Expression of sulfated gp300 and changes in glycosylation during pancreatic development

The pancreatic zymogen granule membrane protein gp300 is the major sulfated glycoprotein of the mouse acinar cell and has been proposed to be an important structural component of the zymogen granule membrane. A prediction of this proposed function is that gp300 expression should be coordinately regulated with the digestive enzymes and appearance of zymogen granules during differentiation of acinar cells in fetal development. By Western blots and immunolocalization with a polyclonal antiserum to gp300, we found that gp300 protein expression paralleled expression of amylase and the appearance of zymogen granules in differentiating acinar cells. Lectin blots were performed to assess the glycoconjugate composition of gp300 during development. Using the fucose binding lectin Ulex europaeus I, we found that gp300 acquires this carbohydrate only postnatally, temporally correlated with weaning. In addition, gp300 showed complex changes during postnatal development in reactivity with the galactose binding lectin peanut agglutinin (PNA) and the sialic acid binding lectin Maackia amuresis (MAA). Levels of reactivity of PNA and MAA were reciprocal, suggesting that sialylation of galactose (which can block peanut agglutinin binding) was not constant on gp300 during development.