SLC35D3 is a solute carrier transporter with multiple distinct functions across different cell types and subcellular compartments. In neurons, SLC35D3 localizes to synaptic vesicles and functions as a vesicular transporter for UDP-glucose 1, suggesting a role in neurotransmission and neuromodulation. SLC35D3 also regulates dopamine signaling by controlling the plasma membrane localization of dopamine receptor D1 (D1R) through its localization to the endoplasmic reticulum and early endosomes 2. Mutations in SLC35D3 impair D1R trafficking and cause metabolic syndrome in mice, characterized by obesity and reduced dopaminergic signaling in striatal neurons; this phenotype is reversible with D1R agonist administration 2. In megakaryocytes and platelets, SLC35D3 is critical for dense granule biogenesis and hemostasis, though the precise molecular mechanism remains unclear 3, 4. Clinically, SLC35D3 mRNA expression in lymph nodes serves as a biomarker for detecting colorectal cancer metastases and predicting patient recurrence risk and prognosis 5, 6, 7. Collectively, SLC35D3 functions as both a nucleotide sugar transporter and a trafficking regulator essential for neural dopamine signaling and hematopoietic homeostasis.