Mise en évidence de glycogène et d’une activité de la glycogène synthétase dans l’ébauche hépatique aux stades précoces du développement embryonnaire chez le poulet

Abstract

ABSTRACT Detection of glycogen and glycogen synthetase activity in the hepatic primordium of chick embryo at early developmental stages Glycogen has been detected cytochemically in the chick hepatic primordium at early developmental stages. The cytochemical methods used are PAS according to Hotchkiss & MacManus after fixation by Gendre’s fluid at —20 °C and rapid dehydration at 4 °C and Thiery’s technique for polysaccharide detection at the electron microscopic level. Previous authors reported that glycogen appears in the hepatocytes during the sixth or seventh day of incubation in the chick embryo. In fact, the more sensitive methods used here show that this substance is present in the determined presumptive hepatic endoderm as early as the 20-somite stage, some hours before the formation of the primary hepatic bud. Glycogen is present in an approximately constant amount in the differentiating hepatic endoderm as β particles (according to Drochmans’ nomenclature) from the 20-somite stage to the sixth day of incubation. Then the hepatocyte glycogen content increases rapidly as had previously been shown by biochemical methods and a rosettes appear in the cell. A glycogen synthetase activity has been detected at the end of the fourth day of incubation (96 h). This activity increases sharply from the sixth day of incubation to reach a maximal value at .12 days and then decreases until hatching. The possible regulatory mechanisms of glycogen synthesis in differentiating liver cells of avian embryos are discussed.