Utheim, T. P. | Search bioRxiv

bioRxiv2025

The glutamine transporter Slc38a1 is widely expressed in the embryonic neurogenic niches and impacts neuronal volume, survival, and morphology

The amino acid glutamine, and its derivatives glutamate and GABA, are pivotal for neurogenesis. However, how glutamine is mechanistically supplied to the cells in the neurogenic niches and its broader impact on neurodevelopment, remain poorly characterized. The Solute carrier family 38 member 1 (Slc38a1) exhibits high affinity for glutamine and accumulates glutamine in select cells. We investigated whether Slc38a1 is essential for neurogenesis and whether it has an impact on brain structure and function. Slc38a1 mRNA transcript and protein are widely expressed in the embryonic brain, including in the dorsal pallium and sub-pallium. At embryonic day 15.5, Slc38a1 localizes in neuronal stem cells in the ventricular zone in the forebrain, while it localizes in mature neurons in the sub-ventricular zone of the hindbrain. In the adult brain, Slc38a1 is not detected in neuronal stem cells in the sub-granular zone, however, it is highly enriched in mature local parvalbumin+ and somatostatin+ interneurons and ependyma. Analyses of single-cell RNA sequencing data further reveal that both the number of Slc38a1-expressing cells and the average transcript level of Slc38a1 are significantly higher in embryo brain cells compared to adults. In the embryo, Slc38a1 transcripts are particularly enriched in immature neuronal lineages and embryonic oligodendrocyte precursor populations, whereas in the adult, expression is more prominent in neural progenitor cells and radial glia. Disruption of Slc38a1 in mice impacts body weight, brain size and glutamatergic neuronal volume, while dendritic arborization is diminished and cellular life span is shortened. Altogether, Slc38a1 is essential for normal neurodevelopment, indirectly regulates adult neurogenesis in the sub-granular zone and influence neuronal morphology and cell viability.

neuroscience↗

bioRxiv2025

Mapping galectin-3 ligands in tear fluid establishes spliceoform-dependent lacritin binding

Galectin-3 (Gal-3) is a carbohydrate-binding protein which plays crucial roles in inflammation, immune response, cell migration, autophagy, and signaling. At the ocular surface, Gal-3 is also known to crosslink transmembrane mucins across the epithelial cell glycocalyx, forming lattice structures important for barrier function. However, the biological role of Gal-3 in circulating tear fluid remains largely unexplored. Similarly, whether Gal-3 engages extracellular glycoproteins in tears to affect downstream biological processes has yet to be investigated. As increased Gal-3 levels in tears are known to correlate with ocular pathologies such as dry eye disease (DED), we sought to elucidate the Gal-3 interactome in tear fluid and uncover biological insights into the function of Gal-3 beyond adhesion to the epithelial cell surface. Here, we combined ELISA, lectin affinity enrichment, mass spectrometry (MS)-based glycoproteomics, and lectin blotting to uncover Gal-3 interactors and their associated glycoepitopes. Overall, we report nearly 100 proteins enriched from tear fluid across 3 different patients, identifying proteins involved in immune response, inflammation, and antimicrobial activity. Most notably, we report lacritin as a novel ligand for Gal-3 and demonstrate that specific glycoforms of lacritin bearing core 2 O-glycans preferentially engage with Gal-3. Lastly, we show that the Gal-3-lacritin axis is spliceoform-specific and dependent on lacritin multimerization. Taken together, this study elucidates new ligands for Gal-3 in tear film and reveals mRNA splicing and multimerization as new biochemical mechanisms that fine-tune Gal-3 binding events.

biochemistry↗