Podoplanin, also known as glycoprotein 38 (gp38), PA2.26 antigen, T1alpha (T1A), and aggrus, is a 38 kDa type I transmembrane sialoglycoprotein and member of the podoplanin family. Podoplanin is synthesized as a 172 amino acid (aa) precursor with a 22 aa signal sequence, a 119 aa extracellular domain (ECD), a 21 aa transmembrane region, and a short, 10 aa cytoplasmic tail. The ECD contains abundant Ser/Thr residues as potential sites for Oglycosylation, and the cytoplasmic region contains putative sites for kinase C and cAMP phosphorylation. Mouse Podoplanin shares 77% and 46% aa sequence identity with rat and human Podoplanin, respectively. Podoplanin is expressed on glomerular epithelial cells (podocytes), type I lung alveolar cells, lymphatic endothelial cells, and on numerous tumors including colorectal tumors, squamous cell carcinomas, testicular seminoma, and brain tumors. One study shows high expression of Podoplanin mRNA in placenta, lung, skeletal muscle, and heart, and weaker levels in brain, kidney, and liver. Podoplanin is the ligand for Ctype lectin like receptor 2 (CLEC2). Their association is dependent on sialic acid on Oglycans of Podoplanin. Through its association with CLEC2, Podoplanin induces platelet aggregation and tumor metastasis. Podoplanin is also necessary for lymphatic vessel formation, normal lung cell proliferation and alveolus formation at birth.