Two promoters with distinct activities in different tissues drive the expression of heparanase in Xenopus

In Xenopus laevis embryos, heparanase, the enzyme that degrades heparan sulfate, is synthesized as a preproheparanase (XHpaL) and processed to become enzymatically active (XHpa active). A short nonenzymatic heparanase splice variant (XHpaS) is also expressed. Using immunohistochemistry, Western blot, and heparanase promoter analysis, we studied the dynamic developmental expression of the three heparanases. Our results indicate that (1) all three isoforms are maternally expressed; (2) XHpaS is a developmental variant; (3) in the early embryo, heparanase is localized to both the plasma membrane and the nucleus; (4) several tissues express heparanase, but expression in the developing nervous system is most evident; (5) two promoters with distinct activities in different tissues drive heparanase expression; (6) Oct binding transcription factors may modulate heparanase promoter activity in the early embryo. These data argue that heparanase is expressed widely during development, but localization and levels are finely regulated.