Tag: Dictyostelium

Background: Aerobic eukaryotes utilize O₂ to oxidize metabolites and generate ATP. The response to oxygen deprivation leads to migration to locations with more favorable concentrations (aerotaxis), differentiation, metabolic reprogramming, or more global stress responses. In mammals, changes in gene expression are particularly well studied, with the involvement of the Hypoxia-Inducible Factor (HIF-1), which regulates the transcription of hundreds of genes. However, the protist kingdom lacks the HIF-dependent transcriptional response network to adapt to low O₂ levels, and their hypoxic adaptation remains unexplored.

Results: To address the scale and scope of hypoxic responses in protists, we characterized transcriptomic and proteomic changes when the social amoeba Dictyostelium is subjected to low (1%) O₂ under nutritive conditions over 24 h followed by reoxygenation. Remarkably, 32% of the transcripts quantified were differentially expressed during hypoxia, with greatest changes associated with early (1 h) and late phases (24 h). Protein changes were modestly correlated with and generally lagged behind transcriptional changes. Correlated changes were observed for transcripts and proteins associated with various metabolic, anabolic, and catabolic pathways, as well as chromosome organization, cell cycling, vesicular trafficking, and signaling. Interestingly, transcripts associated with the cAMP signaling pathway normally triggered by starvation were also up-regulated during chronic hypoxia. Additionally, we studied the molecular mechanisms driving the transcriptomic response. Analysis of 4 marker genes showed extremely rapid responses that were graded over a range of O₂ levels, with differential responses to inhibitors affecting protein synthesis and mitochondria, suggesting multiple induction mechanisms driving the transcriptomic response.

Conclusion: Overall, the amoebal response to a low but non-toxic O₂-level resulted in massive and temporal remodeling of the transcriptome and proteome. This complex expression changes extend beyond simple metabolic adaptation and point toward a multiprong adaptation strategy.

Julie Hesnard, Elisabet Gas-Pascual, Hanke van der Wel, Olivier Cochet-Escartin, Stephane Joly, Jean-Paul Rieu, Christopher M West, Christophe Anjard. BMC Genomics. 2025 Dec 29;26(1):1143. doi: 10.1186/s12864-025-12328-9.

Cellular adaptations to change often involve post-translational modifications of nuclear and cytoplasmic proteins. An example found in protists and plants is the modification of serine and threonine residues of dozens to hundreds of nucleocytoplasmic proteins with a single fucose (O-fucose). A nucleocytoplasmic O-fucosyltransferase occurs in the pathogen Toxoplasma gondii, the social amoeba Dictyostelium, and higher plants, where it is called Spy because mutants have a spindly appearance. O-fucosylation, which is required for optimal proliferation of Toxoplasma and Dictyostelium, is paralogous to the O-GlcNAcylation of nucleocytoplasmic proteins of plants and animals that are involved in stress and nutritional responses. O-fucose was first discovered in Toxoplasma using Aleuria aurantia lectin, but its broad specificity for terminal fucose residues on N- and O-linked glycans in the secretory pathway limits its use. Here we present affinity-purified rabbit antisera that are selective for the detection and enrichment of proteins bearing fucose-O-Ser or fucose-O-Thr. These antibodies detect numerous nucleocytoplasmic proteins in Toxoplasma, Dictyostelium, and Arabidopsis, as well as O-fucose occurring on secretory proteins of Dictyostelium and mammalian cells except when blocked by further glycosylation. The antibodies label Toxoplasma, Acanthamoeba, and Dictyostelium in a pattern reminiscent of O-GlcNAc in animal cells including nuclear pores. The O-fucome of Dictyostelium is partially conserved with that of Toxoplasma and is highly induced during starvation-induced development. These antisera demonstrate the unique antigenicity of O-fucose, document the conservation of the O-fucome among unrelated protists, and enable the study of the O-fucomes of other organisms possessing O-fucosyltransferase-like genes.IMPORTANCEO-fucose (O-Fuc), a form of mono-glycosylation on serine and threonine residues of nuclear and cytoplasmic proteins of some parasites, other unicellular eukaryotes, and plants, is understudied because it is difficult to detect owing to its neutral charge and lability during mass spectrometry. Yet, the O-fucosyltransferase enzyme (OFT) is required for optimal growth of the agent for toxoplasmosis, Toxoplasma gondii, and an unrelated protist, the social amoeba Dictyostelium discoideum. Furthermore, O-fucosylation is closely related to the analogous process of O-GlcNAcylation of thousands of proteins of animal cells, where it plays a central role in stress and nutritional responses. O-Fuc is currently best detected using Aleuria aurantia lectin (AAL), but in most organisms, AAL also recognizes a multitude of proteins in the secretory pathway that are modified with fucose in different ways. By establishing the potential to induce highly specific rabbit antisera that discriminate O-Fuc from all other forms of protein fucosylation, this study expands knowledge about the protist O-fucome and opens a gateway to explore the potential occurrence and roles of this intriguing posttranslational modification in bacteria and other protist pathogens such as Acanthamoeba castellanii.

Megna Tiwari, Elisabet Gas-Pascual, Manish Goyal, Marla Popov, Kenjiroo Matsumoto, Marianne Grafe, Ralph Gräf, Robert S Haltiwanger, Neil Olszewski, Ron Orlando, John C Samuelson, Christopher M West. mSphere. 2025 Feb 6:e0094524. doi: 10.1128/msphere.00945-24.