Podocalyxin, a sialoglycoprotein, is thought to be the major constituent of the glycocalyx of podocytes. It is a member of the CD34 family of transmembrane sialomucins. It coats the secondary foot processes of the podocytes. It is negatively charged and thus functions to keep adjacent foot processes separated, thereby keeping the urinary filtration barrier open. This function is further supported by knockout studies in mice which reveal an essential role in podocyte morphogenesis. Podocalyxin is also upregulated in a number of cancers and is frequently associated with poor prognosis. Sialylated, O-glycosylated glycoforms of podocalyxin expressed by colon carcinoma cells possess L-selectin and E-selectin binding activity, and may be pivotal to the metastatic spread of colon carcinoma cells.