Expression of the genes for the mitochondrial and cytosolic forms of phosphoenolpyruvate carboxykinase in avian liver during development.

Gluconeogenesis in the chicken has unique features due in part to the presence of two isozymes of PEPCK, a cytosolic form, PEPCK-C, and a mitochondrial form, PEPCK-M, which have novel patterns of expression. Here we show that, in contrast to mammals, in which PEPCK-C is not present in liver until after birth, avian PEPCK-C is expressed throughout embryonic life with mRNA levels gradually decreasing as development proceeds and becoming negligible at time of hatching. In addition two distinct mRNAs for PEPCK-M are expressed during development with specific patterns that vary among individual birds. These differences are likely to be genetic, as hormonal treatment of a chicken hepatoma cell line indicates that whereas the mRNA levels for PEPCK-C are hormonally regulated, the expression of PEPCK-M mRNA is unresponsive.