The human embryonic-fetal kidney endoplasmic reticulum phosphate-pyrophosphate transport protein.

Glucose-6-phosphatase is a multicomponent endoplasmic reticulum system comprising at least six different proteins, including a lumenal enzyme and several transport proteins. One of the transport proteins, T2beta, transports the substrate pyrophosphate and the product phosphate and its genetic deficiency is termed type 1c glycogen storage disease. We have used anti-T2beta antibodies for immunohistochemistry with image analysis and kinetic analysis of the glucose-6-phosphatase system to study for the temporal and spatial development of T2beta in human embryonic and fetal kidney. In metanephric kidney, there is an early predominance of T2beta expression in the ureteric bud derivatives and this changes with ontogeny such that developing nephrons, particularly proximal tubules, become dominant by mid-gestation. T2beta has the same spatial and temporal pattern as the glucose-6-phosphatase enzyme in both mesonephric and metanephric kidney. Pyrophosphate transport capacity is appropriate for the amount of glucose-6-phosphatase activity present in mid-gestation fetal kidney, in contrast to liver, where pyrophosphate transport capacity is developmentally delayed. Increasing knowledge of the temporal and spatial expression of the glucose-6-phosphatase proteins and their catalytic roles in early human development is essential for the elucidation of the aetiology of renal disease in both type I glycogen storage diseases and the developmental disorders of the glucose-6-phosphatase system.