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 mi tochondrial form, PEPCK-M, which have novel patterns of expression. He re we show that, in contrast to mammals, in which PEPCK-C is not prese nt in liver until after birth, avian PEPCK-C is expressed throughout e mbryonic life with mRNA levels gradually decreasing as development pro ceeds and becoming negligible at time of hatching. In addition two dis tinct mRNAs for PEPCK-M are expressed during development with specific patterns that vary among individual birds. These differences are like ly to be genetic, as hormonal treatment of a chicken hepatoma cell lin e indicates that whereas the mRNA levels for PEPCK-C are hormonally re gulated, the expression of PEPCK-M mRNA is unresponsive.