotein candidates are detected in more than 50 percent of individual cells, indicating that their expression is a widespread property of the parasite population rather than a niche feature of a few cells. Single-cell prevalence data for the full candidate set are provided in the study’s supplementary tables, giving future investigators a quantitative measure of expression robustness to weigh alongside transcript abundance measured in transcripts per million.

The study’s authors emphasize that this work provides the first comprehensive atlas of microproteins in Trichomonas vaginalis and establishes a valuable resource for future functional investigations. That framing is worth taking seriously, because an atlas of this kind changes the economics of follow-up research. Instead of each laboratory having to rediscover which small open reading frames are real, expressed and translated, investigators can now start from a curated list of 918 candidates, of which 103 have mass spectrometry evidence and 149 have single-cell expression support, and select targets based on predicted localization, homology status and expression pattern. The supplementary tables, which include genomic locations, molecular weights, isoelectric points, start codons and nucleotide sequences, are designed to make that triage straightforward.

Looking ahead, the open questions are considerable. What do these microproteins actually do inside the parasite’s cells? Are the membrane-associated and secreted members of the set involved in the host-parasite interplay that determines infection severity? Do the 132 candidates from previously unannotated intergenic regions represent a class of genes that standard pipelines have systematically missed, not just in this parasite but in related protists? The Taiwanese team, supported by grants from the National Science and Technology Council and Chang Gung Memorial Hospital, has provided the map; the territory now awaits exploration. For a pathogen that has long been managed with a narrow arsenal of therapies and continues to pose public health challenges worldwide, the discovery that nearly a thousand tiny, mostly human-dissimilar proteins are woven into its biology is an invitation to look again at what a parasite genome really contains.

Subject of Research: Proteogenomic identification of microproteins encoded by small open reading frames in the protozoan parasite Trichomonas vaginalis

Article Title: A comprehensive proteogenomic landscape of microproteins in Trichomonas vaginalis

Article References: Syu, J.-W., Luo, H.-W., Lin, R., Huang, P.-J., Lee, C.-C., Yeh, Y.-M., Chiu, C.-H., Ong, S.-C., & Tang, P. (2026). A comprehensive proteogenomic landscape of microproteins in Trichomonas vaginalis. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07669-7

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07669-7

Keywords: Trichomonas vaginalis, microproteins, small open reading frames, proteogenomics, LC-MS/MS, single-cell RNA sequencing, transcriptomics, parasite biology, host-parasite interactions, genome annotation, sexually transmitted infection, Parasites & Vectors

The study, led by Yasuaki Yanagawa and Ayako Okuhama of the AIDS Clinical Center at the National Center for Global Health and Medicine, together with colleagues in Tokyo and at Tokai University School of Medicine, examined stored blood samples from 1,017 unique clinic attendees. All of the participants had undergone blood testing at the clinic between August and October 2021, and their remaining serum was analyzed for antibodies to E. histolytica alongside the routine clinical data already collected during their visits. Because the analysis was retrospective and relied on specimens and records gathered for routine care, the ethics committee waived the requirement for individual informed consent, and the study was conducted in accordance with the Declaration of Helsinki.

Serology, the technique at the heart of the study, does not detect the parasite itself. Instead, it measures the immune system’s memory of exposure, revealing who has encountered the organism at some point in the past. That distinction matters for interpretation: a positive antibody result does not prove that a person is currently shedding the parasite in their stool, nor does it indicate when infection occurred or in which direction transmission moved between partners. What it does provide is a population-level snapshot of how commonly exposure has occurred, and in this clinic the snapshot was striking. Overall seropositivity stood at 10.7 percent, with a 95 percent confidence interval of 9.0 to 12.8 percent, a yield the authors note is comparable to the 7.5 percent positivity rate for Chlamydia trachomatis detected in the same clinic population over the same period.

The burden was not distributed evenly. Among men who have sex with men (MSM), 16.1 percent tested seropositive, a figure consistent with earlier international reports that have identified MSM as a group at elevated risk for enteric sexually transmitted infections. Female sex workers showed a seropositivity rate of 9.1 percent, while men who did not report sex with men came in at 8.9 percent. Women who were not sex workers had the lowest rate, at 3.9 percent. The pattern suggests that while risk concentrates in the groups historically emphasized in the literature, exposure is not confined to them, and that clinic-defined behavioral categories capture a gradient of risk rather than a simple divide between high- and low-risk populations.

One of the study’s most telling signals emerged when the researchers examined the relationship between seropositivity and the number of concurrent STIs a participant carried. Positivity rose steadily as the count of simultaneous infections increased, a trend that reached statistical significance with a p value for trend of 0.004. This dose-response-like pattern is epidemiologically meaningful because it links parasite exposure to the same behavioral and network factors that drive classical STIs, rather than to contaminated food or water, the traditional routes of amebiasis transmission. In other words, the more a person’s sexual network exposed them to other STIs, the more likely they were to have encountered E. histolytica as well.

To disentangle independent risk factors, the team built multivariable logistic regression models that adjusted for demographic and clinical characteristics simultaneously. Two factors stood out in the overall model. Attendees aged 40 years or older had roughly three times the odds of seropositivity compared with younger participants, with an adjusted odds ratio of 3.33 and a 95 percent confidence interval of 1.99 to 5.63. Positivity for Neisseria gonorrhoeae, the bacterium causing gonorrhea, was also independently associated with parasite exposure, carrying an adjusted odds ratio of 2.99 with a confidence interval of 1.11 to 7.19. The gonorrhea association is particularly intriguing because it suggests that a positive gonorrhea test could serve as a practical clinical marker flagging patients who may benefit from a conversation about enteric parasite risk.

The Japanese context gives the findings added urgency. E. histolytica has been increasingly recognized in Japan as a sexually transmissible enteric pathogen, particularly in urban sexual networks, yet the country’s ability to track temporal trends suffered a setback in 2018 when widely used serologic test kits were discontinued. Surveillance data interpretation has been difficult ever since, because changes in reported case numbers may reflect shifts in testing availability rather than true changes in transmission. By generating fresh seroprevalence estimates from a well-characterized clinic population, the new study offers a benchmark that can anchor future surveillance efforts and help public health officials distinguish genuine epidemiological change from artifacts of the diagnostic supply chain.

Clinically, the authors are careful about what their data can and cannot support. Because serology does not establish current shedding or the direction of transmission, they frame the results as evidence for risk-informed assessment, counseling, and confirmatory testing pathways in metropolitan STI services, rather than as proof of active spread across all sexual networks. In practice, that could mean that clinicians seeing patients with gonorrhea, multiple concurrent STIs, or other markers of elevated exposure consider adding questions about gastrointestinal symptoms and relevant exposures, and pursue confirmatory diagnostics such as stool antigen testing or molecular assays when amebiasis is suspected. Such pathways would be especially relevant for patients with symptoms like prolonged diarrhea, abdominal pain, or unexplained colitis, in whom untreated invasive amebiasis can cause serious morbidity.

The study also carries implications for how STI clinics think about the microbiological landscape of sexual health more broadly. Over the past decade, researchers have documented sexual transmission of several enteric pathogens, including Shigella species, lymphogranuloma venereum strains of Chlamydia trachomatis, and more recently mpox, prompting calls to widen the diagnostic lens beyond the classic STI panel. The new data from Tokyo reinforce the message that a clinic visit for an STI is also an opportunity to detect enteric infections that patients may not mention and that clinicians may not think to test for. Integrating serology or stool-based diagnostics into routine care for higher-risk subgroups, the authors suggest, could uncover a hidden burden that current screening algorithms miss entirely.

Limitations temper the conclusions. The analysis came from a single specialized clinic in Tokyo, so the results may not generalize to primary care settings, rural populations, or other countries. The cross-sectional design captures a single moment in time and cannot establish when exposure occurred or how it related to specific sexual practices. And because the serum testing relied on stored specimens collected for routine purposes, some clinical details available in dedicated research cohorts were necessarily absent. Still, the authors argue, the sheer scale of exposure observed, comparable to one of the most common bacterial STIs in the same population, makes a compelling case that E. histolytica deserves a place in risk-informed screening conversations, surveillance planning, and clinical guidelines for metropolitan sexual health services. As sexual networks and diagnostic technologies evolve, studies like this one provide the evidence base needed to decide which infections belong on the routine testing menu and which patients stand to benefit most from broader screening.

Subject of Research: Seroprevalence of the enteric parasite Entamoeba histolytica among sexually transmitted infection clinic attendees in Japan

Article Title: Entamoeba histolytica seropositivity among STI clinic attendees in Japan: implications for risk-informed screening and surveillance

Article References: Yanagawa, Y., Okuhama, A., Kawashima, A., Shiojiri, D., Gatanaga, H., & Watanabe, K. (2026). Entamoeba histolytica seropositivity among STI clinic attendees in Japan: implications for risk-informed screening and surveillance. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14392-2

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14392-2

Keywords: Entamoeba histolytica, amebiasis, sexually transmitted infection, seropositivity, STI clinic, men who have sex with men, gonorrhea, chlamydia, screening, surveillance, public health, Japan