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<p>Glucose serves as a primary energy source for ATP production across diverse taxa; however, its hydrophilic nature necessitates protein-mediated transport across lipid bilayers. In multicellular organisms, glucose uptake triggers insulin secretion, which subsequently promotes the translocation of glucose transporters to the plasma membrane, thereby enhancing glucose uptake. Although the existence of insulin in unicellular eukaryotes remains controversial, this study investigates insulin-like genes in the ciliate <i>Tetrahymena thermophila</i>. We identified a first putative insulin-like peptide-coding gene, designated as INS1, along with six additional putative INS-like genes. The INS1 preproprotein contains a putative N-terminal secretory signal peptide and six conserved cysteine residues. Proteolytic cleavage of the predicted signal sequence from the ~7.26&#xa0;kDa prepro-INS1 yields a ~ 4.6&#xa0;kDa pro-INS1 protein. Furthermore, in silico structural modelling indicates that INS1 adopts a characteristic insulin-specific fold. Our results demonstrated that glucose depletion upregulates INS1 mRNA expression in starved and conjugating cells, but not in vegetative cells. Functional assays showed that affinity-purified INS1-10xHis and recombinant INS1-sfGFP overexpression significantly increases glucose uptake, enhancing cellular proliferation and survival. Under low-glucose conditions, INS1-sfGFP was localized to vesicles at the cell cortex near the plasma membrane. Collectively, this study provides evidence for insulin-like peptide coding genes in ciliates. We propose a glucose-responsive secretion mechanism for insulin-like peptides in <i>T. thermophila</i>, suggesting that the evolutionary origin of insulin-like peptides may predate the emergence of multicellularity.</p>

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Identification and functional analysis of insulin-like gene(s) in the unicellular eukaryote, Tetrahymena thermophila

  • 期刊论文

  • 发表日期：

    2026年6月20日

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  • Ayça Fulya Üstüntanir Dede,
  • Muhittin Arslanyolu

摘要

Glucose serves as a primary energy source for ATP production across diverse taxa; however, its hydrophilic nature necessitates protein-mediated transport across lipid bilayers. In multicellular organisms, glucose uptake triggers insulin secretion, which subsequently promotes the translocation of glucose transporters to the plasma membrane, thereby enhancing glucose uptake. Although the existence of insulin in unicellular eukaryotes remains controversial, this study investigates insulin-like genes in the ciliate Tetrahymena thermophila. We identified a first putative insulin-like peptide-coding gene, designated as INS1, along with six additional putative INS-like genes. The INS1 preproprotein contains a putative N-terminal secretory signal peptide and six conserved cysteine residues. Proteolytic cleavage of the predicted signal sequence from the ~7.26 kDa prepro-INS1 yields a ~ 4.6 kDa pro-INS1 protein. Furthermore, in silico structural modelling indicates that INS1 adopts a characteristic insulin-specific fold. Our results demonstrated that glucose depletion upregulates INS1 mRNA expression in starved and conjugating cells, but not in vegetative cells. Functional assays showed that affinity-purified INS1-10xHis and recombinant INS1-sfGFP overexpression significantly increases glucose uptake, enhancing cellular proliferation and survival. Under low-glucose conditions, INS1-sfGFP was localized to vesicles at the cell cortex near the plasma membrane. Collectively, this study provides evidence for insulin-like peptide coding genes in ciliates. We propose a glucose-responsive secretion mechanism for insulin-like peptides in T. thermophila, suggesting that the evolutionary origin of insulin-like peptides may predate the emergence of multicellularity.