Changes in gene expression involved in energy utilization during chicken follicle development

Ovarian follicle development in egg-laying species is characterized by rapid growth in 7 days prior to ovulation when DNA and protein synthesis is markedly increased in the granulosa and theca cells. However, energy and substrate sources to facilitate the extensive DNA and protein synthesis necessary for folliculogenesis have not been identified in avian species. The current study was undertaken to investigate the expression profiles of regulatory genes involved in glucose transport, glycolysis and fatty acid oxidation in the follicle membranes from the small white follicle (SWF) to follicle 1 (F1) stages of follicle development. In our analysis of glucose transporter (GLUT) isoform expression, the level of GLUT1 mRNA increased with follicle development while GLUT2, GLUT3 and GLUT8 mRNA levels were unaffected by follicle development. In contrast, the expression patterns of proteins involved in metabolism down-stream of glucose transport, including hexokinase (HK), pyruvate dehydrogenase E1α (PDH E1α) and citrate synthase (CS), did not vary with the developmental stage of the follicle, even during rapid follicle growth. Expression of genes related to β-oxidation of fatty acids (carnitine palmityl CoA transferase I and II, l-3-hydroxyacyl CoA dehydrogenase and long-chain acyl-CoA dehydrogenase), for which expression in the ovarian follicles of mammalian species has not previously been studied, was not changed consistently with the follicle development. These results suggest that both glucose and fatty acids might work as energy sources to ensure rapid follicle development in the chicken ovary, even though glycolysis and β-oxidation are not modulated by follicle development.